Data Fields - SMAP Enhanced L3 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Version 1

This page provides a description of all data fields within the SMAP Enhanced L3 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture (SPL3SMP_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 _[AM | PM]

Table 1 describes the data fields of a typical SPL3SMP_E file/granule.

Table 1. SPL3SMP_E Data Fields
Data Field Name Precision Byte Unit Valid Min Valid Max Fill/Gap Value Derivation Method(s)**
EASE_row_index Uint16 2 N/A 0 405 (Global) 65534 2
EASE_col_index Uint16 2 N/A 0 963 (Global) 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
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 +180.0 -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 3.0 -9999.0 6
soil_moisture Float32 4 cm3/cm3 0.02 0.5 -9999.0 4
soil_moisture_error Float32 4 cm3/cm3 0.01 0.55 -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 253.15 313.15 -9999.0 6
tb_3_corrected Float32 4 Kelvin -50 50 -9999.0 N/A
tb_4_corrected Float32 4 Kelvin -50 50 -9999.0 N/A
tb_h_corrected Float32 4 Kelvin 0.0 340.0 -9999.0 3
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 0 N/A -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 0.0 340.0 -9999.0 3
vegetation_opacity Float32 4 N/A 0.01 5.00 -9999.0 6
vegetation_water_content Float32 4 kg/m2 0 30.0 -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_col_index

Column index of a 36 km EASE-Grid 2.0 cell. In most grid cells, both fore-looking SPL1CTB data and aft-looking SPL1CTB data are available for soil moisture retrieval. But when one group (e.g., fore-looking group) is not available, the GridCol parameter of the other group (e.g., aft-looking group) will be written into this parameter.

EASE_row_index

Row index of a 36 km EASE-Grid 2.0 cell. In most grid cells, both fore-looking SPL1CTB data and aft-looking SPL1CTB data are available for soil moisture retrieval. But when one group (e.g., fore-looking group) is not available, the GridRow parameter of the other group (e.g., aft-looking group) will be written into this parameter.

albedo

Single-scattering albedo at 36 km spatial scale. Note that this parameter is the same 'omega' parameter in the 'tau-omega' model for a given polarization channel.

boresight_incidence

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of incidence angles of SPL1BTB 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.

freeze_thaw_fraction

Freeze/thaw fraction at 36 km spatial scale. If there are NF frozen ground pixels and NT thawed land pixels within a 36 km grid cell, this parameter refers to the fraction of NF / (NF + NT). At present the SPL2SMP processing software can be configured to provide this parameter from a dynamic ancillary data database or from the SMAP SPL2SMA product.

landcover_class

The first three most dominant land cover classes according to the IGBP land cover map. The relative dominance is determined based on ranking among land cover classes using statistical mode.

landcover_class_fraction

The fractions of the first three most dominant land cover classes according to the IGBP land cover map. The relative dominance is determined based on ranking among all land cover classes using statistical mode. For example, if there are N1 pixels that correspond to first class and there are NT pixels comprising all land cover classes within a 36 km grid cells, the corresponding percentage refers to (N1 / NT).

latitude

Latitude of the center of the 36 km EASE-Grid 2.0 cell located at (GridRow,GridCol).

latitude_centroid

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of latitudes of SPL1BTB observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

longitude

Longitude of the center of a 36 km EASE-Grid 2.0 cell located at (GridRow,GridCol).

longitude_centroid

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of longitudes of SPL1BTB observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

radar_water_body_fraction

Radar-derived water body fraction at 36 km spatial scale. If there are NW water pixels and NL land pixels within a 36 km grid cell, this parameter refers to the fraction of NW / (NW + NL). Note that NW is the number of water pixels regardless of their temporal span – NW captures both static water pixels and transient water pixels.

retrieval_qual_flag

A 16-bit integer field whose binary representation consists of bits that indicate whether retrieval is performed or not at a given 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 in Table 2. Flag is set based on value of bit 7 of surface_flag (Radiometer F/T).

