Data Set ID: 
SPL1BTB

SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures, Version 4

This Level-1B (L1B) product provides calibrated estimates of time-ordered geolocated brightness temperatures measured by the Soil Moisture Active Passive (SMAP) passive microwave radiometer. SMAP L-band brightness temperatures are referenced to the Earth's surface with undesired and erroneous radiometric sources removed.

This is the most recent version of these data.

Version Summary: 

Changes to this version include:

  • Added procedure to correct brightness temperatures for water/land contamination near coastlines. New data fields for this correction include:
    footprint_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_surface_corrected, and tb_v_surface_corrected.
  • Improved Level-1 calibration coefficients and reflected galaxy correction. To refine reflected galaxy correction over ocean, NOAA NCEP ocean roughness data have been added (wind_direction_ancillary, wind_speed_ancillary).

COMPREHENSIVE Level of Service

Data: Data integrity and usability verified; data customization services available for select data

Documentation: Key metadata and comprehensive user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services

See All Level of Service Details

Parameter(s):
  • Microwave > Antenna Temperature
  • Microwave > Brightness Temperature
Data Format(s):
  • HDF5
Spatial Coverage:
N: 86.4, 
S: -86.4, 
E: 180, 
W: -180
Platform(s):SMAP Observatory
Spatial Resolution:
  • 47 km x 36 km
Sensor(s):SMAP L-BAND RADIOMETER
Temporal Coverage:
  • 31 March 2015
Version(s):V4
Temporal Resolution49 minuteMetadata XML:View Metadata Record
Data Contributor(s):Piepmeier, J. R., P. Mohammed, J. Peng, E. J. Kim, G. De Amici, M. J. Chaubell, and C. Ruf.

Geographic Coverage

Other Access Options

Other Access Options

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As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Piepmeier, J. R., P. Mohammed, J. Peng, E. J. Kim, G. De Amici, M. J. Chaubell, and C. Ruf. 2018. SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/VA6W2M0JTK2N. [Date Accessed].
Created: 
21 December 2018
Last modified: 
3 December 2019

Data Description

Parameters

The SMAP L-Band Radiometer measures antenna temperatures referenced to the instrument feedhorn before and after RFI mitigation. SMAP antenna temperatures are then used to calculate the four Stokes parameters: TV, TH, T3, and T4 at 1.41 GHz. These parameters represent the vertically and horizontally polarized brightness temperatures (TBs), and the third and fourth cross-polarized brightness temperatures, respectively. The cross-polarized T3-channel measurement can be used to correct for possible Faraday rotation caused by charged particles in the upper atmosphere.

Refer to the Appendix of this document for details on all parameters.

File Information

Format

Data are in HDF5 format. For software and more information, including an HDF5 tutorial, visit the HDF Group's HDF5 website.

File Contents

As shown in Figure 1, each HDF5 file is organized into the following main groups, which contain additional groups and/or data sets:

Figure 1. Subset of File Contents
For a complete list of file contents for the SMAP Level-1B brightness temperature product, refer to the Appendix. 

Data Fields

Each file contains the main data groups summarized in this section. For a complete list and description of all data fields within these groups, refer to the Appendix of this document. Note that data array dimensions and sizes vary for this product.

Brightness Temperature
Includes brightness temperatures at each footprint referenced to the surface of the Earth with error sources and undesirable radiometric sources removed, such as atmospheric effects and solar, lunar, and galactic emissions. A second set of further corrected brightness temperatures are also provided, such as tb_h_surface_corrected (as opposed to tb_h). For these brightness temperatures, an additional correction procedure has been applied to correct anomalous water and land values; see the "Water/Land Contamination Correction" section for details. 

This group also includes antenna temperatures (TAs) referenced to the feedhorn before and after RFI mitigation, error source values, brightness temperature error, and Noise Equivalent Delta Temperature (NEDT). Many parameters are specifically designated for horizontal and vertical polarizations as well as the 3rd and 4th Stokes parameters.

Calibration Data

Includes fullband and subband calibration coefficients. Among these coefficients are instrument component losses, noise temperatures, physical temperatures, calibration gain and offset factors and phase values. The contents were corrected for detected RFI.

High Resolution Calibration Data

Includes subband calibration coefficients. Among these coefficients are instrument component losses, noise temperatures, physical temperatures, calibration gain and offset factors and phase values. The contents were corrected for detected RFI.

Spacecraft Data
Includes elements that specify either geometric or geographic information that are representative of each entire antenna scan of the instrument swath. Major elements include the spacecraft time, position, velocity, and attitude. Values in the spacecraft data group are representative of all brightness temperatures acquired during the corresponding antenna scan.

Metadata Fields

Includes all metadata that describe the full content of each file. For a description of all metadata fields for this product, refer to the Product Specification Document.

File Naming Convention

Files are named according to the following convention, which is described in Table 1:

SMAP_L1B_TB_[Orbit#]_[A/D]_yyyymmddThhmmss_RLVvvv_NNN.[ext]

For example:

SMAP_L1B_TB_03891_D_20151024T155359_R13242_001.h5

Where:

Table 1. File Naming Conventions
Variable Description
SMAP Indicates SMAP mission data

L1B_TB

Indicates specific product (L1B: Level-1B; TB: Brightness Temperature)

[Orbit#] 5-digit sequential number of the orbit flown by the SMAP spacecraft when data were acquired. Orbit 00000 began at launch. Orbit numbers increment each time the spacecraft flies over the southernmost point in the orbit path.
[A/D]

Half-orbit pass of the satellite, such as: 
A: Ascending (where satellite moves from South to North, and 6:00 p.m. is the local solar time)
D: Descending (where satellite moves from North to South, and 6:00 a.m. is the local solar time)

yyyymmddThhmmss Date/time in Universal Coordinated Time (UTC) of the first data element that appears in the product, where:
yyyymmdd 4-digit year, 2-digit month, 2-digit day
T Time (delineates the date from the time, i.e. yyyymmddThhmmss)
hhmmss 2-digit hour, 2-digit month, 2-digit second
RLVvvv Composite Release ID, where:
R Release
L Launch Indicator (1: post-launch standard data)
V 1-Digit Major Version Number
vvv 3-Digit Minor Version Number
Example: R13242 indicates a post-launch data product with a version of 3.242.
NNN Number of times the file was generated under the same version for a particular date/time interval (002: 2nd time)
.[ext] File extensions include:
.h5 HDF5 data file
.qa Quality Assurance file
.xml XML Metadata file

File Size

Each half-orbit file is approximately 46 MB.

File Volume

The daily data volume is approximately 1.4 GB.

Coverage spans from 180°W to 180°E, and from approximately 86.4°N to 86.4°S. The gap in coverage at both the North and South Pole, called a pole hole, has a radius of approximately 400 km. The swath width is 1000 km, enabling nearly global coverage every two to three days.

Spatial Information

Coverage

Coverage spans from 180°W to 180°E, and from approximately 86.4°N to 86.4°S. The gap in coverage at both the North and South Pole, called a pole hole, has a radius of approximately 400 km. The swath width is 1000 km, enabling nearly global coverage every two to three days.

Spatial Coverage Map

Figure 2 shows the spatial coverage of the SMAP L-Band Radiometer for one descending half orbit, which comprises one file of this data set.

Figure 2. Spatial coverage map displaying one descending half orbit of the SMAP L-Band Radiometer. 

Resolution

The instantaneous field of view of the radiometer footprint is approximately 36 x 47 km; the effective field of view of brightness temperatures in the Level-1B brightness temperature product is 39 x 47 km. The native spatial resolution of the radiometer footprint is approximately 36 km.

Temporal Information

Coverage

Coverage spans from 31 March 2015 to present.

Satellite and Processing Events

Due to instrument maneuvers, data downlink anomalies, data quality screening, and other factors, small gaps in the SMAP time series will occur. Details of these events are maintained on two master lists:

SMAP On-Orbit Events List for Instrument Data Users
Master List of Bad and Missing Data

A significant gap in coverage occurred between 19 June and 23 July 2019 after the SMAP satellite went into Safe Mode. A brief description of the event and its impact on data quality is available in the SMAP Post-Recovery Notice.

Latencies

FAQ: What are the latencies for SMAP radiometer data sets?

Resolution

Each Level-1B half-orbit file spans approximately 49 minutes.

Data Acquisition and Processing

Background

The objective of the Level-1B brightness temperature algorithm is to convert digital counts in the instrument telemetry into time-ordered, geolocated brightness temperatures within the main beam referenced to the Earth's surface. The algorithm theory is similar to what has been developed and implemented for decades for other satellite radiometers. SMAP includes two key features heretofore absent from satellite-borne radiometers: RFI detection and mitigation, and measurement of the third and fourth Stokes parameters using digital correlation.

This section contains a description of the sources contributing to the total apparent temperature seen at the input to the SMAP main reflector. The brightness temperature of a source (measured in kelvins) can be described in terms of the product of the physical temperature and the emissivity of the source. Emissivity is, in general, polarization dependent, thus differentiating brightness temperature into TBV and TBH for the vertical and horizontal polarizations, respectively. These are the first two modified Stokes parameters. The real part of the complex correlation between these two components is measured by the third modified Stokes parameter, represented in brightness temperatures as T3. The fourth Stokes parameter, T4, measures the imaginary part of the correlation. For this document, a vector of modified Stokes parameters is shown by:

(Equation 1)

where θ and Φ are the elevation and azimuth of a spherical coordinate system centered on the radiometer antenna boresight vector. Important sources of radiation at L-band are the Earth's land and sea, the cosmic background radiation, the sun, radiation sources outside our solar system, and the moon.

