Data Fields - SMAP Enhanced L2 Radiometer Half-Orbit 9 km EASE-Grid Soil Moisture, Version 2

 This page provides a description of all data fields within the SMAP Enhanced L2 Radiometer Half-Orbit 9 km EASE-Grid Soil Moisture (SPL2SMP_E) product. The data are grouped into two main HDF5 groups:

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

Soil_Moisture_Retrieval_Data

Table 1 describes the data fields of a typical half-orbit granule for this product. All data element arrays are one-dimensional with a size N, where N is the number of valid cells from the radiometer swath that appear on the grid.

Table 1. Data Fields for Soil_Moisture_Retrieval_Data
Data Field Name Type Byte Unit Valid Min Valid Max Fill/Gap Value Dimensions
(Number of grid cells covered by swath)
Derivation Method(s)*
EASE_column_index Uint16 2 N/A 0 1623 65534 N 2
EASE_row_index Uint16 2 N/A 0 3855 65534 N 2
albedo Float32 4 N/A 0.0 1.0 -9999.0 N 6
boresight_incidence Float32 4 Degree 0.0 90.0 -9999.0 N 1
freeze_thaw_fraction Float32 4 N/A 0.0 1.0 -9999.0 N 6
grid_surface_status Uint16 2 N/A 0 1 65534 N 6
latitude Float32 4 Degree -90.0 +90.0 -9999.0 N 2
latitude_centroid Float32 4 Degree -90.0 90.0 -9999.0 N 1
longitude Float32 4 Degree -180.0 +180.0 -9999.0 N 2
longitude_centroid Float32 4 Degree -180.0 179.999 -9999.0 N 1
radar_water_body_fraction Float32 4 N/A 0.0 1.0 -9999.0 N 6
retrieval_qual_flag Uint16 2 N/A 0 65,536 65534 N 4
retrieval_qual_flag_option1 Uint16 2 N/A 0 65,536 65534 N 4
retrieval_qual_flag_option2 Uint16 2 N/A 0 65,536 65534 N 4
retrieval_qual_flag_option3 Uint16 2 N/A 0 65,536 65534 N 4
retrieval_qual_flag_option4 Uint16 2 N/A 0 65,536 65534 N 4
retrieval_qual_flag_option5 Uint16 2 N/A 0 65,536 65534 N 4
roughness_coefficient Float32 4 N/A 0.0 1.0 -9999.0 N 6
soil_moisture Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
soil_moisture_error Float32 4 cm3/cm3 0.0 0.2 -9999.0 N 4 or 6
soil_moisture_option1 Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
soil_moisture_option2 Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
soil_moisture_option3 Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
soil_moisture_option4 Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
soil_moisture_option5 Float32 4 cm3/cm3 0.02 0.5 -9999.0 N 4
static_water_body_fraction Float32 4 N/A 0.0 1.0 -9999.0 N 6
surface_flag Uint16 2 N/A 0 65,536 65534 N 4
surface_temperature Float32 4 Kelvin 0.0 350.0 -9999.0 N 6
surface_water_fraction_mb_h Float32 4 Kelvin 0.0 1.0 -9999.0 N 6
surface_water_fraction_mb_v Float32 4 Kelvin 0.0 1.0 -9999.0 N 6
tb_3_corrected Float32 4 Kelvin -50.0 50.0 -9999.0 N 3
tb_4_corrected3 Float32 4 Kelvin -50.0 50.0 -9999.0 N 3
tb_h_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 N 3
tb_h_uncorrected Float32 4 Kelvin 0.0 330.0 -9999.0 N 1
tb_qual_flag_3 Uint16 2 N/A 0 65,536 65534 N 4
tb_qual_flag_4 Uint16 2 N/A 0 65,536 65534 N 4
tb_qual_flag_h Uint16 2 N/A 0 65,536 65534 N 4
tb_qual_flag_v Uint16 2 N/A 0 65,536 65534 N 4
tb_time_seconds Float64 8 Second -999999.9 9.4E8 -9999.0 N 1
tb_time_utc Char24 24 N/A 2014-10-31T
00:00:00.000Z
N/A 16777214 N 1
tb_v_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 N 3
tb_v_uncorrected Float32 4 Kelvin 0.0 330.0 -9999.0 N 1
vegetation_opacity Float32 4 N/A 0.0 10.0 -9999.0 N 6
vegetation_opacity_option1 Float32 4 N/A 0.01 10.00 -9999.0 N 6
vegetation_opacity_option2 Float32 4 N/A 0.01 10.00 -9999.0 N 6
vegetation_opacity_option3 Float32 4 N/A 0.01 10.00 -9999.0 N 5
vegetation_opacity_option4 Float32 4 N/A 0.01 10.00 -9999.0 N 5
vegetation_opacity_option5 Float32 4 N/A 0.01 10.00 -9999.0 N 5
vegetation_water_content Float32 4 kg/m2 0 20.0 -9999.0 N 6

* 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 radiometer soil moisture 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

Data Field Definitions [top]

EASE_column_index

The column index of the 9 km EASE grid cell that contains the associated data.

