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

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 birghtness 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_row Uint16 2 0 405 (M36)
499 (N36/S36)
N/A -9999.0 2
cell_col Uint16 2 0 963 (M36)
499 (N36/S36)
N/A N/A 2
cell_center_lat Float32 4 -90.0 +90.0 Degree 65534 2
cell_center_lon Float32 4 -180.0 +180.0 Degree 65534 2
Fore-
Looking
Data Arrays
cell_tb_time_seconds_fore Float64 8 0 N/A Second 65534 1
cell_tb_time_utc_fore Char24 24 2014-10-31
T00:00:00.000Z
N/A N/A 1
cell_centroid_lat_fore Float32 4 -90.0 +90.0 Degree 65534 1
cell_centroid_lon_fore Float32 4 -180.0 +180.0 Degree 65534 1
cell_antenna_scan_angle_fore Float32 4 -180.0 +180.0 Degree 65534 1
cell_boresight_incidence_fore Float32 4 0 90.0 Degree 65534 1
cell_solar_specular_theta_fore Float32 4 0 90.0 Degree 65534 1
cell_solar_specular_phi_fore Float32 4 0 360.0 Degree 65534 1
cell_tb_h_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_v_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_3_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_4_fore Float32 4 0 340.0 Kelvin 65534 1
cell_number_measurements_h_fore Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_v_fore Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_3_fore Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_4_fore Uint16 2 1 N/A N/A -9999.0 1
cell_tb_error_h_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_v_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_3_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_4_fore Float32 4 0 340.0 Kelvin 65534 1
cell_tb_qual_flag_h_fore Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_v_fore Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_3_fore Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_4_fore Uint16 2 0 65,536 N/A -9999.0 1
Aft-
Looking
Data Arrays
cell_tb_time_seconds_aft Float64 8 0 N/A Second 65534 1
cell_tb_time_utc_aft Char24 24 2014-10-31T00:00:00.000Z N/A N/A 1
cell_centroid_lat_aft Float32 4 -90.0 +90.0 Degree 65534 1
cell_centroid_lon_aft Float32 4 -180.0 +180.0 Degree 65534 1
cell_antenna_scan_angle_aft Float32 4 -180.0 +180.0 Degree 65534 1
cell_boresight_incidence_aft Float32 4 0 90.0 Degree 65534 1
cell_solar_specular_theta_aft Float32 4 0 90.0 Degree 65534 1
cell_solar_specular_phi_aft Float32 4 0 360.0 Degree 65534 1
cell_tb_h_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_v_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_3_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_4_aft Float32 4 0 340.0 Kelvin 65534 1
cell_number_measurements_h_aft Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_v_aft Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_3_aft Uint16 2 1 N/A N/A -9999.0 1
cell_number_measurements_4_aft Uint16 2 1 N/A N/A -9999.0 1
cell_tb_error_h_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_v_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_3_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_error_4_aft Float32 4 0 340.0 Kelvin 65534 1
cell_tb_qual_flag_h_aft Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_v_aft Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_3_aft Uint16 2 0 65,536 N/A -9999.0 1
cell_tb_qual_flag_4_aft Uint16 2 0 65,536 N/A -9999.0 1

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_row

Row index of a 36 km EASE-Grid 2.0 cell.

cell_col

Column index of a 36 km EASE-Grid 2.0 cell.

cell_center_lat

Latitude of the center of a 36 km EASE-Grid 2.0 cell.

cell_center_lon

Longitude of the center of a 36 km EASE-Grid 2.0 cell.

cell_tb_time_seconds_[ fore | aft ]

Weighted average of UTC acquisition times of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell. The result is then expressed in J2000 seconds (the number of seconds since 11:58:55.816 UTC on 01 January 2000.

cell_tb_time_utc_[ fore | aft ]

ASCII representation of the weighted average of UTC acquisition times of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_centroid_lat_[ fore | aft ]

Weighted average of latitudes of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_centroid_lon_[ fore | aft ]