For an in-depth description of the theory of these measurements, refer to Section 4: Forward Model (TA to TB) of Piepmeier et al. (2016).

Acquisition

SMAP Level-1B radiometer brightness temperatures are processed from SMAP L1A Radiometer Time-Ordered Parsed Telemetry (SPL1AP). The Level-1A radiometer product contains parsed radiometer instrument telemetry.

Derivation Techniques and Algorithms

The raw radiometer instrument counts are converted to antenna temperatures and then to brightness temperatures to produce SMAP Level-1A and Level-1B products. The input data to the Level-1B brightness temperature algorithm are the SMAP L1A Radiometer Time-Ordered Parsed Telemetry data. The Level-1A Science Processing Software produces the Level-1A product in accordance with the Earth Observing System (EOS) Data Product Levels definition, which states that Level-1A data products are reconstructed, unprocessed instrument data at full resolution, are time-referenced and annotated with ancillary information.

The Level-1B radiometer brightness temperature Science Processing Software geolocates and radiometrically calibrates the Level-1A data to obtain antenna temperatures. Subsequent processing applies algorithms that detect and flag pixels for RFI. The data are then time and frequency averaged near the antenna's angular Nyquist rate. The Level-1B algorithm also compensates for sources of error or sources of radiometric energy not associated with emissivity of the Earth's surface. Those sources include Faraday rotation, energy detected by antenna sidelobes and spillover, atmospheric effects, solar radiation, lunar radiation, cosmic microwave background, galactic emission, and water/land contamination. 

Water/Land Contamination Correction 

To mitigate water and land contamination, the latest Level-1B algorithm includes a surface correction procedure for the brightness temperature contribution due to water (when the antenna boresight falls on a land location) or land (when the antenna boresight falls on a water location). Both the horizontally and vertically polarized L1B brightness temperatures are corrected for the presence of water or the presence of land within the antenna field of view (FOV). Over land, the resulting brightness temperatures will become warmer upon the removal of the contribution of water to the original uncorrected observations. Over water, the resulting brightness temperatures will become cooler upon the removal of the contribution of land to the original uncorrected observations. 

For example, the total measured temperature can be separated into two contributions: 

Eq. 2    (Equation 2)

If the footprint is on land, the following formula is applied:

      Eq. 3       (Equation 3)

If the footprint is on water, the following formula is applied:
   
  Eq. 4     (Equation 4)

where f is the water fraction, f=1 for pure water, and f=0 for pure land.

   
  Eq. 5   (Equation 5)

These water/land contamination corrections are performed when the following criteria are met:

  • If footprint boresight is over land as indicated by a static high-resolution land/water mask, then water contamination correction is performed
  • If footprint boresight is over water as indicated by a static high-resolution land/water mask, then land contamination correction is performed
  • Over land, water contamination correction is performed if antenna-gain-weighted water fraction </=0.9
  • Over water, land contamination correction is performed if antenna-gain-weighted water fraction > 0.1
  • Correction is performed only if sea ice fraction=0
  • Valid range for TB V polarization [50K: 340K]; values outside this range are replaced with fill values
  • Valid range for TB H polarization [30K: 340K]; values outside this range are replaced with fill values
  • Over land, if tb_surface_corrected < TB, then value is replaced with fill value
  • Over water, if tb_surface_corrected > TB, then value is replaced with fill value

For more details regarding the algorithm used to generate this product, refer to the latest ATBD, Piepmeier et al. (2018). 

Processing

This product is generated by the SMAP Science Data Processing System (SDS) at the Jet Propulsion Laboratory (JPL) in Pasadena, California USA. To generate this product, the processing software ingests both descending and ascending half-orbit files of the Level-1A brightness temperature data. The descending half orbits contain data acquired at very nearly 6:00 a.m. local solar time. The ascending half orbits contain data acquired at very nearly 6:00 p.m. local solar time.

The total number of radiometer science packets per antenna scan varies depending on the antenna rotation rate and integration time of the instrument. The resulting number of antenna footprints per scan is therefore variable. To preserve the shape of stored data elements, the size of certain dimensions is assigned a maximum value. Thus, fill values appear in the SMAP Level-1B brightness temperature product when a particular scan does not contain the maximum possible number of footprints.

Antenna temperatures are processed by RFI detection and mitigation algorithms (see Error Sources) where the pixels for a footprint that are flagged for RFI are removed and the remaining clean pixels are averaged to form an RFI-free antenna footprint. If all pixels for a particular footprint are flagged for RFI then the footprint antenna temperature is assigned the null value. The corresponding footprint brightness temperature (TB) value will also be assigned the null value since the RFI-free antenna footprint antenna temperatures are used to produce the time-ordered brightness temperature product. Subsequently, after pixels with RFI are flagged and dropped, the remaining clean pixels are used to compute the NEDT for that footprint. If all pixels are removed, the null value is assigned to the NEDT for that footprint. For more details, refer to Section C. RFI Detection and Mitigation (p. 33) of the SMAP Handbook.

Lastly, additional corrections are applied to brightness temperatures to correct for anomalous data values as a result of water/land contamination. 

Quality, Errors, and Limitations

Error Sources

L-Band anthropogenic Radio Frequency Interference (RFI), principally from ground-based surveillance radars, can contaminate radiometer measurements. Early measurements and results from the European Space Agency Soil Moisture and Ocean Salinity (SMOS) mission indicate that, in some regions, RFI is present and detectable. The SMAP radiometer electronics and algorithms have been designed to include features to mitigate the effects of RFI. The SMAP radiometer implements a combination of time and frequency diversity, kurtosis detection, and the use of 3rd and 4th Stokes parameter thresholds to detect and where possible mitigate RFI (Piepmeier et al. 2016, Bringer et al. 2017, Piepmeier et al. 2014). Data elements associated with subbands are included in the Level-1B radiometer product to track and enable RFI detection and mitigation. Further corrections are applied to mitigate water/land contamination. 

The input Level-1A radiometer data can also contain bit errors caused by noise in communication links and memory storage devices. The packets produced by the Consultative Committee on Space Data Systems (CCSDS) include error-detecting Cyclic Redundancy Checks (CRCs), which the Level-1A processor uses to flag errors.

Quality Assessment

For in-depth details regarding the quality of these data, refer to the Validated Assessment Report.

Quality Overview

SMAP data sets provide multiple means to assess quality. Each data set contains bit flags, uncertainty measures, and file-level metadata that provide quality information. The Appendix of this document and the Product Specification Document describe the specific bit flags, uncertainty measures, and file-level metadata contained in this data set.

Each SMAP HDF5 data file contains metadata with Quality Assessment (QA) metadata flags. These QA metadata flags are calculated and set by the SDS at JPL prior to delivery to the National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC). A separate, ISO 19115-compliant metadata file with an .xml file extension is also delivered to NSIDC DAAC with the HDF5 data file; it contains the same information as the file-level metadata.

A separate QA file with a .qa file extension is also associated with each data file. QA files are ASCII text files that contain statistical information in order to help users better assess the quality of the associated data file.

In addition, various levels of QA are conducted with Level-1B data. If a file passes QA, the SDS applies that file for higher-level processing, browse generation, active science QA, and data archive and distribution. If a product fails QA, it is never delivered to NSIDC DAAC.

Instrumentation

Description

For a detailed description of the SMAP instrument, visit the SMAP Instrument page at Jet Propulsion Laboratory (JPL) SMAP website.

Software and Tools

For tools that work with SMAP data, refer to the Tools web page.

Version History

Table 2. Version History
Version Date Version Changes
V1 July 2015 First public data release
V2 October 2015 No science change. CRID incremented to coincide with DOI correction for SPL2SMP and SPL3SMP. 
V3
 
April 2016 Changes to this version include:
  • Updated reflector thermal model
  • Reflector emissivity value back to baseline
  • All calibration coefficients updated back to 3/31/15
  • Direct Galaxy quality flag changed: set when s/c nadir > 5 degrees
  • Reflected Sun quality flag changed: set when specular solar theta <15 degrees
  • Sea ice fraction computation implemented
V4 June 2018

Changes to this version include:

  • Added procedure to correct brightness temperatures for water/land contamination near coastlines. New data fields for this correction include: footprint_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_surface_corrected, and tb_v_surface_corrected.
  • Improved Level-1 calibration coefficients and reflected galaxy correction. To refine reflected galaxy correction over ocean, NOAA NCEP ocean roughness data have been added (wind_direction_ancillary, wind_speed_ancillary).

Related Data Sets

SMAP Data at NSIDC | Overview

SMAP Radar Data at the ASF DAAC

Related Websites

SMAP at NASA JPL

Contacts and Acknowledgments

Investigators

Jeffrey R. Piepmeier, Priscilla N. Mohammed, 
Jinzheng Peng, Edward Kim, and Giovanni De Amici

NASA Goddard Space Flight Center
Greenbelt, MD

Chris Ruf
Space Physics Research Laboratory
University of Michigan
Ann Arbor, MI

References

References

Bringer, A., J. T. Johnson, P. N. Mohammed, J. R. Piepmeier, 2017. Performance of SMAP radiometer RFI detection algorithms and analysis of residual RFI sources. In Geoscience and Remote Sensing Symposium (IGARSS)2017 IEEE International, 1243-1246.

Piepmeier, J., G. De Amici, P. Mohammed, and J. Peng. 2017. Improved Calibration through SMAP RFI Change Detection. 

Piepmeier, J. R. et al. 2018. SMAP Algorithm Theoretical Basis Document: L1B Radiometer Product: Includes L1A and L1B, Rev. C. SMAP Project, NASA GSFC SMAP-006, NASA Goddard Space Flight Center, Greenbelt, MD. (PDF, 1.95 MB; see Technical References). 

