Data Fields - SMAP L3 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Version 5

This page provides a description of all data fields within the SMAP L3 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture (SPL3SMP) product. The data are grouped into three main HDF5 groups:

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

Soil_Moisture_Retrieval_Data _[AM | PM]

Table 1 describes the data fields of a typical SPL3SMP file/granule.

Note: Data field names in the PM group are appended with _pm, such as EASE_column_index_pm.

Table 1. SPL3SMP Data Fields
Data Field Name Precision Byte Unit Valid Min Valid Max Fill/Gap Value Derivation Method(s)**
EASE_column_index Uint16 2 N/A 0 963  65534 2
EASE_row_index Uint16 2 N/A 0 405  65534 2
albedo Float32 4 N/A 0.0 1.0 -9999.0 6
boresight_incidence Float32 4 Degree 0.0 90.0 -9999.0 1
freeze_thaw_fraction Float32 4 N/A 0.0 1.0 -9999.0 6
grid_surface_status Uint16 2 N/A 0 1 65534 6
landcover_class Uint8 1 N/A 0 16 254 6
landcover_class_fraction Float32 1 N/A 0.0 1.0 -9999.0 6
latitude Float32 4 Degree -90.0 +90.0 -9999.0 2
latitude_centroid Float32 4 Degree -90.0 +90.0 -9999.0 1
longitude Float32 4 Degree -180.0 +180.0 -9999.0 2
longitude_centroid Float32 4 Degree -180.0 179.999 -9999.0 1
radar_water_body_fraction Float32 4 N/A 0.0 1.0 -9999.0 6
retrieval_qual_flag Uint16 2 N/A 0 65,536 65534 4
roughness_coefficient Float32 4 N/A 0.0 1.0 -9999.0 6
soil_moisture Float32 4 cm3/cm3 0.02 0.5 -9999.0 4
soil_moisture_error Float32 4 cm3/cm3 0.0 0.2 -9999.0 4 or 6
static_water_body_fraction Float32 4 N/A 0.0 1.0 -9999.0 6
surface_flag Uint16 2 N/A 0 65,536 65534 4
surface_temperature Float32 4 Kelvin 0.0 350.0 -9999.0 6
surface_water_fraction_mb_h Float32 4 N/A 0.0 1.0 -9999.0 6
surface_water_fraction_mb_v Float32 4 N/A 0.0 1.0 -9999.0 6
tb_3_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 N/A
tb_4_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 N/A
tb_h_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 3
tb_h_uncorrected Float32 4 Kelvin 0.0 330.0 -9999.0 1
tb_qual_flag_3 Uint16 2 N/A 0 65,536 65534 4
tb_qual_flag_4 Uint16 2 N/A 0 65,536 65534 4
tb_qual_flag_h Uint16 2 N/A 0 65,536 65534 4
tb_qual_flag_v Uint16 2 N/A 0 65,536 65534 4
tb_time_seconds Float64 8 Second -999999.9 9.4E8 -9999.0 1
tb_time_utc Char24 24 N/A 2014-10-31T
00:00:00.000Z
N/A 16777214 1
tb_v_corrected Float32 4 Kelvin 0.0 330.0 -9999.0 3
tb_v_uncorrected Float32 4 Kelvin 0.0 330.0 -9999.0 1
vegetation_opacity Float32 4 N/A -999999.9 999999.9 -9999.0 6
vegetation_water_content Float32 4 kg/m2 -999999.9 999999.9 -9999.0 6

** Derivation methods are:

  1. From SPL1CTB
  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 SPL2SMP processing software
  5. Available only with option algorithms that use two polarization channels
  6. From external ancillary data whose location and time stamp coincide with those of the input data

Data Field Definitions [top]

EASE_column_index

The column index of the 36 km grid cell that contains the associated data.

EASE_row_index

The row index of the 36 km 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 36 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).

landcover_class

An enumerated type that specifies the most common landcover class in the grid cell based on the IGBP landcover map. The array order is longitude (ascending), followed by latitude (descending), and followed by IGBP land cover type descending dominance (only the first three types are listed).

Table 2 provides a description of MODIS IGBP classes and the precentage of each land type.

Class Description Percentage
Table 2. MODIS IGBP Land Classification and Percentage
0 Water -
1 Evergreen Needleleaf Forest 3.96
2 Evergreen Broadleaf Forest 10.04
3 Deciduous Needleleaf Forest 0.63
4 Deciduous Broadleaf Forest 1.59
5 Mixed Forests 4.69
6 Closed Shrublands 0.55
7 Open Shrublands 18.26
8 Woody Savannas 7.52
9 Savannas 6.97
10 Grasslands 9.27
11 Permanent Wetlands 0.22
12 Croplands 8.95
13 Urban and Built-Up 0.50
14 Cropland/Natural Vegetation Mosaic 2.10
15 Snow and Ice 11.04
16 Barren or Sparsely Vegetated

13.70

landcover_class_fraction

The fraction of the grid cell that contains the most common land cover in that area based on the IGBP landcover map.

Table 2 provides a description of MODIS IGBP classes and the precentage of each land type.

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 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 grid cell.

radar_water_body_fraction

The fraction of the area of the 36 km grid cell that is covered by water based on the radar detection algorithm.

retrieval_qual_flag

Bit flags that record the conditions and the quality of the retrieval algorithms that generate soil moisture for the grid cell.

Table 3. 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 36 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.

static_water_body_fraction

The fraction of the area of the 36 km grid cell that is covered by static water based on a Digital Elevation Map.

surface_flag

Bit flags that record ambient surface conditions for the grid cell.

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)

0.05 0.10 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)

0.05 0.10 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: 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 36 km grid cell calculated with an adjustment for the presence of water bodies.

tb_4_corrected

Fourth stokes parameter for each 36 km grid cell calculated with an adjustment for the presence of water bodies.

tb_h_corrected

Horizontal polarization brightness temperature in 36 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 3rd Stokes brightness temperature within each grid cell.

tb_qual_flag_h

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

tb_qual_flag_v

Bit flags that represent the quality of the 3rd Stokes 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 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 grid cell in UTC.

tb_v_corrected

Vertical polarization brightness temperature in 36 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

The measured opacity of the vegetation in the grid cell.

Estimated vegetation opacity at 36 km spatial scale, as returned by the SPL2SMP processing software when one of the option algorithms 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

vegetation_water_content

Representative measure of water in the vegetation within the 36 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 SPL3SMP product when the SPL3SMP 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 Science Production Software (SPS) executables that generate the SMAP SPL3SMP 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 SPL3SMP 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 SPL1CTB 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 SPL3SMP product is equal to the values that represent fill. If any exceptions should exist in the future, the SPL3SMP 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 SPL3SMP 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 SPL1CTB 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
SPL3SMP SMAP L3 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