Data Fields - SMAP L1C Radiometer Half-Orbit 36 km EASE-Grid Brightness Temperatures, Version 4

This page provides a description of all data fields within the SMAP L1C Radiometer Half-Orbit 36 km EASE-Grid Brightness Temperatures (SPL1CTB) product. The data are grouped in the following main HDF5 groups:

For a description of metadata fields for this product, refer to the Metadata Fields document.

North, South, and Global Projections

Tables 1 describes the data fields within the HDF5 group for each projection. Data are provided in three EASE-Grid 2.0 projections:

  • Global (M36, or Midlatitude 36 km)
  • North (N36, or North 36 km)
  • South (S36, or South 36 km)

Within each group, the data are provided in fore-looking and aft-looking views. Data from the fore- and aft-look portions of the 360° antenna scan are provided separately in order to benefit radiometric analyses over regions where there is strong brightness temperature (TB) azimuthal dependence. Each set of looks contains brightness temperature observations, instrument viewing geometry information, and quality bit flags. The fore-looking set refers to information derived from the Level-1B brightness temperature observations acquired in the forward-looking portion of the scans when the antenna angle falls between -90 degrees and 90 degrees; the aft-looking set refers to information derived from the Level-1B brightness temperature observations acquired in the backward-looking portion of the scans. Only those cells that are covered by the swath for a given projection are written in the product.

Table 1. Data Fields for North_Polar_Projection, South_Polar_Projection, and Global_Projection
Azimuth
Direction
Data Field Name Type Byte Valid Min Valid Max Unit Fill/Gap Value Derivation Method*
N/A cell_column Uint16 2 0 963  N/A 65534 2
cell_grid_surface_status Uint16 2 0 1 N/A 65534 2
cell_lat Float32 4 -90.0 90.0 Degree 65534 2
cell_lon Float32 4 -180.0 180.0 Degree 65534 2
cell_row Uint16 2 0 405  N/A -9999.0 2
Fore-
Looking
Data Arrays
cell_antenna_scan_angle_fore Float32 4 0.0 359.999 Degree -9999.0 1
cell_boresight_incidence_fore Float32 4 0.0 180.0 Degree -9999.0 1
cell_centroid_lat_fore Float32 4 -90.0 90.0 Degree -9999.0 1
cell_centroid_lon_fore Float32 4 -180.0 180.0 Degree -9999.0 1
cell_number_measurements_3_fore Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_4_fore Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_h_fore Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_v_fore Uint16 2 0 65535 N/A 65534 1
cell_solar_specular_phi_fore Float32 4 0.0 359.999 Degree 65534 1
cell_solar_specular_theta_fore Float32 4 0.0 90.0 Degree -9999.0 1
cell_surface_water_fraction_mb_h_fore Float32 4 0.0 1.0 N/A -9999.0 1
cell_surface_water_fraction_mb_v_fore Float32 4 0.0 1.0 N/A -9999.0 1
cell_tb_3_fore Float32 4 -50.0 50.0 Kelvin -9999.0 1
cell_tb_4_fore Float32 4 -50.0 50.0 Kelvin -9999.0 1
cell_tb_error_3_fore Float32 4 -50.0 50.0 Kelvin -9999.0 1
cell_tb_error_4_fore Float32 4 -50.0 50.0 Kelvin -9999.0 1
cell_tb_error_h_fore Float32 4 0.0 330.0 Kelvin -9999.0 1
cell_tb_error_v_fore Float32 4 0.0 330.0 Kelvin -9999.0 1
cell_tb_h_surface_corrected_fore Float32 4 0.0 330.0 Kelvin -9999.0 1
cell_tb_qual_flag_3_fore Uint16 2 0 65,536 N/A 65534 1
cell_tb_qual_flag_4_fore Uint16 2 0 65,536 N/A 65534 1
cell_tb_qual_flag_h_fore Uint16 2 0 65,536 N/A 65534 1
cell_tb_qual_flag_v_fore Uint16 2 0 65,536 N/A 65534 1
cell_tb_time_seconds_fore Uint16 2 -999999.9 9.4E8 Seconds -9999.0 1
cell_tb_time_utc_fore String 24 2014-10-31
T00:00:00.000Z
N/A N/A N/A 1
cell_tb_v_fore Float32 4 0.0 330.0 Kelvin -9999.0 1
cell_tb_v_surface_corrected_fore Float32 4 0.0 330.0 Kelvin -9999.0 1
Aft-
Looking
Data Arrays
cell_antenna_scan_angle_aft Float32 4 0.0 359.999 Degree -9999.0 1
cell_boresight_incidence_aft Float32 4 0.0 180.0 Degree -9999.0 1
cell_centroid_lat_aft Float32 4 -90.0 90.0 Degree -9999.0 1
cell_centroid_lon_aft Float32 4 -180.0 179.999 Degree -9999.0 1
cell_number_measurements_3_aft Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_4_aft Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_h_aft Uint16 2 0 65535 N/A 65534 1
cell_number_measurements_v_aft Uint16 2 0 65535 N/A 65534 1
cell_solar_specular_phi_aft Float32 4 0.0 359.999 Degree -9999.0 1
cell_solar_specular_theta_aft Float32 4 0.0 90.0 Degree -9999.0
cell_surface_water_fraction_mb_h_aft Float32 4 0.0 1.0 N/A -9999.0
cell_surface_water_fraction_mb_v_aft Float32 4 0.0 1.0 N/A -9999.0
cell_tb_3_aft Float32 4 -50.0 50.0 Kelvin -9999.0
cell_tb_4_aft Float32 4 -50.0 50.0 Kelvin -9999.0
cell_tb_error_3_aft Float32 4 -50.0 50.0 Kelvin -9999.0
cell_tb_error_4_aft Float32 4 -50.0 50.0 Kelvin -9999.0
cell_tb_error_h_aft Float32 4 0.0 330.0 Kelvin -9999.0
cell_tb_error_v_aft Float32 4 0.0 330.0 Kelvin -9999.0
cell_tb_h_surface_corrected_aft Float32 4 0.0 330.0 Kelvin -9999.0
cell_tb_qual_flag_3_aft Uint16 2 0 65,536 N/A -9999.0
cell_tb_qual_flag_4_aft Uint16 2 0 65,536 N/A -9999.0
cell_tb_qual_flag_h_aft Uint16 2 0 65,536 N/A -9999.0
cell_tb_qual_flag_v_aft Uint16 2 0 65,536 N/A -9999.0
cell_tb_time_seconds_aft Float64 4 -999999.9 9.4E8 Seconds -9999.0
cell_tb_time_utc_aft Uint16 2 ?? ?? ?? -9999.0 1
cell_tb_v_aft Float32 4 0.0 330.0 Kelvin -9999.0
cell_tb_v_surface_corrected_aft Float32 4 0.0 330.0 Kelvin -9999.0

