Changes to this version include:

• Transitioned to Validated-Stage 2
• Calibration parameters were adjusted to reduce calibration jumps and drift previously present in the Beta-release; as a result, calibration now meets its less than 0.4 K/month stability back to 31 March 2015
• Additional bit-error checking was performed on Level-0 instrument telemetry

Version 2

2016-12-07 (10:31) to 2017-04-24 (11:00)

Version 2

2017-04-24 (10:56) to 2017-09-06 (16:52)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-03 (21:36) to 2017-11-14 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

Version 2

2017-12-10 (17:54) to 2018-03-14 (19:57)

2018-03-14 (15:51) to 2018-06-03 (23:50)

R15182

2019-08-15

2019-12-21 (11:56) to 2020-08-27 (21:26)

Changes to this version include:

• Transitioned to Validated-Stage 1
• Using SPL1BTB V2 data as input, inherited all changes and improvements of the new version

• Updated reflector thermal model
• Reflector emissivity value back to baseline
• All calibration coefficients updated back to 3/31/15
• Direct Galaxy quality flag changed: set when s/c nadir > 5 degrees
• Reflected Sun quality flag changed: set when specular solar theta <15 degrees
• Sea ice fraction computation implemented

2016-12-07 (10:31) to 2017-04-24 (08:32)

2017-04-24 (08:28) to 2017-09-06 (16:52)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-03 (21:36) to 2017-11-14 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2018-01-09 (21:35)

2017-12-10 (17:54) to 2018-03-14 (19:57)

2018-03-14 (15:51) to 2018-06-04 (17:04)

2018-03-14

2018-06-14 (15:50)

Changes to this version include:

• Added procedure to correct brightness temperatures for water/land contamination near coastlines. New data fields for this correction include: footprint_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_surface_corrected, and tb_v_surface_corrected.
• Improved Level-1 calibration coefficients and reflected galaxy correction. To refine reflected galaxy correction over ocean, NOAA NCEP ocean roughness data have been added (wind_direction_ancillary, wind_speed_ancillary).

On 2019-02-07, data files from 2018-12-22 to 2019-01-22 were reprocessed to include input sea surface temperature ancillary data that were inaccessible during the US government shutdown. Note that the lack of this input data had a minimal impact on brightness temperatures over the ocean.

On 2018-12-31, data files from 2019-01-01 to present experienced no science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January through December 2019.

Changes to this version include:

• An improved calibration methodology was applied to Level-1 brightness temperatures, which uses:
  • the internal instrument reference load (instead of the global ocean as in V4)
  • deep space measurements during monthly cold sky maneuvers and special cold sky maneuvers with stable open-ocean background to concurrently retrieve all calibration parameters
  • a longer temporal baseline of cold sky records.

Version changes include:

• Antenna Scan Angle (ASA) correction: new code examines the initial scan angle in each scan and flags any scan angle that falls out of the normal range as bad
• No change to product format, quality, or size

Changes to this version include:

• Transitioned to Validated-Stage 2
• Using SPL1BTB V2 Validated data as input, inherited all changes and improvements of the new version

• Uses updated SPL1BTB V3 Validated data as input
• Updated processing to produce SPL1CTB data files when partial half-orbit input files are present

Version 3

2015-03-31 (16:28) to 2017-04-23 (00:32)

Version 3

2017-04-23 (00:28) to 2017-09-06 (16:52)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-03 (21:36) to 2017-11-14 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2017-09-03

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-04 (17:04)

2018-06-14 (15:50)

On 2019-02-07, data files from 2018-12-22 to 2019-01-22 were reprocessed to include input sea surface temperature ancillary data that were inaccessible during the US government shutdown. Note that the lack of this input data had a minimal impact on brightness temperatures over the ocean.

On 2018-12-31, data files from 2019-01-01 to present experienced no science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January through December 2019.

Changes to this version include:

• An improved calibration methodology was applied to the input Level-1B radiometer brightness temperatures.
• The data algorithms, structure, content, or processor code are otherwise unchanged from the previous version.