Piepmeier, J. R. et al. 2016. SMAP Algorithm Theoretical Basis Document: L1B Radiometer Product: Includes L1A and L1B. SMAP Project, NASA GSFC SMAP-006, NASA Goddard Space Flight Center, Greenbelt, MD. (PDF, 1.94 MB; see Technical References). 

Piepmeier, J. R. , J. T. Johnson, P. N. Mohammed, D. Bradley, C. Ruf, M. Aksoy, R. Garcia, D. Hudson, L. Miles, and M. Wong. 2014. Radio-Frequency Interference Mitigation for the Soil Moisture Active Passive Microwave Radiometer. IEEE Transactions on Geoscience and Remote Sensing. 52(1):761-775. doi: https://dx.doi.org/10.1109/TGRS.2013.2281266.

Piepmeier, J. R., D. G. Long, and E. G. Njoku. 2008. Stokes Antenna Temperatures. IEEE Trans. Geosci. Remote Sens. 46(2):516-527.

Appendix - Data Fields

This appendix provides a description of all data fields within the SMAP L1B Radiometer Half-Orbit Time-Ordered Brightness Temperatures product.

  • Brightness_Temperature
  • Calibration_Data
  • High_Resolution_Calibration_Data
  • Metadata
  • Spacecraft_Data

For a description of metadata fields for this product, refer to the Product Specification Document.

Brightness_Temperature

Table A1 lists the elements in the Brightness_Temperature group. This group provides the time-ordered footprint averaged brightness temperatures (TBs) referenced to the Earth's surface with error sources removed. The group also includes geolocation information, antenna temperatures referenced to the feedhorn, before and after Radio Frequency Interference (RFI) mitigation, error sources, quality flags, brightness temperature error, and Noise Equivalent Delta Temperature (NEDT).

Within the Brightness_Temperature group, a distinct HDF5 data set stores each data element. The name of each data set object matches the data element that it stores. Table 1 lists the elements in the Brightness Temperature group. All the data elements in the Brightness Temperature group have the AntennaScan_Tb_Array shape. TheAntennaScan_Tb_Array shape describes a two-dimensional array. The slowest moving dimension represents a particular antenna scan and the second dimension represents the footprint.

Table A1. Brightness Temperature Data Fields
Data Field Name Type Shape Valid_Min Valid_Max Units Fill/Gap Value
antenna_earth_azimuth Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
antenna_look_angle Float32 AntennaScan_Tb_Array 0.0 180.0 Degrees -9999.0
antenna_scan_angle Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
antenna_sideloble_correction_3 Float32 AntennaScan_Tb_Array -0.5 6.0 Kelvin -9999.0
antenna_sideloble_correction_4 Float32 AntennaScan_Tb_Array -0.5 6.0 Kelvin -9999.0
antenna_sideloble_correction_h Float32 AntennaScan_Tb_Array -0.5 6.0 Kelvin -9999.0
antenna_sideloble_correction_v Float32 AntennaScan_Tb_Array -0.5 6.0 Kelvin -9999.0
atm_correction_h Float32 AntennaScan_Tb_Array 0.0 4.0 Kelvin -9999.0
atm_correction_v Float32 AntennaScan_Tb_Array 1 4 Kelvin -9999.0
atm_loss Float32 AntennaScan_Tb_Array 1.0 1.02 Kelvin -9999.0
earth_boresight_azimuth Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
earth_boresight_incidence Float32 AntennaScan_Tb_Array 0.0 90.0 Degrees -9999.0
faraday_rotation_angle Float32 AntennaScan_Tb_Array -90.0 90.0 Degrees -9999.0
faraday_rotation_correction_h Float32 AnntenaScan_Tb_Array -3.9 5.6 Kelvin -9999.0
faraday_rotation_correction_v Float32 AntennaScan_Tb_Array -3.9 5.6 Kelvin -9999.0
footprint_surface_status Uint16 AntennaScan_Tb_Array 0 1 N/A 65534
galactic_direct_correction_h Float32 AntennaScan_Tb_Array 0.3 0.6 Kelvin -9999.0
galactic_direct_correction_v Float32 AntennaScan_Tb_Array 0.3 0.6 Kelvin -9999.0
galactic_reflected_correction_3 Float32 AntennaScan_Tb_Array -0.4 4 Kelvin -9999.0
galactic_reflected_correction_4 Float32 AntennaScan_Tb_Array -0.4 4 Kelvin -9999.0
galactic_reflected_correction_h Float32 AntennaScan_Tb_Array -0.4 4.0 Kelvin -9999.0
galactic_reflected_correction_v Float32 AntennaScan_Tb_Array -0.4 4.0 Kelvin -9999.0
lunar_direct_phi Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
lunar_direct_theta Float32 AntennaScan_Tb_Array 0.0 180.0 Degrees -9999.0
lunar_specular_correction_3 Float32 AntennaScan_Tb_Array -0.2 2.0 Kelvin -9999.0
lunar_specular_correction_4 Float32 AntennaScan_Tb_Array -0.2 2.0 Kelvin -9999.0
lunar_specular_correction_h Float32 AntennaScan_Tb_Array -0.2 2.0 Kelvin -9999.0
lunar_specular_correction_v Float32 AntennaScan_Tb_Array -0.2 2.0 Kelvin -9999.0
lunar_specular_lat Float32 AntennaScan_Tb_Array -90 90 Degrees -9999.0
lunar_specular_lon Float32 AntennaScan_Tb_Array -180.0 179.999 Degrees -9999.0
lunar_specular_phi Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
lunar_specular_reflection_coefficient_h Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
lunar_specular_reflection_coefficient_v Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
lunar_specular_theta Float32 AntennaScan_Tb_Array 0.0 180.0 Degrees -9999.0
nedt_3 Float32 AntennaScan_Tb_Array 0.5 3.0 Kelvin -9999.0
nedt_4 Float32 AntennaScan_Tb_Array 0.5 3.0 Kelvin -9999.0
nedt_h Float32 AntennaScan_Tb_Array 0.5 3.0 Kelvin -9999.0
nedt_v Float32 AntennaScan_Tb_Array 0.5 3.0 Kelvin -9999.0
polarization_rotation_angle Float32 AntennaScan_Tb_Array 0.0 90.0 Degrees -9999.0
sea_ice_fraction Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
solar_direct_correction_h Float32 AntennaScan_Tb_Array 0.0 0.6 Kelvin -9999.0
solar_direct_correction_v Float32 AntennaScan_Tb_Array 0.0 0.6 Kelvin -9999.0
solar_direct_phi Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
solar_direct_theta Float32 AntennaScan_Tb_Array 0.0 180.0 Degrees -9999.0
solar_specular_correction_3 Float32 AntennaScan_Tb_Array -0.5 1.0 Kelvin -9999.0
solar_specular_correction_4 Float32 AntennaScan_Tb_Array -0.5 1.0 Kelvin -9999.0
solar_specular_correction_h Float32 AntennaScan_Tb_Array -0.5 1.0 Kelvin -9999.0
solar_specular_correction_v Float32 AntennaScan_Tb_Array -0.5 1.0 Kelvin -9999.0
solar_specular_lat Float32 AntennaScan_Tb_Array -90.0 90.0 Degrees -9999.0
solar_specular_lon Float32 AntennaScan_Tb_Array -180.0 179.999 Degrees -9999.0
solar_specular_phi Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
solar_specular_reflection_coefficient_h Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
solar_specular_reflection_coefficient_v Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
solar_specular_theta Float32 AntennaScan_Tb_Array 0.0 99.9 Degrees -9999.0
specular_declination Float32 AntennaScan_Tb_Array -90.0 90.0 Degrees -9999.0
specular_right_ascension Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
surface_water_fraction_mb_h Float32 AntennaScan_Tb_Array 0.0 1.0 N/A -9999.0
surface_water_fraction_mb_v Float32 Antena_Scan_Tb_Array 0.0 1.0 N/A -9999.0
ta_3 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
ta_4 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
ta_filtered_3 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
ta_filtered_4 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
ta_filtered_h Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
ta_filtered_v Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
ta_h Float32 AntennaScan_Tb_Array -0.0 340.0 Kelvin -9999.0
ta_v Float32 AntennaScan_Tb_Array -0.0 340.0 Kelvin -9999.0
tb_3 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
tb_4 Float32 AntennaScan_Tb_Array -50.0 -50.0 Kelvin -9999.0
tb_declination Float32 AntennaScan_Tb_Array -90.0 90.0 Degrees -9999.0
tb_h Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
tb_h_surface_corrected Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
tb_lat Float32 AntennaScan_Tb_Array -90 90 Degrees -9999.0
tb_lon Float32 AntennaScan_Tb_Array -180 179.999 Degrees -9999.0
tb_mode_flag Bit flag AntennaScan_Tb_Array N/A N/A N/A N/A
tb_qual_flag_3 Bit flag AntennaScan_Tb_Array N/A N/A N/A N/A
tb_qual_flag_4 Bit flag AntennaScan_Tb_Array N/A N/A N/A N/A
tb_qual_flag_h Bit flag AntennaScan_Tb_Array N/A N/A N/A N/A
tb_qual_flag_v Bit flag AntennaScan_Tb_Array N/A N/A N/A N/A
tb_right_ascension Float32 AntennaScan_Tb_Array 0.0 359.999 Degrees -9999.0
tb_time_seconds Float64 AntennaScan_Tb_Array 0.0 9.46E8 Seconds -9999.0
tb_time_utc Char AntennaScan_Tb_Array N/A N/A N/A -9999.0
tb_upwelling Float32 AntennaScan_Tb_Array 0.0 4.0 Kelvin -9999.0
tb_v Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
tb_v_surface_corrected Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
toa_3 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
toa_4 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
toa_h Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
toa_v Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
toi_3 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
toi_4 Float32 AntennaScan_Tb_Array -50.0 50.0 Kelvin -9999.0
toi_h Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
toi_v Float32 AntennaScan_Tb_Array 0.0 340.0 Kelvin -9999.0
wind_direction_ancillary Float32 AntennaScan_Tb_Array 0.0 359.999 degrees -9999.0
wind_speed_ancillary Float32 AntennaScan_Tb_Array 0.0 75.0 m/s -9999.0

Calibration_Data

Table A2 lists the elements in the Calibration Data group. The Calibration Data provides information about the instrument component losses and noise temperatures which the SMAP Level-1B brightness temperature data product employs in the calibration algorithm. Included are values for the vertical and horizontal polarization for the fullband. All of the product elements in the Calibration Data group are stored in a single HDF5 Group named Calibration_Data. A distinct HDF5 Dataset stores each data element. The name of each Dataset object matches the data element that it stores. Table A2 lists the elements in the Calibration Data group.