Weighted average of longitudes of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_antenna_scan_angle_[ fore | aft ]

Weighted average of antenna scan angles of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell. The antenna scan angle is defined as the azimuth angle of the antenna measured from the ground track vector. The azimuth angle is 0° when the antenna points in the same direction as the ground track vector and increases clockwise (i.e., towards +180°) when viewed from above.

cell_boresight_incidence_[ fore | aft ]

Weighted average of incidence angles of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell. The incidence angle is defined as the included angle between the antenna boresight vector and the normal to the Earth’s surface.

cell_solar_specular_theta_[ fore | aft ]

Weighted average of the elevation component of solar specular angles of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_solar_specular_phi_[ fore | aft ]

Weighted average of the azimuth component of solar specular angles of the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_h_[ fore | aft ]

Weighted average of Level-1B horizontally polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_v_[ fore | aft ]

Weighted average of Level-1B vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_3_[ fore | aft ]

Weighted average of Level-1B 3rd Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_4_[ fore | aft ]

Weighted average of Level-1B 4th Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_number_measurements_h_[ fore | aft ]

Number of Level-1B horizontally polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_number_measurements_v_[ fore | aft ]

Number of Level-1B vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_number_measurements_3_[ fore | aft ]

Number of Level-1B 3rd Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_number_measurements_4_[ fore | aft ]

Number of Level-1B 4th Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_error_h_[ fore | aft ]

Weighted average of the errors of Level-1B horizontally polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_error_v_[ fore | aft ]

Weighted average of the errors of Level-1B vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_error_3_[ fore | aft ]

Weighted average of the errors of Level-1B 3rd Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_error_4_[ fore | aft ]

Weighted average of the errors of Level-1B 4th Stokes parameters whose boresights fall within a 36 km EASE-Grid 2.0 cell.

cell_tb_qual_flag_h_[ fore | aft ]

A 16-bit or two-byte binary number indicating the quality of individual the Level-1B brightness temperature observations used to derive the the Level-1C brightness temperature data. Among those the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell, a 0 indicates that all the Level-1B brightness temperature observations satisfy a given quality criterion described in the Level-1B brightness temperature’s tb_qual_flag_h output parameter; a 1 indicates that the same criterion is violated by at least one the Level-1B brightness temperature observation. Bit position 0 refers to the least-significant digit. See Table 2.

cell_tb_qual_flag_v_[ fore | aft ]

A 16-bit or two-byte binary number indicating the quality of individual the Level-1B brightness temperature observations used to derive the Level-1C brightness temperature data. Among those the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell, a 0 indicates that all the Level-1B brightness temperature observations satisfy a given quality criterion described in the Level-1B brightness temperature's tb_qual_flag_v output parameter; a 1 indicates that the same criterion is violated by at least one the Level-1B brightness temperature observation. Bit position 0 refers to the least significant digit. See Table 2.

cell_tb_qual_flag_3_[ fore | aft ]

A 16-bit or two-byte binary number indicating the quality of individual the Level-1B brightness temperature observations used to derive the Level-1C brightness temperature data. Among those the Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell, a 0 indicates that all the Level-1B brightness temperature observations satisfy a given quality criterion described in the Level-1B brightness temperature's tb_qual_flag_3 output parameter; a 1 indicates that the same criterion is violated by at least one the Level-1B brightness temperature observation. Bit position 0 refers to the least significant digit. See Table 2.

cell_tb_qual_flag_4_[ fore | aft ]

A 16-bit or two-byte binary number indicating the quality of individual the Level-1B brightness temperature observations used to derive the Level-1C brightness temperature data. Among those Level-1B brightness temperature observations whose boresights fall within a 36 km EASE-Grid 2.0 cell, a 0 indicates that all the Level-1B brightness temperature observations satisfy a given quality criterion described in the Level-1B brightness temperature's tb_qual_flag_4 output parameter; a 1 indicates that the same criterion is violated by at least one the Level-1B brightness temperature observation. Bit position 0 refers to the least significant digit. See Table 2.

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