Data Fields - SMAP Enhanced L2 Radiometer Half-Orbit 9 km EASE-Grid Soil Moisture, Version 3

 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:

  • Metadata
  • Soil_Moisture_Retrieval_Data

For a description of metadata fields for this product, refer to the Product Specification 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
albedo_option3 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
bulk_density Float32 4 N/A 0.0 3.0 -9999.0 N 6
clay_fraction Float32 4 N/A 0.0 1.0 -9999.0 N 6
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 7
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 +180.0 -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
roughness_coefficient Float32 4 N/A 0.0 3.0 -9999.0 N 6
roughness_coefficient_option3 Float32 4 N/A 0.0 3.0 -9999.0 N 6
soil_moisture Float32 4 m3/m3 0.02 Soil Porosity -9999.0 N 4
soil_moisture_error Float32 4 m3/m3 0.02 Soil Porosity -9999.0 N 4 or 6
soil_moisture_option1 Float32 4 m3/m3 0.02 Soil Porosity -9999.0 N 4
soil_moisture_option2 Float32 4 m3/m3 0.02 Soil Porosity -9999.0 N 4
soil_moisture_option3 Float32 4 m3/m3 0.02 Soil Porosity -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 253.15 313.15 -9999.0 N 6
surface_water_fraction_mb_h Float32 4 Kelvin 0.0 1.0 -9999.0 N 1
surface_water_fraction_mb_v Float32 4 Kelvin 0.0 1.0 -9999.0 N 1
tb_3_corrected Float32 4 Kelvin -50.0 50.0 -9999.0 N 1
tb_4_corrected Float32 4 Kelvin -50.0 50.0 -9999.0 N 1
tb_h_corrected Float32 4 Kelvin 0.0 340.0 -9999.0 N 1
tb_h_uncorrected Float32 4 Kelvin 0.0 340.0 -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 0 N/A -9999.0 N 1
tb_time_utc Char24 24 N/A
2015-01-31T
00:00:00.000Z
N/A 16777214 N 1
tb_v_corrected Float32 4 Kelvin 0.0 340.0 -9999.0 N 1
tb_v_uncorrected Float32 4 Kelvin 0.0 340.0 -9999.0 N 1
vegetation_opacity Float32 4 N/A 0.01 5.00 -9999.0 N 6
vegetation_opacity_option1 Float32 4 N/A 0.01 5.00 -9999.0 N 6
vegetation_opacity_option2 Float32 4 N/A 0.01 5.00 -9999.0 N 6
vegetation_opacity_option3 Float32 4 N/A 0.01 5.00 -9999.0 N 5
vegetation_water_content Float32 4 kg/m2 0 30.0 -9999.0 N 6

* Derivation methods are:

  1. From Level-1C brightness temperature data
  2. From 9-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 time stamp coincide with those of the input data
  7. Nearest-neighbor interpolation

Data Field Definitions [top]

EASE_column_index

Column index of a 9-km EASE 2.0 grid cell. In most grid cells, both fore-looking L1C_TB_E data and aft-looking L1C_TB_E 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 9-km EASE 2.0 grid cell. In most grid cells, both fore-looking L1C_TB_E data and aft-looking L1C_TB_E 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 9-km grid posting. Note that this parameter is the same ‘omega’ parameter in the ‘tau-omega’ model for a given polarization channel.

albedo_option3
Single-scattering albedo at 9-km grid posting derived from landcover-based table used for the Modified Dual-Channel Algorithm (MDCA). Note that this parameter is the same 'omega' parameter in 'tau-omega' model when used in MDCA.

boresight_incidence

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of incidence angles of L1B_TB_E observations whose boresights fall within a 9-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.

bulk_density
Bulk density at 9-km grid posting.

clay_fraction
Clay fraction at 9-km grid posting.