The data elements in the Calibration Data group have varying shapes depending on whether data is stored for both the vertical and horizontal channels. TheAntennaScan_VHPol_Array shape describes a two-dimensional array. The slowest moving dimension represents a particular antenna scan. The second dimension represents the polarization. The element that represents vertical polarization always precedes the element that represents horizontal polarization.

Table A2. Calibration Data Fields
Data Field Name Type Shape Valid_Min Valid_Max Units Fill/Gap Value
cal_loss12_radome Float32 AntennaScan_Array 1.0 2.0 N/A -9999.0
cal_loss1_reflector Float32 AntennaScan_VHPol_Array 1.0 2.0 N/A -9999.0
cal_loss2_feed Float32 HighResolutionScan_Subband_Array 1.0 2.0 N/A -9999.0
cal_loss3_omt Float32 HighResolutionScan_Subband_VHPol_Array  1.0 2.0 N/A -9999.0
cal_loss4_coupler Float32 HighResolutionScan_Subband_VHPol_Array 1.0 2.0 N/A -9999.0
cal_loss5_diplexer Float32 HighResolutionScan_Subband_VHPol_Array 1.0 2.0 N/A -9999.0
cal_nd_phase Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0
cal_rx_phase Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0
cal_temp12_radome Float32 AntennaScan_Array 110.0 260.0 Kelvin -9999.0
cal_temp1_reflector Float32 AntennaScan_Array 330.0 400.0 Kelvin -9999.0
cal_temp2_feed Float32 AntennaScan_Array 253.15 313.15 Kelvin -9999.0
cal_temp3_omt Float32 AntennaScan_VHPol_Array 253.15 313.15 Kelvin -9999.0
cal_temp4_coupler Float32 AntennaScan_VHPol_Array 253.15 313.15 Kelvin -9999.0
cal_temp5_deplexer Float32 AntennaScan_VHPol_Array 253.15 313.15 Kelvin -9999.0
cal_temp_nd Float32 HighResolutionScan_Subband_Array  253.15 313.15 Kelvin -9999.0
cal_temp_ref Float32 AntennaScan_VHPol_Array 253.15 313.15 Kelvin -9999.0
cal_temp_xnd Float32 HighResolutionScan_Subband_Array  -253.15 314.15 Kelvin -9999.0
cal_tempref_offset Float32 HighResolutionScan_Subband_VHPol_Array  -1.0 1.0 Kelvin -9999.0
cal_tnd Float32 HighResolutionScan_Subband_VHPol_Array  218.0 658.0 Kelvin -9999.0
cal_tref Float32 HighResolutionScan_Subband_VHPol_Array 252.15 314.15 Kelvin -9999.0
cal_txnd Float32 HighResolutionScan_Subband_VHPol_Array  62.0 216.0 Kelvin -9999.0
cal_xnd_phase  Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0

High_Resolution_Calibration_Data 

Table A3 lists the elements in the High Resolution Calibration Data group. The High Resolution Calibration Data provides information about the instrument component losses and noise temperatures which the SMAP Level-1B brightness temperature data product employs in the calibration algorithm. Included are values for the vertical and horizontal polarization for all 16 subbands. All of the product elements in the High Resolution Calibration Data group are stored in a single HDF5 Group named HighResolution_Calibration_Data. A distinct HDF5 data set stores each data element. The name of each data set object matches the data element that it stores. Table A3 lists the elements in the High Resolution Calibration Data group.

The data elements in the High Resolution Calibration Data group have varying shapes depending on whether data is stored for both the vertical and horizontal channels. The HighResolutionScan_Subband_VHPol_Array shape describes a three-dimensional array. The slowest moving dimension represents a particular antenna scan. The second dimension represents the 16 subbands. The third dimension represents the polarization. The element that represents vertical polarization always precedes the element that represents horizontal polarization.

Table A3. High Resolution Calibration Data Fields
Data Field Name Type Shape Valid_Min Valid_Max Units Fill/Gap Value
cal_loss2_feed16 Float32 HighResolutionScan_Subband_Array 1.0 2.0 N/A -9999.0
cal_loss3_omt16  Float32 HighResolutionScan_Subband_VHPol_Array  1.0 2.0 N/A -9999.0
cal_loss4_coupler16 Float32 HighResolutionScan_Subband_VHPol_Array  1.0 2.0 N/A -9999.0
cal_loss5_diplexer16 Float32 HighResolutionScan_Subband_VHPol_Array 1.0 2.0 N/A -9999.0
cal_nd_phase16 Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0
cal_rx_phase16 Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0
cal_temp_nd16  Float32 HighResolutionScan_Subband_Array  253.15 313.15 Kelvin -9999.0
cal_temp_xnd16 Float32 HighResolutionScan_Subband_Array  253.15 313.15 Kelvin -9999.0
cal_tempref_offset16 Float32 HighResolutionScan_Subband_VHPol_Array  1.0 1.0 Kelvin -9999.0
cal_tnd16  Float32 HighResolutionScan_Subband_VHPol_Array  212.0 676.0 Kelvin -9999.0
cal_tref16  Float32 HighResolutionScan_Subband_VHPol_Array 252.15 314.15 Kelvin -9999.0
cal_txnd16 Float32 HighResolutionScan_Subband_VHPol_Array  61.0 217.1 Kelvin -9999.0
cal_xnd_phase16 Float32 HighResolutionScan_Subband_Array  -3.1415927 3.1415927 Radians -9999.0
calibration_time_seconds Float64 HighResolutionScan_Array -0.0 9.46E8 Seconds -9999.0
highresolution_scan_index Uint32 HighResolutionScan_Array 0 800 N/A -9999.0

Spacecraft_Data 

Tables A4 describes the data fields within the HDF5 Group called Spacecraft_Data. All the HDF5 data sets in the Spacecraft Data group have AntennaScan_Array shape. TheAntennaScan_Array shape describes a one-dimensional array, where each array element represents one rotation of the SMAP antenna. The representative time instant for each antenna scan takes place when the antenna boresight aligns with the X-axis of the SMAP spacecraft coordinate system. The X-axis of the spacecraft coordinate system approximates the direction of motion of the SMAP spacecraft. Thus, array element x_pos(212) lists the representative spacecraft position in the x dimension, array elementyaw(212) lists the representative spacecraft yaw, and array element sc_geodetic_alt(212) lists the representative spacecraft altitude at the instant during each antenna scan when the boresight aligns with the X-axis of the spacecraft coordinate system. The time of that event appears in array element antenna_scan_time_utc (212). The precise range of time covered by each antenna scan depends on the antenna rotation rate. The mission selected one of two likely antenna rotation rates. They are either 14.6 revolutions per minute or 13 revolutions per minute.

Table A4. Spacecraft Data Fields
Data Field Name Type Shape Valid Min

Valid Max

Unit Fill/Gap Value
antenna_scan_mode_flag Uint16 AntennaScan_Array 0 65535 N/A 65534
antenna_scan_qual_flag Uint16 AntennaScan_Array N/A N/A N/A 65534
antenna_scan_time Float64 AntennaScan_Array 0.0 9.46E8 seconds -9999.0
antenna_scan_time_utc FixedLenString 
(24 characters)
AntennaScan_Array 2014-10-31T00:00:00.000Z 2030-12-31T23:59:60.999Z N/A N/A
footprints_per_scan Uint16 AntennaScan_Array 0 300 N/A 65534
pitch Float32 AntennaScan_Array -90.0 90.0 degrees -9999.0
roll Float32 AntennaScan_Array -90.0 90.0 degrees -9999.0
sc_alongtrack_velocity Float32 AntennaScan_Array -8000.0 8000.0 m/s -9999.0
sc_geodetic_alt_ellipsoid Float32 AntennaScan_Array 650000.0 900000.0 meters -9999.0
sc_nadir_angle Float32 AntennaScan_Array 0.0 180.0 degrees -9999.0
sc_nadir_lat Float32 AntennaScan_Array -90 90 degrees -9999.0
sc_nadir_lon Float32 AntennaScan_Array -180 179.999 degrees -9999.0
sc_radial_velocity Float32 AntennaScan_Array -8000.0 8000.0 m/s -9999.0
tbs_per_scan Uint16 AntennaScan_Array 0 300 N/A 65534
x_pos Float32 AntennaScan_Array -999999.0 9999999.0 m -9999.0
x_vel Float32 AntennaScan_Array -8000.0 8000.0 m/s -9999.0
y_pos Float32 AntennaScan_Array -999999.0 9999999.0 m -9999.0
y_vel Float32 AntennaScan_Array -8000.0 8000.0 m/s -9999.0
yaw Float32 AntennaScan_Array -180.0 180.0 degrees -9999.0
z_pos Float32 AntennaScan_Array -999999.0 9999999 m -9999.0
z_vel Float32 AntennaScan_Array -8000.0 8000.0 m/s -9999.0

