Data Fields - SMAP Enhanced L3 Radiometer Global and Northern Hemisphere Daily 36 km EASE-Grid Freeze/Thaw State, Version 2

This page provides a description of all data fields within the SMAP Enhanced L3 Radiometer Global and Northern Hemisphere Daily 36 km EASE-Grid Freeze/Thaw State (SPL3FTP_E) product. The data are grouped into two main HDF5 groups depending on the projection (global or polar):

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


Freeze_Thaw_Retrieval_Data_[Global | Polar] 

Table 1 describes the data fields of a typical SPL3FTP_E global cylindrical or north polar granule. Data element arrays are three dimensional, with the exception of transition_direction and transition_state_flag arrays, which are two 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 Freeze_Thaw_Retrieval_Data_Global and Freeze_Thaw_Retrieval_Data_Polar
Data Field Name Shape Concept Byte Signed Unit Min Max Fill/Gap Value
EASE_column_index AMPM_LatCell_LonCell_Array integer uint16 2 N/A 0 65535 65534
EASE_row_index AMPM_LatCell_LonCell_Array integer uint16 2 N/A 0 65535 65534
FT_SCV_threshold AMPM_LatCell_LonCell_Array string float32 4 N/A 0 330 -9999.0
altitude_dem AMPM_LatCell_LonCell_Array real float32 4 m 0.0 999999.9 -9999.0
altitude_std_dev AMPM_LatCell_LonCell_Array real float32 4 m 0.0 1000.0 -9999.0
data_sampling_density AMPM_LatCell_LonCell_Array real float32 4 km 0.0 2.0 -9999.0
freeze_reference AMPM_LatCell_LonCell_Array real float32 4 dB -5 5 -9999.0
freeze_reference_date AMPM_LatCell_LonCell_Array string char 10 N/A 2013-01-01 2023-12-31 -9999.0
freeze_thaw AMPM_LatCell_LonCell_Array boolean uint8 1 N/A 0 1 254
freeze_thaw_time_seconds AMPM_LatCell_LonCell_Array real float64 8 seconds -999999.9 999999.9 -9999.0
freeze_thaw_time_utc AMPM_LatCell_LonCell_Array string char 13 N/A 00:00:00.000Z 00:00:00.000Z N/A
freeze_thaw_uncertainty AMPM_LatCell_LonCell_Array real float32 4 N/A -999999.9 999999.9 -9999.0
landcover_class AMPM_LatCell_LonCell_Array enum uint8 1 n/a 0 16 254
latitude AMPM_LatCell_LonCell_Array real float32 4 degrees -90 90 N/A
longitude AMPM_LatCell_LonCell_Array real float32 4 degrees -180 180 N/A
normalized_polarization_ratio AMPM_LatCell_LonCell_Array string float32 4 N/A -5.0 5.0 -9999.0
open_water_body_fraction AMPM_LatCell_LonCell_Array real float32 4 normalized 0.0 1.0 -9999.0
reference_image_threshold AMPM_LatCell_LonCell_Array real float32 4 normalized -999999.9 999999.9 -9999.0
retrieval_qual_flag AMPM_LatCell_LonCell_Array bit flag uint32 4 N/A N/A N/A 65534
surface_flag AMPM_LatCell_LonCell_Array bit flag uint32 4 N/A N/A N/A 65534
tbh_error AMPM_LatCell_LonCell_Array real Uint8 2 normalized 0 1 -9999.0
tbh_mean AMPM_LatCell_LonCell_Array real float32 4 Kelvin -999999.9 999999.9 -9999.0
tbh_qual_flag AMPM_LatCell_LonCell_Array bit flag Uint16 2 N/A N/A N/A 65534
tbv_error AMPM_LatCell_LonCell_Array real float32 4 Kelvin -999999.9 999999.9 -9999.0
tbv_mean AMPM_LatCell_LonCell_Array real float32 4 Kelvin -999999.9 999999.9 -9999.0
tbv_qual_flag AMPM_LatCell_LonCell_Array bit flag uint32 4 N/A N/A N/A N/A
thaw_reference AMPM_LatCell_LonCell_Array real float32 4 dB -5 5 -9999.0
thaw_reference_date AMPM_LatCell_LonCell_Array string char 10 N/A 2013-01-01 2023-12-31 N/A
transition_direction LatCell_LonCell_Array boolean uint8 1 N/A 0 2 254
transition_state_flag LatCell_LonCell_Array boolean uint8 1 N/A 1 2 254