freeze_thaw_fraction

Freeze/thaw areal fraction at 9-km grid posting. The fraction is computed based on the number of frozen land pixels and thawed land pixels reported on the 3-km global cylindrical EASE-Grid 2.0 projection in the SMAP Level 2 Active Soil Moisture Product (L2_SM_A). If there are NF frozen ground pixels and NT thawed land pixels within a 9-km grid cell, this parameter refers to the fraction of NF / (NF + NT). At present the L2_SM_P processing software can be configured to provide this parameter from a dynamic ancillary data database or from the SMAP L2_SM_A product. Since the failure of the SMAP radar this field has been derived from external soil temperature ancillary data.

grid_surface_status
Surface type (land or water) as determined by the antenna boresight location.

latitude

Latitude of the center of the Earth based grid cell.

latitude_centroid

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of latitudes of L1B_TB_E observations whose boresights fall within a 9-km EASE-Grid 2.0 cell.

longitude

Longitude of the center of the Earth based grid cell.

longitude_centroid

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of latitudes of L1B_TB_E observations whose boresights fall within a 9-km EASE-Grid 2.0 cell.

radar_water_body_fraction

Radar-derived water body areal fraction at 9-km grid posting. The fraction is computed based on the number of water pixels and land pixels reported on the 3-km global cylindrical EASE-Grid 2.0 projection in the SMAP Level 2 Active Soil Moisture Product (L2_SM_A). If there are NW water pixels and NL land pixels within a 9-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. Since the failure of the SMAP radar this field has been set to the static_water_body_fraction field.

retrieval_qual_flag, retrieval_qual_flag_option[1-3]

A 16-bit binary string of 1’s and 0’s that indicate whether retrieval was performed or not at a given grid cell. When retrieval was 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. 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 3.

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 doesn't have recommended 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)

roughness_coefficient

Roughness coefficient at 9-km grid posting. Note that this parameter is the same 'h' coefficient int he 'tau-omega' model for a given polarization channel.

roughness_coefficient_option3
Roughness coefficient at 9-km grid posting derived from 3 km global map of 'h' created by special dual-channel retrieval. Note that this parameter is the same 'h' coefficient in the 'tau-omega' model when used in MDCA.

soil_moisture
The estimated soil moisture at 9-km grid posting, as returned by the SPL2SMP_E processing software. The soil_moisture field is internally linked to the soil_moisture_option2 output produced by the baseline algorithm.

soil_moisture_error

The estimated ‘1-sigma’ error of the soil_moisture output parameter. The valid minimum and maximum below are subject to further analysis on real data. This data field is currently filled with FillValue.

soil_moisture, soil_moisture_option[1-3]

The estimated soil moisture at 9-km grid posting, as returned by the L2_SM_P_E processing software. The soil_moisture field is internally linked to the output produced by the baseline algorithm (option 2 as of now). At present, the operational SPL2SMP Science Production Software (SPS) produces and stores soil moisture retrieval results from the three 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)
Modified Dual Channel Algorithm (MDCA) soil_moisture_option3 retrieval_qual_flag_option3

static_water_body_fraction

Static water body areal fraction at 9-km grid posting. The fraction is computed based on the number of water pixels and land pixels reported on a 250-meter grid. If there are NW water pixels and NL land pixels within a 9-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 when the original data were acquired.

surface_flag

A 16-bit binary string of 1’s and 0’s that indicate the presence or absence of certain surface conditions at a grid cell. In Table 4, 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 in Table 4. The surface_flag field is internally linked to the output produced by the baseline algorithm (option 2 as of now).

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
0.50
0: Water areal fraction ≤ T1 and IGBP wetland fraction < 0.50:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
1
Radar-derived Water Fraction
0.05
0.50
0: Water areal fraction ≤ T1 and IGBP wetland fraction < 0.50:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
2
Coastal Proximity
N/A
1.0
0: Distance to nearby significant water bodies > T2 (number of 36-km grid cells)
1: Otherwise
3
Urban Area
0.25
1.00
0: Urban areal fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
4
Precipitation
2.78e-04 (equivalent to
1.0 mm/hr)
7.06e-03 (equivalent to
25.4 mm/hr)
0: Precipitation fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
5
Snow
0.05
0.50
0: Snow areal fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
6
Permanent Ice
0.05
0.50
0: Ice areal fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
7
Frozen Ground* (from radiometer-derived FT state)
0.05
0.50
0: Freeze ground areal fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
8
Frozen Ground (from modeled effective soil temperature)