Derivation methods are:

  1. From Level-1C brightness temperature data
  2. From 36 km EASE-Grid 2.0 array definition
  3. Value corrected for the presence of water wherever water/land areal fraction is below a threshold; when the fraction is zero, no correction is performed.
  4. Determined by Level-2 soil moisture passive processing software
  5. Available only with option algorithms that use two polarization channels
  6. From external ancillary data whose location and timestamp coincide with those of the input data
  7. From Level-2 soil moisture active data

Metadata [top]

For a description of all metadata fields for this product, refer to the Metadata Fields document.

Data Field Definitions [top]

All data field definitions below are valid for fore-looking and aft-looking groups, as well as ascending and descending half-orbit files.

cell_column 
EASE grid column index of cell on world grid in longitude direction.

cell_grid_surface_status
Indicates if the grid point lies on land (0) or water (1).

cell_lat

Latitude of the center of the Earth-based grid cell.

cell_lon

Longitude of the center of the Earth-based grid cell.

cell_row

EASE grid row index of cell on world grid in latitude direction.

cell_antenna_scan_angle fore|aft

Representative scan angle of the SMAP antenna on the spacecraft for all forward-looking footprints within the cell.

cell_boresight_incidence fore|aft

Representative angle between the antenna boresight vector and the normal to the Earth's surface for all forward-looking footprints within the cell. Representative scan angle of the SMAP antenna on the spacecraft for all aft-looking footprints within the cell.

cell_lat_centroid fore|aft

Weighted average of the latitude of the center of the forward-looking brightness temperature footprints that fall within the EASE-Grid cell. Representative angle between the antenna boresight vector and the normal to the Earth's surface for all aft-looking footprints within the cell.

cell_lon_centroid fore|aft

Weighted average of the longitude of the center of the forward-looking brightness temperature footprints that fall within the EASE-Grid cell. Weighted average of the latitude of the center of the aft-looking brightness temperature footprints that fall within the EASE-Grid cell.

cell_number_measurements_3 fore|aft
Number of forward-looking TB3 samples within the grid cell that were used to calculate the representative value in this product. Weighted average of the longitude of the center of the aft-looking brightness temperature footprints that fall within the EASE-Grid cell. Number of aft-looking TB3 samples within the grid cell that were used to calculate the representative value in this product.