Version 1

2015-03-31 (16:28) to 2017-04-24 (00:20)

2016-12-07

Version 1

2017-04-24 (00:16) to 2017-09-06 (16:52)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-04-24

2017-09-03 (21:36) to 2017-11-14 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2018-01-08 (23:26)

2017-10-26

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-04 (17:04)

2015-03-31 (16:28) to 2018-06-14 (13:22)

On 2019-02-07, data files from 2018-12-22 to 2019-01-22 were reprocessed to include input sea surface temperature ancillary data that were inaccessible during the US government shutdown. Note that the lack of this input data had a minimal impact on brightness temperatures over the ocean.

On 2018-12-31, data files from 2019-01-01 to present experienced no science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January through December 2019.

Changes to this version include:

• An improved calibration methodology was applied to the input Level-1B radiometer brightness temperatures.
• The data algorithms, structure, content, or processor code are otherwise unchanged from the previous version.

Changes to this version include:

• Uses SPL1CTB V2 Validated-Stage 1 data as input
• Corrects the retrieval quality flag error

2015-04-13 (00:41) to 2015-12-31 (23:18)

2015-03-31 (16:28) to 2016-12-07 (05:40)

Changes to this version include:

• Transitioned to Validated-Stage 2
• Uses updated SPL1CTB V3 Validated data as input

2015-03-31 (16:28) to 2017-04-23 (00:32)

Changes to this version include:

• Added 6:00 p.m. ascending half orbits, which provide:
  • More frequent regional/global coverage (critical in flood monitoring)
  • Soil moisture diurnal variability information (useful in data assimilation systems)
  • Consistency with other similar satellite-based soil moisture products
• Contains frozen ground flag (bit 7 of surface_flag) derived using Normalized Polarization Ration (NPR)-based SMAP passive freeze-thaw retrieval; replaces former SMAP radar-based freeze/thaw flag

2017-04-23 (00:28) to 2017-09-01 (23:39)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-02 (00:28) to 2017-10-25 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2017-09-02

2018-01-08 (23:26)

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-14 (07:38)

Changes to this version include:

• Level-1B water-corrected brightness temperatures are used in passive soil moisture retrieval. This procedure corrects for anomalous soil moisture values seen near coastlines in the previous version and should result in less rejected data due to waterbody contamination. Five new data fields accommodate this correction: grid_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_uncorrected, and tb_v_uncorrected.
• Improved depth correction for effective soil temperature used in passive soil moisture retrieval; new results are captured in the surface_temperature data field. This correction reduces the dry bias seen when comparing SMAP data to in situ data from the core validation sites.

• Frozen ground flag updated to reflect improved freeze/thaw detection algorithm, providing better accuracy; new results are captured in bit 7 of the surface_flag.

• The Dual Channel Algorithm (DCA) has been replaced by the Modified Dual Channel Algorithm (MDCA). MDCA achieves better retrieval performance through the modeling of polarization mixing between the vertically and horizontally polarized brightness temperature channels, as well as new estimates of single-scattering albedo and roughness coefficients. MDCA supersedes optional algorithms MPRA (option 4) and E-DCA (option 5).
• As part of the option algorithm changes, the following data fields were removed: soil_moisture_option4, vegetation_opacity_option4, retrieval_qual_flag_option4,  soil_moisture_option5, vegetation_opacity_option5, retrieval_qual_flag_option5.
• As part of the option algorithm changes, the following data fields were added: albedo_option3, roughness_coefficient_option3, bulk_density, clay_fraction.
• The baseline algorithm (SCA-V) remains unchanged.
• Improved aggregation of values in input ancillary data, e.g. roughness, soil texture, NDVI. The fix has negligible impacts on retrievals estimated to be of recommended quality.

Changes to this version include:

• Improved calibration methodology was applied to the Level-1B radiometer brightness temperatures.
• Improved land surface model outputs from the NASA Global Modeling and Assimilation Office (GMAO) were used to estimate the effective soil temperature used as input to Level-2 soil moisture geophysical inversion. This effective soil temperature is not to be confused with the physical soil temperature at a given depth (Choudhury et al., 1982).
• Improved retrieval performance of DCA (formerly known as MDCA or "the option 3" option algorithm in previous releases). DCA retrieves both soil moisture and vegetation optical depth (VOD or tau).
• Improved estimates of soil clay fraction and bulk density in most parts of the world were used in Level-2 soil moisture geophysical inversion. Work is underway to address limited spatial anomalies of these soil property estimates at high latitudes over areas rich in organic soils.
• Data quality flags were updated and corrected where faulty.
• The baseline algorithm (SCA-V) remains unchanged.