 
0.05
0.50
0: Freeze ground areal fraction ≤ T1:
  • Retrieval attempted for fraction ≤ T2
1: Otherwise:
  • Retrieval skipped for fraction > T2
9
Mountainous Terrain
0: Slope standard deviation ≤ T1
1: Otherwise
10
Dense Vegetation
5.0
30.0
0: Vegetation Water Content (VWC) ≤ T1:
  • Retrieval attemtped for VWC ≤ T2
1: Otherwise:
  • Retrieval skipped for VWC > T2
11
Nadir Region / Undefined
0 (not used in this product)
12-15
Undefined
0

surface_temperature

Effective soil temperature (average for the top 5-cm soil layer) at 9-km grid spacing. This calculated model parameter is used as an input ancillary data parameter to the L2_SM_P_E processing software for both baseline and option algorithms. The valid minimum and maximum below are subject to further analysis on real data.

It has come to our attention that this parameter is often mistaken for the physical temperature of the top soil layer. The designation “effective” signifies an attempt to capture the soil integrated temperature and canopy temperature in a single parameter, as is widely reported in the literature.  Depending on the actual emission sensing depth (which varies with soil moisture), this parameter usually does not coincide with a thermal physical temperature at a fixed depth (e.g. 5 cm or 10 cm).


surface_water_fraction_mb_h
Water fraction with the SMAP radiometer main-beam (mb) IFOV weighted by antenna gain pattern at the horizontal polarization.

surface_water_fraction_mb_v
Water fraction with the SMAP radiometer main-beam (mb) IFOV weighted by antenna gain pattern at the vertical polarization.

tb_3_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E 3rd Stokes polarized brightness temperatures whose boresights fall within a 9-km EASE-Grid 2.0 cell.

tb_4_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E 4th Stokes polarized brightness temperatures whose boresights fall within a 9-km EASE-Grid 2.0 cell.

tb_h_corrected

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E horizontally polarized brightness temperatures whose boresights fall within a 9-km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to L2_SM_P_E inversion.

tb_h_uncorrected
Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E horizontally polarized brightness temperatures prior to water correction whose boresights fall within a 9-km EASE-Grid 2.0 cell.

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 L1C_TB_E granule. A ‘0’ indicates that both the fore-looking and aft-looking L1C_TB_E observations satisfy a given quality criterion described in L1B_TB_E’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) L1C_TB_E observations. Bit position '0' refers to the least significant digit. Bit definitions are shown in Table 5.

Table 5. tb_qual_flag bit definitions
Bit Position Bit Value and Interpretation
0 0 = Observation has acceptable quality
1 = Observation does not have acceptable quality
1 0 = Observation within physical range
1 = Observation beyond physical range
2 0 = RFI was not detected in the observation
1 = RFI was detected in the observation
3 0 = RFI was detected and corrected in the observation
1 = RFI was detected but not correctable in the observation
4 0 = Observation had acceptable NEDT
1 = Observation did not have acceptable NEDT
5 0 = Direct sun correction was successful
1 = Direct sun correction was not successful
6 0 = Reflected sun correction was successful
1 = Reflected sun correction was not successful
0 = Reflected moon correction was successful
1 = Reflected moon correction was not successful
8 0 = Direct galaxy correction was successful
1 = Direction galaxy correction was not successful
9 0 = Reflected galaxy correction was successful
1 = Reflected galaxy correction was not successful
10  0 = Atmosphere correction was successful
1 = Atmosphere correction was not successful
11 intentionally left undefined
12 0 = Observation was a valid value
1 = Observation was a null value
13 0 = Observation was within half orbit
1 = Observation was outside half orbit
14 0 = TA minus TA_FILTERED was less than a threshold
1 = TA minus TA_FILTERED was greater than a threshold
15 0 = Observation was free of RFI
1 = Observation was RFI contaminated

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 L1C_TB_E granule. A ‘0’ indicates that both the fore-looking and aft-looking L1C_TB_E observations satisfy a given quality criterion described in L1B_TB_E’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) L1C_TB_E observations. Bit position '0' refers to the least significant digit. Bit definitions are shown in Table 5.