Data Field Definitions

antenna_earth_azimuth

The is angle from due North to the projection of the antenna scan angle onto a plane tangent to the Earth at the spacecraft nadir point.  The spacecraft nadir point serves as the vertex of this angle.

antenna_look_angle

The angle defined by the antenna boresight vector and the spacecraft nadir vector.

antenna_scan_angle

The angle in the X-Y plane of the instrument fixed coordinate system that indicates the angular position of the antenna assembly. The angle is measured in the counterclockwise direction from the X axis, which approximates the direction of motion of the spacecraft.

antenna_sidelobe_correction_3

TB correction to TA for earth sidelobe contribution for 3rd Stokes.

antenna_sidelobe_correction_4

TB correction to TA for earth sidelobe contribution for 4th Stokes.

antenna_sidelobe_correction_h

TB correction to TA for earth sidelobe contribution for horizontal polarization.

antenna_sidelobe_correction_v

TB correction to TA for earth sidelobe contribution for vertical polarization.

atm_correction_h

TB correction to TA for atmospheric emission for horizontal polarization.

atm_correction_v

TB correction to TA for atmospheric emission for vertical polarization.

atm_loss

The reduction in power density of the brightness temperature signal as it propagates through the Earth's atmosphere.

earth_boresight_azimuth

The angle defined by the vector that extends from the intersection of the spacecraft geodetic nadir vector on the Earth's surface to geographic North and the vector that extends from the intersection of the spacecraft geodetic nadir on the Earth's surface to the pierce point of the boresight vector. The angle measure is clockwise from the northward vector.

earth_boresight_incidence

The angle defined by the antenna boresight vector and the mean surface normal vector.

faraday_rotation_angle

The Faraday rotation angle. 

faraday_rotation_correction_h

TB correction to TA for Faraday Rotation for horizontal polarization.

faraday_rotation_correction_v

TB correction to TA for Faraday Rotation for vertical polarization.

footprint_surface_status
Indicates if the footprint center lies on land (0) or water (1).

galactic_direct_correction_h

TB correction to TA for direct galactic contamination for horizontal polarization.

galactic_direct_correction_v

TB correction to TA for direct galactic contamination for vertical polarization.

galactic_reflected_correction_3

The brightness temperature correction to the antenna temperature, TA, for reflected galactic and cosmic contamination to derive tb_3. the galactic_reflected_correction_3 field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

galactic_reflected_correction_4

TB correction to TA for reflected galactic contamination for 4th Stokes.

galactic_reflected_correction_h

TB correction to TA for reflected galactic contamination for horizontal polarization.

galactic_reflected_correction_v

TB correction to TA for reflected galactic contamination for vertical polarization.

lunar_direct_phi

The angle defined by the +X axis of the Antenna Beam Frame Coordinate System and the vector that extends from the origin to the Moon projected onto the XY plane of the Antenna Beam Frame Coordinate System.

lunar_direct_theta

The angle defined by the +Z axis of the Antenna Beam Frame Coordinate System, which is equivalent to the electrical boresight vector, and the vector that extends from the origin of the Antenna Bean Frame Coordinate System to the Moon.

lunar_specular_correction_3

TB correction to TA for reflected lunar contamination for 3rd Stokes.

lunar_specular_correction_4

TB correction to TA for reflected lunar contamination for 4th Stokes.

lunar_specular_correction_h

TB correction to TA for reflected lunar contamination for horizontal polarization.

lunar_specular_correction_v

TB correction to TA for reflected lunar contamination for vertical polarization.

lunar_specular_lat

 Latitude of the center of the lunar specular reflection point on the Earth's surface relative to the spacecraft position.

lunar_specular_lon

Longitude of the center of the lunar specular reflection point on the Earth's surface relative to the spacecraft position.

lunar_specular_phi

The angle defined by the +X axis of the Antenna Beam Frame Coordinate System and the vector that extends from the origin to the lunar glint spot on the Earth's surface projected onto the XY plane of the Antenna Beam Frame Coordinate System.

lunar_specular_reflection_coefficient_h

Reflection coefficient of surface at lunar specular point for horizontal polarization.

lunar_specular_reflection_coefficient_v

Reflection coefficient of surface at lunar specular point for vertical polarization.

lunar_specular_theta

The angle defined by the +Z axis of the Antenna Beam Frame Coordinate System, which is equivalent to the electrical boresight vector, and the vector that extends from the origin of the Antenna Bean Frame Coordinate System to the lunar glint spot on the Earth's surface.

nedt_3

NEDT after RFI removal for third Stokes.

nedt_4

NEDT after RFI removal for fourth Stokes. See Table A5 for more details.

Table A5. Description of tb_qual_flag_v
Bits Interpretation Value Description
0 Vertical polarization quality flag 0 Vertical polarization brightness temperature measurement has acceptable quality
1 Use of vertical polarization brightness temperature not recommended
1 Vertical polarization range flag 0 Vertical polarization brightness temperature measurement falls in expected range
1 Vertical polarization brightness temperature value is out of range
2

Vertical polarization RFI detection flag 0 RFI not detected for vertical polarization brightness temperatures in the grid cell
1 If RFI was detected, the software was unable to correct the vertical polarization brightness temperature for RFI
3

Vertical polarization RFI correction flag 0 If RFI was detected, the vertical polarization brightness temperature was corrected to remove RFI
1 If RFI was detected, the software was unable to correct the vertical polarization brightness temperature for RFI
4

Vertical polarization NEDT flag 0 Vertical polarization brightness temperature measurement has acceptable NEDT
1 Use of vertical polarization brightness temperature not recommended, since NEDT exceeds pre-determined threshold
5

Vertical polarization direct sun correction 0 Correction for direct sun operated successfully on the vertical polarization brightness temperature
1 Correction for direct sun did not function or yielded poor results on the vertical polarization brightness temperature
6

Vertical polarization reflected sun correction 0 Correction for reflected sun operated successfully on the vertical polarization brightness temperature
1 Correction for reflected sun did not function or yielded poor results on the vertical polarization brightness temperature
7

Vertical polarization reflected moon correction 0 Correction for reflected moon operated successfully on the vertical polarization brightness temperature
1 Correction for reflected moon did not function or yielded poor results on the vertical polarization brightness temperature
8

Vertical polarization direct galaxy correction 0 Correction for direct galaxy operated successfully on the vertical polarization brightness temperature
1 Correction for direct galaxy did not function or yielded poor results on the vertical polarization brightness temperature
9

Vertical polarization reflected galaxy correction 0 Correction for reflected galaxy operated successfully on the vertical polarization brightness temperature
1 Correction for reflected galaxy did not function or yielded poor results on the vertical polarization brightness temperature
10 Vertical polarization correction for atmospheric conditions 0 Correction for atmospheric conditions operated successfully on the vertical polarization brightness temperature
1 Correction for atmospheric conditions did not function or yielded poor results on the vertical polarization brightness temperature
11 Vertical polarization Faraday rotation correction 0 Correction for Faraday rotation operated successfully on the vertical polarization brightness temperature
1 Correction for Faraday rotation did not function or yielded poor results on the vertical polarization brightness temperature
12 Vertical polarization null value 0 The corresponding vertical polarization brightness temperature element contains a calculated value.
1 The corresponding vertical polarization brightness temperature element is null.
13-15 Undefined N/A N/A
N/A N/A
nedt_h

NEDT after RFI removal for horizontal polarization.

nedt_v

NEDT after RFI removal for vertical polarization.

polarization_rotation_angle

The angle between the plane of polarization and the reference plane used to calculate the Stokes vector. The polarization_rotation_angle field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

sea_ice_fraction

 The angle between the plane of polarization and the reference plane used to calculate the Stokes vector.

solar_direct_correction_h

TB correction to TA for direct solar contamination for horizontal polarization.  Limits for all error sources contributions will be determined with the orbit simulator

solar_direct_correction_v

TB correction to TA for direct solar contamination for vertical polarization.  Limits for all error sources contributions will be determined with the orbit simulator

solar_direct_phi

The angle defined by the +X axis of the Antenna Beam Frame Coordinate System and the vector that extends from the origin to the Sun projected onto the XY plane of the Antenna Beam Frame Coordinate System.

solar_direct_theta

The angle defined by the +Z axis of the Antenna Beam Frame Coordinate System, which is equivalent to the electrical boresight vector, and the vector that extends from the origin of the Antenna Bean Frame Coordinate System to the Sun.

solar_specular_correction_3

TB correction to TA for reflected solar contamination for 3rd Stokes.

solar_specular_correction_4

TB correction to TA for reflected solar contamination for 4th Stokes.

solar_specular_correction_h

TB correction to TA for reflected solar contamination for horizontal polarization.

solar_specular_correction_v

TB correction to TA for reflected solar contamination for vertical polarization.

solar_specular_lat

The geodetic latitude of the center of the solar specular reflection point on the Earth's surface relative to the spacecraft position. The solar_specular_lat field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

solar_specular_lon

The longitude of the center of the solar specular reflection point on the Earth's surface relative to the spacecraft position. The solar_specular_lon field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

solar_specular_phi

The angle defined by the +X axis of the ABFCS and the vector that extends from the origin to the solar glint spot on the Earth's surface projected onto the XY plane of the ABFCS. The solar_specular_phi field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

solar_specular_reflection_coefficient_h

Reflection coefficient of surface at solar specular point for horizontal polarization.