Metadata [top]

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

Data Field Definitions [top]

altitude_dem

The Earth surface elevation within the grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

altitude_std_dev

The standard deviation of the Earth surface elevation within the grid cell.  This element provides a surface roughness measure. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

FT_SCV_threshold

Threshold for the SCV algorithm based on reference V-pol TB to differentiate between freeze and thaw conditions. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

landcover_class

An enumerated type that specifies the predominant surface vegetation found in the grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array. See Table 2.

Table 2. Landcover Classification Values
Value Description
0 Water
1 Evergreen needleleaf forest
2 Evergreen broadleaf forest
3 Deciduous needleleaf forest
4 Deciduous broadleaf forest
5 Mixed forest
6 Closed shrubland
7 Open shrubland
8 Woody savanna
9 Savanna
10 Grassland
11 Permanent wetland
12 Croplands
13 Urban and built-up
14 Cropland/natural vegetation mosaic
15 Permanent snow and ice
16 Barren or sparsely vegetated
>16 TBD

open_water_body_fraction

Fraction of the area of the grid cell surface covered by open water.  Open water areas do not have vegetation at or on the water surface. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

EASE_column_index

The column index of the 36 km EASE-Grid 2.0 cell that contains the associated data. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

EASE_row_index

The row index of the 36 km EASE-Grid 2.0 cell that contains the associated data. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

data_sampling_density

Total number of radiometer data samples in the grid cell.  The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_reference

Reference normalized polarization ratio value used as a basis to indicate frozen conditions. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_reference_date

Date of the data used to determine the reference freeze condition. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_thaw

Boolean that indicates whether soil within cell is frozen or thawed.  A value of zero value implies thawed conditions, a value of 1 implies frozen. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_thaw_time_seconds

Time of the freeze-thaw determination for this particular element in seconds from the standard epoch. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_thaw_time_utc

Time of the freeze-thaw determination for this particular element in UTC. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

freeze_thaw_uncertainty

Uncertainty measure for the recorded freeze-thaw result.  Method to determine uncertainty is TBD. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

latitude

Latitude of the center of the Earth based grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

longitude

Longitude of the center of the Earth based grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

normalized_polarization_ratio
Normalized Tb polarization ratio at the Earth based grid cell, defined as (TBH-TBV)/(TBH+TBV). The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

reference_image_threshold

Threshold based on reference freeze and thaw to differentiate between freeze and thaw conditions. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

retrieval_qual_flag

Sequence of bit flags that indicate the conditions and the quality of the freeze-thaw retrieval. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array. See Table 3.

Name Bit Position Interpretation of Values (0:off, 1:on)
Table 3. Retrieval Quality Bit Flag Definitions
FT retrieval attempted 0 0: Retrieval was attempted
1: Retrieval not attempted due to excess water fraction in cell (nominally > 50%)
FT high water caution flag 1 0: Water body fraction lower than threshold (20%)
1: Water body fraction between 20-50%
FT permanent ice retrieval caution flag 2 0: Freeze-thaw retrieval not over permanent ice
1: Freeze-thaw retrieval was attempted over permanent ice landcover
FT SCV low correlation caution flag 3 0: FT SCV retrieval was attempted where the absolute value of SCV correlation is > 0.5
1: FT SCV retrieval was attempted where the absolute value of SCV correlation is ≤ 0.5
AMSR-E/TB false flag mitigation caution flag 4 0: No AMSR-E or TB mitigation was used
1: AMSR-E or TB mitigation was used to correct retrieved FT state
Reserved 5-15 0: Always clear

surface_flag

Bit flags that record ambient surface conditions for the grid cell. See Table 4.