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 L1C_TB_E granule. A ‘0’ indicates that both the fore-looking and aft-looking L1C_TB_E observations satisfy a given quality criterion described in L1B_TB_E’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) L1C_TB_E observations. Bit position '0' refers to the least significant digit. Bit definitions are provided in Table 6.

Table 6. tb_qual_flag bit definitions
Bit Position Bit Value and Interpretation
0 0 = Observation has acceptable quality
1 = Observation does not have acceptable quality
1 0 = Observation within physical range
1 = Observation beyond physical range
2 0 = RFI was not detected in the observation
1 = RFI was detected in the observation
3 0 = RFI was detected and corrected in the observation
1 = RFI was detected but not correctable in the observation
4 0 = Observation had acceptable NEDT
1 = Observation did not have acceptable NEDT
5 0 = Direct sun correction was successful
1 = Direct sun correction was not successful
6 0 = Reflected sun correction was successful
1 = Reflected sun correction was not successful
0 = Reflected moon correction was successful
1 = Reflected moon correction was not successful
8 0 = Direct galaxy correction was successful
1 = Direction galaxy correction was not successful
9 0 = Reflected galaxy correction was successful
1 = Reflected galaxy correction was not successful
10  0 = Atmosphere correction was successful
1 = Atmosphere correction was not successful
11 0 = Faraday rotation correction was successful
1 = Faraday rotation correction was not successful
12 0 = Observation was a valid value
1 = Observation was a null value
13 0 = Water correcition was not performed
1 = Water correction was performed
14 0 = TA minus TA_FILTERED was less than a threshold
1 = TA minus TA_FILTERED was greater than a threshold
15 0 = Observation was free of RFI
1 = Observation was RFI contaminated

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 L1C_TB_E granule. A ‘0’ indicates that both the fore-looking and aft-looking L1C_TB_E observations satisfy a given quality criterion described in L1B_TB_E’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) L1C_TB_E observations. Bit position '0' refers to the least significant digit. Bit definitions are provided in Table 6.

tb_time_seconds

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the average of UTC acquisition times of L1B_TB_E observations whose boresights fall within a 9-km EASE-Grid 2.0 cell. The result is then expressed in J2000 seconds (the number of seconds since 12:00:00.000 on January 1, 2000 Barycentric Dynamical Time (TDB)).

tb_time_utc

Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the average of UTC acquisition times, in ASCII representation, of L1B_TB_E observations whose boresights fall within a 9-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 L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E vertically polarized brightness temperatures whose boresights fall within a 9-km EASE-Grid 2.0 cell. Wherever water fraction is below a threshold, water brightness temperature correction is applied to this parameter prior to L2_SM_P_E inversion.

tb_v_uncorrected
Arithmetic average of the same parameters found in the fore- and aft-looking groups in the input L1C_TB_E granule. The resulting parameter thus describes the weighted average of L1B_TB_E vertically polarized brightness temperatures prior to water correction whose boresights fall within a 9-km EASE-Grid 2.0 cell.

vegetation_opacity, vegetation_opacity_option[1-3]

The estimated vegetation opacity at 9-km grid posting, as returned by the L2_SM_P_E processing software. Note that this parameter is the same ‘tau’ parameter normalized by the cosine of the incidence angle in the ‘tau-omega’ model.. Single channel algorithms option 1 and option 2 calculate vegetation opacity or tau using the following equation:

tau-omega equation

where is a landcover-based parameter described in the SPL2SMP/SPL3SMP ATBD, VWC is vegatation water content in kg/m2 dervied from NDVI climatology, and θ is the incidence angle (= 40 degrees) for SMAP. 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. Vegetation_opacity_opion3 is not calculated by the equation above, but rather is retrieved directly along with soil moisture from the Modified Dual Channel Algorithm.

vegetation_water_content

Vegetation water content at 9-km grid posting. This parameter is used as input ancillary data parameter to the L2_SM_P_E processing software when the baseline algorithm is used. The valid minimum and maximum below are subject to further analysis on real data.

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_E SMAP Enhanced 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