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

Roughness coefficient at 36 km spatial scale. Note that this parameter is the same 'h' coefficient in the 'tau-omega' model for a given polarization channel.

soil_moisture

Daily global composite of the estimated soil moisture at 36 km spatial scale, as returned by the SPL2SMP processing software. The valid minimum and maximum below are subject to further analysis on real data.

soil_moisture_error

Estimated '1-sigma' error of the soil_moisture output parameter. The valid minimum and maximum are subject to further analysis on real data.

static_water_body_fraction

Static water body fraction at 36 km spatial scale. If there are NW water pixels and NL land pixels within a 36 km grid cell, this parameter refers to the fraction of NW / (NW + NL). Note that NW is the number of water pixels regardless of their temporal span – NW captures both static water pixels and transient water pixels.

surface_flag

A 16-bit integer field whose binary representation consists of bits that indicate the presence or absence of certain surface conditions at a grid cell. In Table 10, a '0' indicates the presence of a surface condition favorable to soil moisture retrieval. Each surface condition is numerically compared against two non-negative thresholds: T1 and T2, where T1 < T2. In most cases, when a surface condition is found to be below T1, retrieval is attempted and flagged for recommended quality. Between T1 and T2, retrieval is still attempted but flagged for uncertain quality. Above T2, retrieval is skipped. A summary of surface conditions and their thresholds are listed below. Table 3 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 3. 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)

* SMAP FT flags are presently validated only for land regions north of 45°N latitude. For details, refer to the SMAP Level-3 Freeze/Thaw Validated Assessment Report.

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

Soil temperature (averaged over the top 5-cm soil layer) at 36 km spatial scale. This parameter is used as input ancillary data parameter to the SPL2SMP processing software for both baseline and option algorithms. The valid minimum and maximum are subject to further analysis on real data.

tb_3_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of SPL1BTB vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to SPL2SMP inversion.

tb_4_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of SPL1BTB vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to SPL2SMP inversion.

tb_h_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of SPL1BTB horizontally polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to SPL2SMP inversion.

tb_qual_flag_3

A 16-bit or two-byte binary number formed by applying a Boolean 'AND' operation between the same parameters from both fore- and aft-looking groups in the input SPL1CTB granule. A '0' indicates that both the fore-looking and aft-looking SPL1CTB observations satisfy a given quality criterion described in SPL1BTB's tb_qual_flag_3 output parameter; a '1' indicates that the same criterion is violated by either fore-looking or aft-looking (or both) SPL1CTB observations. Bit position '0' refers to the least significant digit.

tb_qual_flag_4

A 16-bit or two-byte binary number formed by applying a Boolean 'AND' operation between the same parameters from both fore- and aft-looking groups in the input SPL1CTB granule. A '0' indicates that both the fore-looking and aft-looking SPL1CTB observations satisfy a given quality criterion described in SPL1BTB's tb_qual_flag_4 output parameter; a '1' indicates that the same criterion is violated by either fore-looking or aft-looking (or both) SPL1CTB observations. Bit position '0' refers to the least significant digit.

tb_qual_flag_h

A 16-bit or two-byte binary number formed by applying a Boolean 'AND' operation between the same parameters from both fore- and aft-looking groups in the input SPL1CTB granule. A '0' indicates that both the fore-looking and aft-looking SPL1CTB observations satisfy a given quality criterion described in SPL1BTB's tb_qual_flag_h output parameter; a '1' indicates that the same criterion is violated by either fore-looking or aft-looking (or both) SPL1CTB observations. Bit position '0' refers to the least significant digit.

tb_qual_flag_v

A 16-bit or two-byte binary number formed by applying a Boolean 'AND' operation between the same parameters from both fore- and aft-looking groups in the input SPL1CTB granule. A '0' indicates that both the fore-looking and aft-looking SPL1CTB observations satisfy a given quality criterion described in SPL1BTB's tb_qual_flag_v output parameter; a '1' indicates that the same criterion is violated by either fore-looking or aft-looking (or both) SPL1CTB observations. Bit position '0' refers to the least significant digit.

tb_time_seconds

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the average of UTC acquisition times of SPL1BTB 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 on January 1, 2000 UT).

tb_time_utc

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the average of UTC acquisition times, in ASCII representation, of SPL1BTB observations whose boresights fall within a 36 km EASE-Grid 2.0 cell.

tb_v_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input SPL1CTB granule. The resulting parameter thus describes the weighted average of SPL1BTB vertically polarized brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to SPL2SMP inversion.

vegetation_opacity

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

The valid minimum and maximum are subject to further analysis on real data.

vegetation_water_content

Vegetation water content at 36 km spatial scale. This parameter is used as input ancillary data parameter to the SPL2SMP processing software when the baseline algorithm is used. The valid minimum and maximum are subject to further analysis on real data.

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 4 lists the acronyms and abbreviations used in this document.

Table 4. 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 water pixels
NT Number of thawed land pixels
NW Number of land 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