EASE_row_index

The row index of the 9 km EASE grid cell that contains the associated data.

albedo

Diffuse reflecting power of the Earth's surface within the grid cell.

boresight_incidence

Representative angle between the antenna boresight vector and the normal to the Earth's surface for all footprints within the cell.

freeze_thaw_fraction

Fraction of the 9 km grid cell that is denoted as frozen.  Based on binary flag that specifies freeze thaw conditions in each of the component 3 km grid cells.

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

latitude

Latitude of the center of the Earth based grid cell.

latitude_centroid

Weighted average of the latitude of the center of the  brightness temperature footprints that fall within the EASE grid cell.

longitude

Longitude of the center of the Earth based grid cell.

longitude_centroid

Weighted average of the longitude of the center of the brightness temperature footprints that fall within the EASE grid cell.

radar_water_body_fraction

The fraction of the area of the 9 km grid cell that is covered by water based on the radar detection algorithm.

retrieval_qual_flag, retrieval_qual_flag_option[1-5]

Bit flags that record the conditions and the quality of the retrieval algorithms that generate soil moisture within each grid cell. When retrieval is performed, it contains additional bits to further indicate the exit status and quality of the retrieval. A summary of bit definition of the retrieval_qual_flag field is listed below in Table 2. 

The retrieval_qual_flag field is internally linked to the retrieval_qual_flag_option2 field produced by the baseline algorithm. All soil moisture algorithm options, soil moisture data fields, and corresponding retrieval quality flags are listed in Table 4.

Table 2. Retrieval Quality Flag Definition
Bit Retrieval Information Bit Value and Interpretation
0 Recommended Quality 0: Soil moisture retrieval has recommended quality
1: Soil moisture retrieval has uncertain quality
1 Retrieval Attempted 0: Soil moisture retrieval was attempted
1: Soil moisture retrieval was skipped
2 Retrieval Successful 0: Soil moisture retrieval was successful
1: Soil moisture retrieval was not successful
3* Retrieval Successful 0: Freeze/thaw state retrieval was successful
1: Freeze/thaw state retrieval was not successful
4-15 Undefined 0 (not used)
* Flag is set based on value of bit 8 of surface_flag (GMAO Tsurf)

roughness_coefficient

A unitless value that is indicative of bare soil roughness within the 9 km grid cell.

soil_moisture
Representative soil moisture measurement for the Earth based grid cell.

soil_moisture_error

Net uncertainty measure of soil moisture measure for the Earth based grid cell. - Calculation method is TBD.

soil_moisture, soil_moisture_option[1-5]

Representative soil moisture measurement for the Earth based grid cell. At present, the operational SPL2SMP Science Production Software (SPS) produces and stores soil moisture retrieval results from the five algorithms listed in Table 3; retrieval quality flags that correspond to each of these algorithms are also listed in Table 3.

Table 3. Soil Moisture Algorithm Options and Corresponding Data Fields
Algorithm Option Corresponding Data Field Corresponding Retrieval Quality Flag Data Field
Single Channel Algorithm H-pol (SCA-H) soil_moisture_option1 retrieval_qual_flag_option1
Single Channel Algorithm V-pol (SCA-V) – Current Baseline soil_moisture_option2 (Internally linked to the soil_moisture field) retrieval_qual_flag_option2 (Internally linked to the retrieval_qual_flag field)
Dual Channel Algorithm (DCA) soil_moisture_option3 retrieval_qual_flag_option3
Microwave Polarization Ratio Algorithm (MPRA) soil_moisture_option4 retrieval_qual_flag_option4
Extended Dual Channel Algorithm (E-DCA) soil_moisture_option5 retrieval_qual_flag_option5

static_water_body_fraction

The fraction of the area of the 9 km grid cell that is covered by static water based on a Digital Elevation Map.

surface_flag

Bit flags that record ambient surface conditions within each grid cell. The surface_flag field is internally linked to the surface_flag_option1 field produced by the baseline algorithm. Table 4 lists surface condition bit flag definitions.

Note: Bit position '0' refers to the least-significant bit. Final bit positions and definitions are subject to future revision and expansion as needed.