solar_specular_reflection_coefficient_v

Reflection coefficient of surface at solar specular point for vertical polarization.

solar_specular_theta

The angle defined by the +Z axis of the Antenna Beam Frame Coordinate System, which is equivalent to the electrical boresight vector, and the vector that extends from the origin of the Antenna Bean Frame Coordinate System to the solar glint spot on the Earth's surface.

specular_declination

Declination of the specular reflection vector relative to each footprint in the product.  The specular reflection vector is in the same plane as the boresight vector and the spacecraft nadir vector.

specular_right_ascension

Right ascension of the specular reflection vector relative to each footprint in the product.  The specular reflection vector is in the same plane as the boresight vector and the spacecraft nadir vector.

surface_water_fraction_mb_h

Areal fraction of static water within the radiometer H pol antenna pattern.

surface_water_fraction_mb_v

Areal fraction of static water within the radiometer V pol antenna pattern.

ta_3

The antenna temperature for the 3rd Stokes parameter before RFI filtering. 

ta_4

The antenna temperature for the 4th Stokes parameter before RFI filtering.

ta_filtered_3

Antenna temperature for the 3rd Stokes parameter after RFI filtering. 

ta_filtered_4

Antenna temperature for the 4th Stokes parameter after RFI filtering. 

ta_filtered_h

Horizontally polarized antenna temperature after RFI filtering

ta_filtered_v

Vertically polarized antenna temperature after RFI filtering.

ta_h

The horizontally polarized antenna temperature before RFI filtering. 

ta_v

The vertically polarized antenna temperature before RFI filtering.

tb_3

The 3rd Stokes parameter at the surface of the Earth after RFI filtering. The tb_4 field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

tb_4

The 4th Stokes parameter at the surface of the Earth after RFI filtering. 

tb_declination

The declination of the spacecraft boresight vector. 

tb_h

The horizontally polarized brightness temperature at the surface of the Earth after RFI filtering. 

b_h_surface_corrected

The horizontally polarized water/land contamination corrected brightness temperature at the surface of the Earth after RFI filtering. This value represents the corrected land brightness temperature if footprint_surface_status is “0” or represents the corrected water brightness temperature if footprint_surface_status is “1.”

tb_lat

Latitude of the intersection of the antenna boresight vector and the Earth's surface.

tb_lon

Longitude of the intersection of the antenna boresight vector and the Earth's surface.

tb_mode_flag

Bit flags that indicate instrument and ambient conditions when the brightness temperature measurements were acquired. The tb_mode_flag field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan. See Table A6 for more details.

Table A6. Description of tb_mode_flag
Bits Interpretation Value Description
0 Data resolution flag (land/ocean) 0 High resolution data contribute to this scan
1 Low resolution data contribute to this scan
1 Scan view flag 0 Brightness temperature footprint is forward of spacecraft position
1 Brightness temperature footprint is aft of spacecraft position
2

Spacecraft viewing mode 0 Instrument is in normal Earth viewing mode
1 Instrument boresight does not view the Earth's surface
3

Ocean calibration region 0 Pixel views external calibration region over the ocean
1 Pixel does not view ocean calibration region over the ocean
4

Antarctic calibration region 0 Correction for reflected sun operated successfully on the 4th Stokes parameter
1 Correction for reflected sun did not function or yielded poor results on the 4th Stokes parameter
5

Lunar visible flag 0 The moon is not visible from the SMAP spacecraft.
1 The moon is visible from the SMAP spacecraft.
6

Solar visible flag 0 The sun is not visible from the SMAP spacecraft.
1 The sun is visible from the SMAP spacecraft.
7-15 Undefined N/A N/A
N/A N/A
tb_qual_flag_3

Bit flags that indicate the quality of the 3rd Stokes parameter. The tb_qual_flag_3 field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan. See Table A7 for more details.

Table A7. Description of tb_qual_flag_3
Bits Interpretation Value Description
0 3rd Stokes quality flag 0 3rd Stokes parameter measurement has acceptable quality
1 Use of 3rd Stokes parameter measurement not recommended
1 3rd Stokes range flag 0 3rd Stokes parameter measurement falls in expected range
1 3rd Stokes parameter measurement is out of range
2

3rd Stokes RFI detection flag 0 RFI not detected for 3rd Stokes brightness temperatures in the grid cell
1 RFI detected for 3rd Stokes brightness temperatures in the grid cell
3

3rd Stokes RFI correction flag 0 If RFI was detected, the 3rd Stokes brightness temperature was corrected to remove RFI
1 If RFI was detected, the software was unable to correct the 3rd Stokes brightness temperature for RFI
4

3rd Stokes NEDT flag 0 3rd Stokes has acceptable NEDT
1 Use of 3rd Stokes not recommended, since NEDT exceeds pre-determined threshold
5

3rd Stokes direct sun correction 0 Correction for direct sun operated successfully on the 3rd Stokes parameter
1 Correction for direct sun did not function or yielded poor results on the 3rd Stokes parameter
6

3rd Stokes reflected sun correction 0 Correction for reflected sun operated successfully on the 3rd Stokes parameter
1 Correction for reflected sun did not function or yielded poor results on the 3rd Stokes parameter
7

3rd Stokes reflected moon correction 0 Correction for reflected moon operated successfully on the 3rd Stokes parameter
1 Correction for reflected moon did not function or yielded poor results on the 3rd Stokes parameter
8

3rd Stokes direct galaxy correction 0 Correction for direct galaxy operated successfully on the 3rd Stokes parameter
1 Correction for direct galaxy did not function or yielded poor results on the 3rd Stokes parameter
9

3rd Stokes reflected galaxy correction 0 Correction for reflected galaxy operated successfully on the 3rd Stokes parameter
1 Correction for reflected galaxy did not function or yielded poor results on the 3rd Stokes parameter
10 3rd Stokes correction for atmospheric conditions 0 Correction for atmospheric conditions operated successfully on the 3rd Stokes parameter
1 Correction for atmospheric conditions did not function or yielded poor results on the 3rd Stokes parameter
11 Undefined N/A N/A
N/A N/A
12 3rd Stokes null value 0 The corresponding 3rd Stokes parameter element contains a calculated value.
1 The corresponding 3rd Stokes parameter element is null.
13-15 Undefined N/A N/A
N/A N/A
tb_qual_flag_4

Bit flags that indicate the quality of the 4th Stokes parameter. The tb_qual_flag_4 field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan. See Table A8 for more details.

Table A8. Description of tb_qual_flag_4
Bits Interpretation Value Description
0 4th Stokes quality flag 0 4th Stokes parameter measurement has acceptable quality
1 Use of 4th Stokes parameter measurement not recommended
1 4th Stokes range flag 0 4th Stokes parameter measurement falls in expected range
1 4th Stokes parameter measurement is out of range
2

4th Stokes RFI detection flag 0 RFI not detected for 4th Stokes brightness temperatures in the grid cell
1 RFI detected for 4th Stokes brightness temperatures in the grid cell
3

4th Stokes RFI correction flag 0 If RFI was detected, the 4th Stokes brightness temperature was corrected to remove RFI
1 If RFI was detected, the software was unable to correct the 4th Stokes brightness temperature for RFI
4

4th Stokes NEDT flag 0 4th Stokes has acceptable NEDT
1 Use of 4th Stokes not recommended, since NEDT exceeds pre-determined threshold
5

4th Stokes direct sun correction 0 Correction for direct sun operated successfully on the 4th Stokes parameter
1 Correction for direct sun did not function or yielded poor results on the 4th Stokes parameter
6

4th Stokes reflected sun correction 0 Correction for reflected sun operated successfully on the 4th Stokes parameter
1 Correction for reflected sun did not function or yielded poor results on the 4th Stokes parameter
7

4th Stokes reflected moon correction 0 Correction for reflected moon operated successfully on the 4th Stokes parameter
1 Correction for reflected moon did not function or yielded poor results on the 4th Stokes parameter
8

4th Stokes direct galaxy correction 0 Correction for direct galaxy operated successfully on the 4th Stokes parameter
1 Correction for direct galaxy did not function or yielded poor results on the 4th Stokes parameter
9

4th Stokes reflected galaxy correction 0 Correction for reflected galaxy operated successfully on the 4th Stokes parameter
1 Correction for reflected galaxy did not function or yielded poor results on the 4th Stokes parameter
10 4th Stokes correction for atmospheric conditions 0 Correction for atmospheric conditions operated successfully on the 4th Stokes parameter
1 Correction for atmospheric conditions did not function or yielded poor results on the 4th Stokes parameter
11 Undefined N/A N/A
N/A N/A
12 4th Stokes null value 0 The corresponding 4th Stokes parameter element contains a calculated value.
1 The corresponding 4th Stokes parameter element is null.
13-15 Undefined N/A N/A
N/A N/A
tb_qual_flag_h

Bit flags that indicate the quality of the horizontally polarized brightness temperature. The tb_qual_flag_h field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan. See Table A9 for more details.