Table 4. Surface Condition Quality Bit Flag Definitions

Bit Position

Bit Definition

Bit Value and Interpretation

0

Static Water Body Flag

0: The fraction of the 36 km grid cell area that is over a permanent water body is less than metadata element PermanentWaterBodyThreshold. 

1: The fraction of the 36 km grid cell area that is over a permanent water body is greater than or equal to metadata element PermanentWaterBodyThreshold. 

1

Radar Water Body Detection Flag

0: Transient water body not detected within 36 km cell

1: Transient water body detected within 36 km cell

2

Coastal Proximity Flag

0: Cell is more than 1 grid cell from coastline

1: Cell is within on grid cell of coastline

3

Urban Area Flag

0: The fraction of the 36 km grid cell area that is over urban development is less than metadata element UrbanAreaThreshold.

1: The fraction of the 36 km grid cell area that is over urban development is greater than or equal to metadata element UrbanAreaThreshold.

4

Precipitation Flag

0: No significant precipitation detected within the 36 km grid cell when data were being acquired.

1: Precipitation greater than threshold was detected within the 36 km grid cell.

5

Snow/Ice Flag (dynamic)

0: Snow or ice cover less than threshold was detected within the 36 km grid cell. 

1: Snow and/or ice greater than threshold were detected within the 36 km grid cell.

6

Permanent Snow/Ice Flag

0: Cell landcover (from IGBP) is not dominantly permanent snow or ice

1: Cell landcover (from IGBP) is dominantly permanent snow or ice

7

Frozen Ground Flag (from SMAP radiometer FT algorithm)

0: No frozen ground detected within the 36 km grid cell. 

1: Frozen ground detected within the 36 km grid cell.

8

Frozen Ground Flag (from GMAO TSURF)

0: No frozen ground detected within the 36 km grid cell.  TSURF > 0C.

1: Frozen ground detected within the 36 km grid cell. TSURF < 0C.

9

Mountainous Terrain Flag

0: The variability of land elevation in the 36 km grid cell is less than metadata element MountainousTerrainThreshold.

1: The variability of land elevation in the 36 km grid cell is greater than or equal to metadata element MountainousTerrainThreshold.

10

Dense Vegetation Flag

0: The vegetation density within the 36 km grid cell is less than metadata element DenseVegetationThreshold.

1: The vegetation density within the 36 km grid cell area is greater than or equal to  metadata element DenseVegetationThreshold.

11

Nadir Swath Flag

0: Data within the the grid cell were not acquired in the nadir region of the swath where sigma0s may not meet the 36 km resolution requirement.

1: A significant fraction (TBD) of the 36 km grid cell data were acquired within the nadir region of the swath where sigma0s may not meet the 36 km resolution requirement.

12-15

Always clear
Note: Bits shown with strikethrough in this table (1-3, 7, 10, 11) are not used in the SPL3FTP_E product, and are always set to 0.

thaw_reference

Reference normalized polarization ratio value used as a basis to indicate thawed conditions. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

thaw_reference_date

Date of the data used to determine the reference thawed conditon. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

transition_direction

Boolean that indicates transitional direction.  2 indicates AM frozen, PM thawed, 1 indicates AM thawed, PM frozen. Value is always zero if not in transition state.

transition_state_flag

Boolean that indicates whether soil is in transitional state from AM to PM on the same day. 1 indicates state is not in transition (does not change from AM to PM), 2 indicates state is in transition (AM and PM states are different).

tbh_error
Overall error measure for H-pol brightness temperature within the grid cell, includes calibration, RFI and contamination effects. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

tbh_mean
Mean of H-pol brightness temperature in the 36 km Earth grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

tbh_qual_flag
Bit flags that represent the quality of the horizontal polarization brightness temperature within each grid cell. See Table 5.