Table 4. Surface Condition Bit Flag Definition
Bit Surface Condition T1 T2 Bit Value and Interpretation
0 Static water 0.05 0.10 0: Water fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
1 Radar-derived Water Fraction 0.05 0.10 0: Water fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
2 Coastal Proximity N/A 1.0 0: Distance to nearby significant water bodies greater than T2 (number of 36-km grid cells):
  • Greater than T2: Retrieval attempted and flagged for recommended quality
  • Less than T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
3 Urban Area 0.50 1.00 0: Urban fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
4 Precipitation 0.05 0.10 0: Precipitation fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
5 Snow 0.05 0.10 0: Snow fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
6 Permanent Ice 0.05 0.10 0: Ice fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
7

Frozen Ground* (from SMAP radiometer-derived F/T state)

0.00 0.90 0: Freeze/thaw fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
8

Frozen Ground (from GMAO Tsurf model)

 

0.00 0.90 0: Freeze/thaw fraction less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
9 Mountainous Terrain 0: Slope standard deviation less than T2:
  • Less than T1: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
10 Dense Vegetation 5.0 30.0 0: Vegetation Water Content (VWC) less than T2:
  • Less than T1 kg/m2: Retrieval attempted and flagged for recommended quality
  • Between T1 and T2: Retrieval attempted and flagged for uncertain quality
1: Otherwise:
  • Above T2: Retrieval skipped
11 Nadir Region N/A N/A 0 (not used in SPL2SMP)
12-15 Undefined 0 (not used in SPL2SMP)

surface_temperature

Temperature at land surface based on GMAO GEOS-5 data.

surface_water_fraction_mb_h
Gain weighted fraction of static water within the radiometer horizontal polarization brightness temperature antenna pattern in 36 km Earth grid cell.

surface_water_fraction_mb_v
Gain weighted fraction of static water within the radiometer vertical polarization brightness temperature antenna pattern in 36 km Earth grid cell.

tb_3_corrected

Third stokes parameter for each 9 km grid cell calculated with an adjustment for the presence of water bodies.

tb_4_corrected

Fourth stokes parameter for each 9 km grid cell calculated with an adjustment for the presence of water bodies.

tb_h_corrected

Horizontal polarization brightness temperature in 9 km Earth grid cell adjusted for the presence of water bodies.

tb_h_uncorrected
Horizontal polarization brightness temperature in 36 km Earth grid cell before adjustment for the presence of water bodies.

tb_qual_flag_3

Bit flags that represent the quality of the 3rd Stokes brightness temperature within each grid cell.

tb_qual_flag_4

Bit flags that represent the quality of the 4th Stokes brightness temperature within each grid cell.

tb_qual_flag_h

Bit flags that represent the quality of the horizontal polarization brightness temperature within each grid cell.

tb_qual_flag_v

Bit flags that represent the quality of the vertical polarization brightness temperature within each grid cell.

tb_time_seconds

Arithmetic average of the acquisition time of all of the brightness temperature footprints with a center that falls within the EASE grid cell in seconds since noon on January 1, 2000 UTC.

tb_time_utc

Arithmetic average of the acquisition time of all of the brightness temperature footprints with a center that falls within the EASE grid cell in UTC.

tb_v_corrected

Vertical polarization brightness temperature in 9 km Earth grid cell adjusted for the presence of water bodies.

tb_v_uncorrected
Vertical polarization brightness temperature in 36 km Earth grid cell before adjustment for the presence of water bodies.

vegetation_opacity, vegetation_opacity_option[1-5]

Estimated vegetation opacity at 36 km spatial scale, as returned by the SPL2SMP processing software when the Dual Channel Algorithm (DCA) is used. Note that this parameter is the same 'tau' parameter normalized by the cosine of the incidence angle in the 'tau-omega' model, where:

tau-omega equation

The valid minimum and maximum are subject to further analysis on real data. The vegetation_opacity field is internally linked to the vegetation_opacity_option2 field produced by the baseline algorithm. The measured opacity of the vegetation in the grid cell.

vegetation_water_content

Representative measure of water in the vegetation within the 9 km grid cell.

Metadata [top]

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

Fill/Gap Values [top]

SMAP data products employ fill 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 SPL2SMP product when the SPL2SMP 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 SPL2SMP 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 SPL2SMP 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 Level-1C brightness temperature product.

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. Table 1 lists the values that represent fill for this product.

No valid value in the SPL2SMP product is equal to the values that represent fill. If any exceptions should exist in the future, the SPL2SMP 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 SPL2SMP 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 element OrbitMeasuredLocation/halfOrbitStartDateTime.
  • The character string stored in metadata element Extent/rangeEndingDateTime will match the character string stored in metadata element OrbitMeasuredLocation/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 in OrbitMeasuredLocation/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 5 lists the acronyms and abbreviations used in this document.

Table 5. Acronyms and Abbreviations
Abbreviation Definition
Char 8-bit character
IGBP International Geosphere-Biosphere Programme
Int8 8-bit (1-byte) signed integer
Int16 16-bit (2-byte) signed integer
Int32 32-bit (4-byte) signed integer
Float32 32-bit (4-byte) floating-point integer
Float64 64-bit (8-byte) floating-point integer
H-pol Horizontally polarized
N/A Not Applicable
NF Number of frozen ground pixels
NL Number of land pixels
NT Number of thawed land pixels
NW Number of water pixels
SI International System of Units
SPL2SMP SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture
SPS Science Production Software
T1, T2 Threshold 1, Threshold 2
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
VWC Vegetation Water Content