Version 1

2015-03-31 (16:28) to 2017-04-22 (23:43)

Version 1

2017-04-22 (23:39) to 2017-09-05 (23:39)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-04-24

2017-09-03 (00:16) to 2017-10-25 (23:14)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2017-09-03

2018-06-04 (13:47)

2015-03-31 (16:28) to 2018-06-14 (07:38)

Changes to this version include:

• Level-1B water-corrected brightness temperatures are used in passive soil moisture retrieval. This procedure corrects for anomalous soil moisture values seen near coastlines in the previous version and should result in less rejected data due to waterbody contamination. Five new data fields accommodate this correction: grid_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_uncorrected, and tb_v_uncorrected.
• Improved depth correction for effective soil temperature used in passive soil moisture retrieval; new results are captured in the surface_temperature data field. This correction reduces the dry bias seen when comparing SMAP data to in situ data from the core validation sites.

• Frozen ground flag updated to reflect improved freeze/thaw detection algorithm, providing better accuracy; new results are captured in bit 7 of the surface_flag.

• The Dual Channel Algorithm (DCA) has been replaced by the Modified Dual Channel Algorithm (MDCA). MDCA achieves better retrieval performance through the modeling of polarization mixing between the vertically and horizontally polarized brightness temperature channels, as well as new estimates of single-scattering albedo and roughness coefficients. MDCA supersedes optional algorithms MPRA (option 4) and E-DCA (option 5).
• As part of the option algorithm changes, the following data fields were removed: soil_moisture_option4, vegetation_opacity_option4, retrieval_qual_flag_option4,  soil_moisture_option5, vegetation_opacity_option5, retrieval_qual_flag_option5.
• As part of the option algorithm changes, the following data fields were added: albedo_option3, roughness_coefficient_option3, bulk_density, clay_fraction.
• The baseline algorithm (SCA-V) remains unchanged.
• Improved aggregation of values in input ancillary data, e.g. roughness, soil texture, NDVI. The fix has negligible impacts on retrievals estimated to be of recommended quality.

Changes to this version include:

• Improved calibration methodology was applied to the Level-1B radiometer brightness temperatures.
• Improved land surface model outputs from the NASA Global Modeling and Assimilation Office (GMAO) were used to estimate the effective soil temperature used as input to Level-2 soil moisture geophysical inversion. This effective soil temperature is not to be confused with the physical soil temperature at a given depth (Choudhury et al., 1982).
• Improved retrieval performance of DCA (formerly known as MDCA or "the option 3" option algorithm in previous releases). DCA retrieves both soil moisture and vegetation optical depth (VOD or tau).
• Improved estimates of soil clay fraction and bulk density in most parts of the world were used in Level-2 soil moisture geophysical inversion. Work is underway to address limited spatial anomalies of these soil property estimates at high latitudes over areas rich in organic soils.
• Data quality flags were updated and corrected where faulty.
• The baseline algorithm (SCA-V) remains unchanged.

This version incorporates a radar calibration update to process data for 13-23 April 2015.

• Transitioned to Validated-Stage 1
• Uses updated SPL1CS0 V3 as input
• Updates to some of the data cubes
• Update of crop database
• Modified iterative bias correction
• Estimation of VWC

2016-04-21

This version incorporates a radar calibration update to process data for 13-23 April 2015

• Transitioned to Validated-Stage 2
• Uses SPL2SMA V3 Validated and SPL2SMP V3 Validated as input
• Snapshot beta parameter estimation
• Updated soil texture files (renormalized cases where sand+clay > 100%)
• Updated default beta parameter

2016-04-21

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-03 (00:00)

Changes to this version include:

• Implemented a new method of identifying and eliminating spurious sigma0 values in Sentinel-1A/B Level-1 sigma0 data using a hybrid approach that combines a median filter with thresholding. As a result, fewer spurious sigma0 values (mainly due to small man-made structures) bias the aggregated 1 km data.
• Replaced the previous 3 km resolution urban fraction map with a new 1 km map.
• Adjusted the thresholds used with the new 1 km urban fraction map to: 0.25 (no flag), 0.25 – 0.5 (flagged, retrieval performed), and 0.5 (masked, no retrieval). These are provided in bit 3 of the surface_flag data field.
• Adjusted the tau-omega parameters to be consistent with the values used in SPL2SMP/SPL2SMP_E algorithm.
• Implemented minor bug fix to the SMAP and Sentinel-1 overlap computation code.