Table 5. TB Quality Bit Definitions
Flag Definition Bit Position Bit Value and Interpretation
Mean vertical polarization quality flag 0 0: The mean of the forward looking and aft looking vertical polarization Tb has acceptable quality.
1: The mean of the forward looking and aft looking vertical polarization Tb does not have acceptable quality.
Mean vertical polarization range flag 1 0: The mean of the forward looking and aft looking vertical polarization Tb falls within the expected range.
1: The mean of the forward looking and aft looking vertical polarization Tb is out of range.
Mean vertical polarization RFI detected flag 2 0: Insignificant RFI was detected in the mean of the forward looking and aft looking vertical polarization Tb.
1: RFI was detected in the mean of the forward looking and aft looking vertical polarization Tb.
Mean vertical polarization RFI repair flag 3 0: Some components of the mean of the forward looking and aft looking vertical polarization Tb are based on corrections for RFI contamination.
1: Unable to correct the mean of the forward looking and aft looking vertical polarization Tb for RFI contamination.
Mean vertical polarization NEDT flag 4 0: The mean vertical polarization Tb had acceptable NEDT.
1: NEDIT is unsuitably high for the mean vertical polarization Tb.
Vertical polarization direct sun correction flag 5 0: Direct sun correction was successful.
1: Direct sun correction was not successful.
Vertical polarization reflected sun correction flag 6 0: Reflected sun correction was successful.
1: Reflected sun correction was not successful.
Vertical polarization reflected moon correction flag 7 0: Reflected moon correction was successful.
1: Reflected moon correction was not successful.
Vertical polarization direct galaxy correction flag 8 0: Direct galaxy correction was successful.
1: Direct galaxy correction was not successful.
Vertical polarization reflected galaxy correction flag 9 0: Reflected galaxy correction was successful.
1: Reflected galaxy correction was not successful.
Vertical polarization atmospheric correction flag 10 0: Atmospheric correction was successful.
1: Atmospheric correction was not successful.
Vertical polarization Faraday rotation correction flag 11 0: Faraday rotation correction was successful.
1: Faraday rotation correction was not successful.
Vertical polarization null value bit 12 0: Tb has a valid value.
1: Tb has a null value.
Vertical polarization water correction 13 0: Water correction was not performed.
1: Water correction was performed.
Vertical polarization RFI check 14 0: TA minus TA_FILTERED was less than a threshold
1: TA minus TA_FILTERED was greater than a threshold
Vertical polarization RFI clean 15 0: TB was free of RFI
1: TB was RFI contaminated

tbv_error
Overall error measure for V-pol brightness temperature within the grid cell, includes calibration, RFI and contamination effects. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

tbv_mean
Mean of V-pol brightness temperature in the 36 km Earth grid cell. The AM (dimension AMPM:0) and PM (AMPM:1) observations are stored separately in the array.

tbv_qual_flag
Bit flags that represent the quality of the vertical polarization brightness temperature within each grid cell. See Table 5. 

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 SPL3FTP_E Product when the SPL3FTP_E 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 SPL3FTP_E 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 SPL3FTP_E 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 SPL1BTB product. If only some of the input that contributes to a particular grid cell is fill data, the Level SPL3FTP_E SPS will most likely be able to generate some output. However, some portion of the SPL3FTP_E 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 SPL3FTP_E product is equal to the values that represent fill. If any exceptions should exist in the future, the SPL3FTP_E 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 SPL3FTP_E 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 SPL3FTP_E 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.

Notations [top]

Table 6 lists the notations used in this document.

Table 6. Notation Definitions
Notation Definition
Int8 8-bit (1-byte) signed integer
Int16 16-bit (2-byte) signed integer
Int32 32-bit (4-byte) signed integer
Uint8 8-bit (1-byte) unsigned integer
Uint16 16-bit (2-byte) unsigned integer
Float32 32-bit (4-byte) floating-point integer
Float64 64-bit (8-byte) floating-point integer
Char 8-bit character
H-pol Horizontally polarized
V-pol Vertically polarized