Table A9. Description of tb_qual_flag_h
Bits Interpretation Value Description
0 Horizontal polarization quality flag 0 Horizontal polarization brightness temperature measurement has acceptable quality
1 Use of horizontal polarization brightness temperature not recommended
1 Horizontal polarization range flag 0 Horizontal polarization brightness temperature measurement falls in expected range
1 Horizontal polarization brightness temperature value is out of range
2

Horizontal polarization RFI detection flag 0 RFI not detected for Horizontal polarization brightness temperatures in the grid cell
1 If RFI was detected, the software was unable to correct the horizontal polarization brightness temperature for RFI
3

Horizontal polarization RFI correction flag 0 If RFI was detected, the horizontal polarization brightness temperature was corrected to remove RFI
1 If RFI was detected, the software was unable to correct the horizontal polarization brightness temperature for RFI
4

Horizontal polarization NEDT flag 0 Horizontal polarization brightness temperature measurement has acceptable NEDT
1 Use of horizontal polarization brightness temperature not recommended, since NEDT exceeds pre-determined threshold
5

Horizontal polarization direct sun correction 0 Correction for direct sun operated successfully on the horizontal polarization brightness temperature
1 Correction for direct sun did not function or yielded poor results on the horizontal polarization brightness temperature
6

Horizontal polarization reflected sun correction 0 Correction for reflected sun operated successfully on the horizontal polarization brightness temperature
1 Correction for reflected sun did not function or yielded poor results on the horizontal polarization brightness temperature
7

Horizontal polarization reflected moon correction 0 Correction for reflected moon operated successfully on the horizontal polarization brightness temperature
1 Correction for reflected moon did not function or yielded poor results on the horizontal polarization brightness temperature
8

Horizontal polarization direct galaxy correction 0 Correction for direct galaxy operated successfully on the horizontal polarization brightness temperature
1 Correction for direct galaxy did not function or yielded poor results on the horizontal polarization brightness temperature
9

Horizontal polarization reflected galaxy correction 0 Correction for reflected galaxy operated successfully on the horizontal polarization brightness temperature
1 Correction for reflected galaxy did not function or yielded poor results on the horizontal polarization brightness temperature
10 Horizontal polarization correction for atmospheric conditions 0 Correction for atmospheric conditions operated successfully on the horizontal polarization brightness temperature
1 Correction for atmospheric conditions did not function or yielded poor results on the horizontal polarization brightness temperature
11 Horizontal polarization Faraday rotation correction 0 Correction for Faraday rotation operated successfully on the horizontal polarization brightness temperature
1 Correction for Faraday rotation did not function or yielded poor results on the horizontal polarization brightness temperature
12 Horizontal polarization null value 0 The corresponding horizontal polarization brightness temperature element contains a calculated value.
1 The corresponding horizontal polarization brightness temperature element is null.
13-15 Undefined N/A N/A
N/A N/A
tb_qual_flag_v

Bit flags that indicate the quality of the vertically polarized brightness temperature.

tb_right_ascension

Right ascension of the spacecraft boresight vector.

tb_time_seconds

J2000 time when brightness temperatures were recorded in seconds.

tb_time_utc

UTC time when brightness temperatures were recorded.

tb_upwelling

The component of the top of the atmosphere apparent brightness temperature that is due to upwelling thermal radiation of the atmosphere. The tb_upwelling field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dime nsion index represents each of the footprints in the scan.

tb_v

The vertically polarized brightness temperature at the surface of the Earth after RFI filtering. The tb_v field is a two-dimensional array. The slower moving dimension index represents the antenna scan. The faster moving dimension index represents each of the footprints in the scan.

tb_v_surface_corrected
The vertically polarized water/land contamination corrected brightness temperature at the surface of the Earth after RFI filtering. This value represents the corrected land brightness temperature if footprint_surface_status is “0” or represents the corrected water brightness temperature if footprint_surface_status is “1.”

toa_3

The apparent 3rd Stokes parameter at the top of the atmosphere.  The top of atmosphere is equivalent to the bottom of the ionosphere.

toa_4

 The apparent 4th Stokes parameter at the top of the atmosphere.  The top of atmosphere is equivalent to the bottom of the ionosphere.

toa_h

The horizontally polarized apparent brightness temperature at the top of the atmosphere.  The top of atmosphere is equivalent to the bottom of the ionosphere.

toa_v

The vertically polarized apparent brightness temperature at the top of the atmosphere.  The top of atmosphere is equivalent to the bottom of the ionosphere.

toi_3

Apparent 3rd Stokes parameter at the top of the ionosphere.

toi_4

Apparent 4th Stokes parameter at the top of the ionosphere.

toi_h

 Horizontally polarized apparent brightness temperature at the top of the ionosphere.

toi_v

 Vertically polarized apparent brightness temperature at the top of the ionosphere.

wind_direction_ancillary
The interpolated direction of sea surface winds at the center of the corresponding Tb.  Wind direction is measured as the clockwise rotation from local North (meteorological convention). Wind measurements are based on data provided by the National Centers for Environmental Prediction (NCEP) of the National Oceanographic and Atmospheric Administration (NOAA). 

wind_speed_ancillary
The interpolated speed of sea surface winds at the center of the corresponding Tb.  Wind measurements are based on data provided by the National Centers for Environmental Prediction (NCEP) of the National Oceanographic and Atmospheric Administration (NOAA).

cal_loss12_radome

Calibration model lumped loss factor of radome (stored V then H).

cal_loss1_reflector

Calibration model lumped loss factor of reflector (stored V then H).

cal_loss2_feed

Calibration model lumped loss factor of feed.

cal_loss3_omt

Calibration model lumped loss factor of OMT (stored V then H).

cal_loss4_coupler

Calibration model lumped loss factor of coupler (stored V then H).

cal_loss5_diplexer

Calibration model lumped loss factor of the diplexer (stored V then H).

cal_nd_phase

The calibration model noise diode phase applied in the calibration of fullband data. The cal_nd_phase field is a one dimensional array with one value for each antenna scan.

cal_rx_phase

The calibration model receiver phase for calibration of radiometer fullband data. The cal_rx_phase16 field is a one dimensional array with one value for each antenna scan.

cal_temp12_radome

Calibration model, physical temperature, radome (same for V and H as the radome temp will most likely act on the 2 polarizations in the same way).

cal_temp1_reflector

Calibration model, physical temperature, reflector (same for V and H as the reflector temp will most likely act on the 2 polarizations in the same way).

cal_temp2_feed

Calibration model, physical temperature, feed.

cal_temp3_omt

Calibration model, physical temperature, OMT (stored V then H).

cal_temp4_coupler

Calibration model, physical temperature, coupler (stored V then H).

cal_temp5_deplexer

Calibration model, physical temperature, diplexer (stored V then H).

cal_temp_nd

Calibration model, physical temperature, noise diode.

cal_temp_ref

Calibration model, physical temperature, reference (stored V then H).

cal_temp_xnd

Calibration model, physical temperature, external noise diode.

cal_tempref_offset

Calibration model, physical temperature offset, reference (stored V then H).

cal_tnd

Calibration model, brightness temperature, noise diode (stored V then H).

cal_tref

Calibration model, brightness temperature, reference (stored V then H).

cal_txnd

Calibration model, brightness temperature, external noise diode (stored V then H).

cal_xnd_phase

Calibration model, external noise diode phase.

cal_loss2_feed16

Calibration model lumped loss factor of feed, 16 subbands.

cal_loss3_omt16

Calibration model lumped loss factor of OMT (stored V then H), 16 subbands.

cal_loss4_coupler16

Calibration model lumped loss factor of coupler (stored V then H), 16 subbands.

cal_loss5_diplexer16

Calibration model lumped loss factor of the diplexer (stored V then H), 16 subbands.

cal_nd_phase16

 Calibration model, noise diode phase, 16 subbands.

cal_rx_phase16

 Calibration model, receiver phase, 16 subbands.

cal_temp_nd16

Calibration model, physical temperature, noise diode, 16 subbands.

cal_temp_xnd16

Calibration model, physical temperature, external noise diode, 16 subbands.

cal_tempref_offset16

Calibration model, physical temperature offset, reference (stored V then H), 16 subbands.

cal_tnd16

Calibration model, brightness temperature, reference (stored V then H), 16 subbands.

cal_tref16

Calibration model, brightness temperature, external noise diode (stored V then H), 16 subbands.

cal_txnd16

Calibration model, brightness temperature, external noise diode (stored V then H), 16 subbands.

cal_xnd_phase16

Calibration model, external noise diode phase, 16 subbands.

calibration_time_seconds

Number of seconds since midnight on 1/1/1993 for each antenna rotation interpolated to antenna boresight azimuth of 0 degrees.

highresolution_scan_index

An array of indices of the high resolution antenna scan rotations in the current granule.  The value in this array references in the matching index in the Antenna Scan array.

antenna_scan_mode_flag

Operational mode of attitude/ephemeris telemetry and associated calculations at each instance when antenna boresight azimuth is 0 degrees. See Table A10 for more details.

Bits Interpretation Value Description
Table A10. Description of antenna_scan_mode_flag
0 Instrument viewing mode 0 Spacecraft antenna is positioned so that the SMAP instrument views locations on the Earth's surface.
1 Spacecraft antenna is positioned so that the SMAP instrument does not view the Earth. SMAP spacecraft is either in maneuver, running a cold sky calibration for the radiometer or in transition state.
1 Ephemeris Usage Flag 0 Processing employed reconstructed ephemeris
1 Processing employed predicted ephemeris
2 Data Resolution Flag 0 High resolution data contribute to this scan
1 Low resolution data contribute to this scan
3 Eclipse Flag 0 The SMAP spacecraft is not in eclipse. The Sun is visible from the SMAP spacecraft.
1 The SMAP spacecraft is in eclipse. The Sun is not visible from the SMAP spacecraft.
4-15 Undefined N/A N/A
N/A N/A
antenna_scan_qual_flag

Quality of attitude/ephemeris telemetry and associated calculations at each instance when antenna boresight azimuth is 0 degrees. The antenna_scan_qual_flag is a one-dimensional array. Each array index is representative of a specific antenna scan. See Table A11 for more details.