cell_number_measurements_4 fore|aft
Number of forward-looking TB4 samples within the grid cell that were used to calculate the representative value in this product. Number of aft-looking TB4 samples within the grid cell that were used to calculate the representative value in this product.

cell_number_measurements_h fore|aft
Number of forward-looking TBH samples within grid cell that were used to calculate the representative value in this product. Number of aft-looking TBH samples within grid cell that were used to calculate the representative value in this product.

cell_number_measurements_v fore|aft
Number of forward-looking TBV samples within grid cell that were used to calculate the representative value in this product. Number of aft-looking TBV samples within grid cell that were used to calculate the representative value in this product.

cell_solar_specular_phi fore|aft
Weighted average of the azimuthal component of a spatial angle defined by the vector that extends from the sun to the solar glint spot and the antenna boresight vector for forward-looking footprints within the cell. Weighted average of the azimuthal component of a spatial angle defined by the vector that extends from the sun to the solar glint spot and the antenna boresight vector for aft-looking footprints within the cell.

cell_solar_specular_theta fore|aft 
Weighted average of the elevation component of the spatial angle defined by the vector that extends from the sun to the solar glint spot and the antenna boresight vector for forward-looking footprints within the cell. Weighted average of the elevation component of the spatial angle defined by the vector that extends from the sun to the solar glint spot and the antenna boresight vector for aft-looking footprints within the cell.

cell_surface_water_fraction_mb_h fore|aft
Gain-weighted fraction of static water within the forward-looking horizontally polarized antenna pattern. Gain-weighted fraction of static water within the aft-looking horizontally polarized antenna pattern.

cell_surface_water_fraction_mb_v fore|aft
Gain-weighted fraction of static water within the forward-looking vertically polarized antenna pattern. Gain-weighted fraction of static water within the aft-looking vertically polarized antenna pattern.

cell_tb_3 fore|aft
Representative TB3 for all forward-looking samples that fall within the grid cell. Representative TB3 for all aft-looking samples that fall within the grid cell.

cell_tb_4 fore|aft
Representative TB4 for all forward-looking samples that fall within the grid cell. Representative TB4 for all aft-looking samples that fall within the grid cell.

cell_tb_error_3 fore|aft
Error measure of the representative TB3 for all forward-looking samples that fall within the grid cell. Error measure of the representative TB3 for all aft-looking samples that fall within the grid cell.

cell_tb_error_4 fore|aft
Error measure of the representative TB4 for all forward-looking samples that fall within the grid cell. Error measure of the representative TB4 for all aft-looking samples that fall within the grid cell.

cell_tb_error_h fore|aft
Error measure of the representative TBH for all forward-looking samples that fall within the grid cell. Error measure of the representative TBH for all aft-looking samples that fall within the grid cell. 

cell_tb_error_v fore|aft
Error measure of the representative TBV for all forward-looking samples that fall within the grid cell. Error measure of the representative TBV for all aft-looking samples that fall within the grid cell.

cell_tb_h fore|aft
Representative TBH for all forward-looking samples that fall within the grid cell. Representative TBH for all aft-looking samples that fall within the grid cell.

cell_tb_h_surface_corrected fore|aft
Water/land contamination corrected forward-looking horizontally polarized brightness temperature at the surface after RFI filtering within the grid cell. Water/land contamination corrected aft-looking horizontally polarized brightness temperature at the surface after RFI filtering within the grid cell.

cell_tb_qual_flag_3 fore|aft
Bit flags that represent the quality of the forward looking 3rd Stokes brightness temperature each grid cell. Bit flags that represent the quality of the aft looking 3rd Stokes brightness temperature each grid cell.

cell_tb_qual_flag_4 fore|aft
Bit flags that represent the quality of the forward looking 4th Stokes brightness temperature each grid cell. Bit flags that represent the quality of the aft looking 4th Stokes brightness temperature each grid cell.

cell_tb_qual_flag_h fore|aft
Bit flags that represent the quality of the forward looking horizontal polarization brightness temperature within each grid cell. Bit flags that represent the quality of the aft looking horizontal polarization brightness temperature within each grid cell.

cell_tb_qual_flag_v fore|aft
Bit flags that represent the quality of the forward looking vertical polarization brightness temperature within each grid cell. Bit flags that represent the quality of the aft looking vertical polarization brightness temperature within each grid cell.

cell_tb_time_seconds fore|aft
Weighted average of the acquisition time of all of the forward-looking brightness temperature footprints with a center that falls within the EASE-Grid cell in seconds since noon on January 1, 2000 UTC. Weighted average of the acquisition time of all of the aft-looking brightness temperature footprints with a center that falls within the EASE-Grid cell in seconds since noon on January 1, 2000 UTC.

cell_tb_time_utc fore|aft
ASCII representation of the weighted average of the acquisition time of all of the forward-looking brightness temperature footprints with a center that falls within the EASE-Grid cell in UTC. ASCII representation of the weighted average of the acquisition time of all of the aft-looking brightness temperature footprints with a center that falls within the EASE-Grid cell in UTC.

cell_tb_v fore|aft
Representative TBV for all forward-looking samples that fall within the grid cell. Representative TBV for all aft-looking samples that fall within the grid cell.

cell_tb_v_surface_corrected fore|aft
Water/land contamination corrected forward- and aft-looking vertically polarized brightness temperature at the surface after RFI filtering within the grid cell. Water/land contamination corrected aft-looking vertically polarized brightness temperature at the surface after RFI filtering within the grid cell.

Table 2. Bit Values for all Cell TB Quality Flags (TH, TV, T3, and T4)
Bit Position Bit Value and Interpretation
0 0 = Has acceptable quality
1 = Does not have acceptable quality
1 0 = Within expected range
1 = Beyond expected range
2 0 = RFI not detected
1 = RFI detected
3 0 = RFI detected and corrected (RFI algorithm functioned correctly; however, does not indicate that resultant bit is RFI free)
1 = RFI was detected but not correctable in the observation
4 0 = Has acceptable NEDT
1 = Has unacceptable NEDT
5 0 = Solar direct TB correction successful
1 = Solar direct TB correction not successful
6 0 = Solar specular TB correction successful
1 = Solar specular TB correction not successful
7 0 = Lunar specular TB correction successful
1 = Lunar specular TB correction not successful
8 0 = Galactic specular TB correction successful
1 = Galactic specular TB correction not successful
9 0 = Atmospheric correction successful
1 = Atmospheric correction not successful
10 0 = Faraday rotation correction successful
1 = Faraday rotation correction not successful
11 0 = Faraday rotation correction was successful
1 = Faraday rotation correction was not successful
12 0 = The corresponding brightness temperature element contains a calculated value
1 = The corresponding brightness temperature element is null
13 0 = Observation was within half orbit
1 = Observation was outside half orbit
14 0 = The difference between TA filtered and TA is less than the threshold
1 = The difference between TA filtered and TA is not less than the threshold
15

0 = Radiometer processor declares a pixel is free of RFI by incorporating the following factors:

  • The data are in range (Bit 1)
  • The RFI removal algorithm worked (Bit 3)
  • The data do not display high NEDT (Bit 4)
  • The difference between TA filtered and TA is less than a specific threshold (Bit 14)
1 = Radiometer processor does not declare a pixel is free of RFI

Fill/Gap Values [top]

SMAP data products employ fill and gap values to indicate when no valid data appear in a particular data element. Fill values ensure that data elements retain the correct shape. Gap values locate portions of a data stream that do not appear in the output data file.

Fill values appear in the SMAP Level-1C brightness temperature product when the Level-1C brightness temperature Science Production Software (SPS) can process some, but not all, of the input data for a particular swath grid cell. Fill data may appear in the product in any of the following circumstances:

  • One of SPS executables that generate the SMAP Level-1C brightness temperature product is unable to calculate a particular science or engineering data value. The algorithm encounters an error. The error disables generation of valid output. The SPS reports a fill value instead.
  • Some of the required science or engineering algorithmic input are missing. Data over the region that contributes to particular grid cell may appear in only some of the input data streams. Since data are valuable, the Level-1C brightness temperature product records any outcome that can be calculated with the available input. Missing data appear as fill values.
  • Non-essential information is missing from the input data stream. The lack of non-essential information does not impair the algorithm from generating needed output. The missing data appear as fill values.
  • Fill values appear in the input radiometer the Level-1B brightness temperature product. If only some of the input that contributes to a particular grid cell is fill data, the Level-1C brightness temperature SPS will most likely be able to generate some output. However, some portion of the Level-1C brightness temperature output for that grid cell may appear as fill values.

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-1C brightness temperature product is equal to the values that represent fill. If any exceptions should exist in the future, the Level-1C 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-1C 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-1C 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.

Acronyms and Abbreviations [top]

Table 3 defines the acronyms and abbreviations used in this document.

Table 3. Acronyms and Abbreviations
Abbreviation Definition
ABFCS Antenna Beam Frame Coordinate System
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