Table A11. Description of antenna_scan_qual_flag
Bits Interpretation Value Description
0 Ephemeris Quality 0 Quality and frequency of the ephemeris data is within acceptable range.
1 Quality or frequency of the ephemeris data may not be adequate to yield an accurate measure of spacecraft location.
1 Attitude Quality 0 Quality and frequency of the attitude data is within acceptable range.
1 Quality or frequency of the attitude data may not be adequate to yield an acceptable measure of spacecraft orientation.
2

Antenna Pointing Quality 0 Quality and frequency of the antenna pointing data is within acceptable range.
1 Quality or frequency of the antenna pointing data may not be adequate to yield an acceptable measure of antenna position.
3 Spacecraft half orbit location 0 All of the footprints associated with this spacecraft orbit location lie within the half orbit specified in the file name.
1 Some or all of the footprints associated with this spacecraft orbit location lie outside of the half orbit specified in the file name.
4-15 Undefined N/A N/A
N/A N/A
antenna_scan_time

Number of seconds in the J2000 epoch for each antenna rotation interpolated to antenna scan angle of 0 degrees.

antenna_scan_time_utc

UTC time stamp for each antenna rotation when antenna scan angle is 0 degrees.

footprints_per_scan

Number of brightness temperature footprints acquired in the current scan.

pitch

SC pitch interpolated to antenna scan angle of 0 degrees.

roll

SC roll interpolated to antenna scan angle of 0 degrees.

sc_alongtrack_velocity

Spacecraft velocity in the direction of the spacecraft orbital track interpolated to antenna scan angle of 0 degrees.

sc_geodetic_alt_ellipsoid

Spacecraft altitude above Earth WGS84 reference ellipsoid along the nadir track interpolated to antenna scan angle of 0 degrees.

sc_nadir_angle

 The angle defined by the spacecraft geodetic nadir vector and the negative Z axis of the spacecraft coordinate system at each instance when the antenna scan angle is 0 degrees.

sc_nadir_lat

Spacecraft latitude along nadir track interpolated to antenna scan angle of 0 degrees.

sc_nadir_lon

Spacecraft longitude along nadir track interpolated to antenna scan angle of 0 degrees.

sc_radial_velocity

Spacecraft velocity in the direction of the radius of the orbital track. Velocity that records change in altitude.

tbs_per_scan

Number of brightness temperature footprints acquired in the current scan.

x_pos

SC position in x direction of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

x_vel

SC velocity in x direction  of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

y_pos

SC position in y direction  of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

y_vel

SC velocity in y direction  of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

yaw

SC yaw interpolated to antenna scan angle of 0 degrees.

z_pos

SC position in z direction  of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

z_vel

SC velocity in z direction  of Earth Centered Rotating system interpolated to antenna scan angle of 0 degrees.

Fill/Gap Values

Fill values appear in the SMAP Level-1B brightness temperature product in any of the following circumstances:

  • No measured data for the maximum possible number of footprints. The total number of radiometer science packets per antenna scan varies depending on the antenna rotation rate and integration time of the instrument. The resulting number of antenna footprints per scan is therefore variable. To preserve the shape of stored data elements, the size of certain dimensions is assigned a maximum value. Thus, fill values appear in the SMAP Level-1B brightness temperature product when a particular scan does not contain the maximum possible number of footprints.
  • RFI detection algorithms flag all pixels which make up a footprint. High resolution radiometer instrument data contains radiometer counts which are integrated every approximately 300 µs per PRI and every 1 ms per packet. These radiometer counts are calibrated to produce antenna temperatures referenced to the feedhorn. The antenna temperatures are then processed by RFI detection and mitigation algorithms where the pixels for a footprint that are flagged for RFI are removed and the remaining clean pixels are averaged to form an RFI free antenna footprint. If all pixels for a particular footprint are flagged for RFI, then the footprint TA is assigned the null value. The corresponding footprint brightness temperature, brightness temperature value will also be assigned the null value since the RFI-free antenna footprint TAs are used to produce the time-ordered brightness temperature product. Subsequently, after pixels with RFI are flagged and dropped, the remaining clean pixels are used to compute the NEDT for that footprint. If all pixels are removed the null value is assigned to the NEDT for that footprint.
  • The NEDT for the footprint after RFI removal is 0. A single pixel may be left after RFI removal. The product will contain an associated footprint TA and TB value; however the NEDT will be 0. The null value will be assigned to the NEDT value in this case but the corresponding TA and TB values will be reported.

SMAP data products employ a specific set of data values to connote that an element is fill. The selected values that represent fill are dependent on the data type.

No valid value in the Level-1B brightness temperature product is equal to the values that represent fill. If any exceptions should exist in the future, the Level-1B brightness temperature content will provide a means for users to discern between elements that contain fill and elements that contain genuine data values. This document will also contain a description of the method used to ascertain which elements are fill and which elements are genuine. 

The Level-1B brightness temperature product records gaps when entire frames within the time span of a particular data granule do not appear. Gaps can occur under one of two conditions:

  • One or more complete frames of data are missing from all data streams.
  • The subset of input data that is available for a particular frame is not sufficient to process any frame output.

The Level-1B brightness temperature product records gaps in the product-level metadata. The following conditions will indicate that no gaps appear in the data product:

  • Only one instance of the attributes Extent/rangeBeginningDateTime and Extent/rangeEndingDateTime will appear in the product metadata.
  • The character string stored in metadata element Extent/rangeBeginningDateTime will match the character string stored in metadata elementOrbitMeasuredLocation/halfOrbitStartDateTime.
  • The character string stored in metadata element Extent/rangeEndingDateTime will match the character string stored in metadata elementOrbitMeasuredLocation/halfOrbitStopDateTime.

One of two conditions will indicate that gaps appear in the data product:

  • The time period covered between Extent/rangeBeginningDateTime and Extent/RangeEndingDateTime does not cover the entire half orbit as specified inOrbitMeasuredLocation/halfOrbitStartDateTime and OrbitMeasuredLocation/halfOrbitStartDateTime.
  • More than one pair of Extent/rangeBeginningDateTime and Extent/rangeEndingDateTime appears in the data product. Time periods within the time span of the half orbit that do not fall within the sets of Extent/rangeBeginningDateTime and Extent/rangeEndingDateTime constitute data gaps.

Bit flag elements in the Level-1B brightness temperature product often provide additional information about missing data. For example, the data element tb_v in the Level-1B brightness temperature product contains bit flags that indicate the quality of data for each footprint. Each of the tb_qual_flag_v variables indicates the quality of the data in each footprint. When a data frame is deemed unusable, the appropriate bits in the tb_qual_flag_v should indicate the rationale.

If data values associated with any particular look of the radiometer instrument creates untenable algorithmic conditions, the Level-1B brightness temperature Science Production Software (SPS) may curtail processing for that look. When these conditions take place, the Level-1B brightness temperature product displays whatever values the SPS was able to calculate. When a tb_v measure for a particular footprint has been deemed unusable, the appropriate bits in the tb_qual_flag_v will provide users with a rationale for the missing data.

Acronyms and Abbreviations

Table A12 defines the acronyms and abbreviations used in this document.

Table A12. Acronyms and Abbreviations
Abbreviation Definition
ABFCS Antenna Beam Frame Coordinate System
ATBD Algorithm Theoretical Basis Document
Char 8-bit character
Int8 8-bit (1-byte) signed integer
Int16 16-bit (2-byte) signed integer
Int32 32-bit (4-byte) signed integer
ECR Earth Centered Rotating
ET Ephemeris Time
Float32 32-bit (4-byte) floating-point integer
Float64 64-bit (8-byte) floating-point integer
H-pol Horizontally polarized
N/A Not Applicable
NEDT Noise Equivalent Delta Temperature
PRI Pulse Repetition Interval
RFI Radio Frequency Interference
SI International System of Units
SPS Science Production Software
SRF Science Orbit Reference Frame
TA Antenna Temperature
TB Brightness Temperature
Uint8 8-bit (1-byte) unsigned integer
Uint16 16-bit (2-byte) unsigned integer
UTC Universal Coordinated Time
V-pol Vertically polarized

FAQ

What are the latencies for SMAP radiometer data sets?
The following table describes both the required and actual latencies for the different SMAP radiometer data sets. Latency is defined as the time (# days, hh:mm:ss) from data acquisition to product generation. Short name Title Latency Required Actual (mean1) SPL1AP SMAP L1A... read more

How To

How do I visualize SMAP data in Worldview?
This video tutorial provides step-by-step instructions on how to visualize SMAP data in Worldview (http://worldview.earthdata.nasa.gov/). NASA Worldview is a map-based application... read more
How do I search, order, and customize SMAP data using Earthdata Search?
In this step-by-step tutorial, we will demonstrate how to search, order, and customize NASA Soil Moisture Active Passive, or SMAP data using the NASA Earthdata Search application. NASA Earthdata search provides an interactive map-based search environment where you can filter your results based on... read more
Programmatically access data using spatial and temporal filters
This article provides a step-by-step getting started guide to utilizing an Application Programming Interface, or API, for programmatic access to data from the NSIDC Distributed Active Archive Center (DAAC) based on spatial and temporal filters. Programmatic access is provided via an HTTPS URL... read more
How to learn more about SMAP ancillary data
SMAP Ancillary data sets are used to produce SMAP Level-1, -2, -3, and -4 standard data products. Several of these ancillary data sets are produced by external organizations, such as NOAA, the NASA Global Modeling and Assimilation... read more
How to visualize SMAP WMS layers with ArcGIS and Google Earth
NASA's Global Imagery Browse Services (GIBS) provides up to date, full resolution imagery for selected SMAP data sets. Adding GIBS layers via OGC methods, such as Web Map Service (WMS), Web Map Tile Service (WMTS) and Tiled Web Map Service (TWMS) provides an easy way to visualize the entire time... read more