Changes to this version include:

• An improved calibration methodology was applied to the SMAP Level-1B brightness temperatures.
• Revised the coefficients in the land surface temperature computation to be consistent with the SMAP Level-2 soil moisture passive enhanced product. The new coefficients are C=0.246, K=1.007 for AM passes and C=1.0, K=1.007 for PM passes.
• Changed the omega parameter of the tau-omega model for forest landcover classes (1-5) from 0.05 to 0.07.
• Uses a new high-resolution soil database (Das & O'Neill, 2020).
• Uses bulk density to set the upper limit of the soil moisture retrievals. Previous versions used a fixed value of 0.65 m3/m3.
• Enhanced documentation on Data Flags in the User Guide to help data users to better understand and use the flags.
• Added a bit in the TB Disaggregation QC flag to indicate (1) the use of SMAP AM or PM data; and (2) the time difference (greater or less than 36 hours) between the SMAP and Sentinel observations overlap.
• Fixed the EASE_[row/column]_index_apm_[1km/3km] data fields to make them 0-based.
• Fixed the range beginning and ending time in the file metadata.

Changes to this version include:

• Uses updated SPL1CTB SPL2SMP V2 Beta data as input
• Corrects the retrieval quality flag error

• Transitioned to Validated-Stage 2
• Uses updated SPL2SMP V3 Validated data as input version

Changes to this version include:

• Added 6:00 p.m. ascending half orbits, which provide:
  • More frequent regional/global coverage (critical in flood monitoring)
  • Soil moisture diurnal variability information (useful in data assimilation systems)
  • Consistency with other similar satellite-based soil moisture products
• Contains frozen ground flag (bit 7 of surface_flag) derived using Normalized Polarization Ration (NPR)-based SMAP passive freeze-thaw retrieval; replaces former SMAP radar-based freeze/thaw flag

Version 4

2017-04-23 (00:00) to 2017-09-04 (00:00)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-02 (00:00) to 2017-10-25 (00:00)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2018-01-08 (00:00)

2018-06-03 (00:00)

2018-06-13 (00:00)

Changes to this version include:

• Level-1B water-corrected brightness temperatures are used in passive soil moisture retrieval. This procedure corrects for anomalous soil moisture values seen near coastlines in the previous version and should result in less rejected data due to waterbody contamination. Five new data fields accommodate this correction: grid_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_uncorrected, and tb_v_uncorrected.
• Improved depth correction for effective soil temperature used in passive soil moisture retrieval; new results are captured in the surface_temperature data field. This correction reduces the dry bias seen when comparing SMAP data to in situ data from the core validation sites.

• Frozen ground flag updated to reflect improved freeze/thaw detection algorithm, providing better accuracy; new results are captured in bit 7 of the surface_flag.

• As part of the algorithm changes, the following data fields were added: bulk_density, clay_fraction.
• The baseline algorithm (SCA-V) remains unchanged.
• Improved aggregation of values in input ancillary data, e.g. roughness, soil texture, NDVI. The fix has negligible impacts on retrievals estimated to be of recommended quality.

Changes to this version include:

• Improved calibration methodology was applied to the Level-1B radiometer brightness temperatures.
• Improved land surface model outputs from the NASA Global Modeling and Assimilation Office (GMAO) were used to estimate the effective soil temperature used as input to Level-2 soil moisture geophysical inversion. This effective soil temperature is not to be confused with the physical soil temperature at a given depth (Choudhury et al., 1982).
• Improved retrieval performance of DCA (formerly known as MDCA or "the option 3" option algorithm in previous releases). DCA retrieves both soil moisture and vegetation optical depth (VOD or tau).
• Improved estimates of soil clay fraction and bulk density in most parts of the world were used in Level-2 soil moisture geophysical inversion. Work is underway to address limited spatial anomalies of these soil property estimates at high latitudes over areas rich in organic soils.
• Added 30 new soil moisture retrieval fields associated with the two optional algorithms used in Level-2 soil moisture processing.
• Data quality flags were updated and corrected where faulty.
• The baseline algorithm (SCA-V) remains unchanged.

Version 1

2015-03-31 (00:00) to 2017-04-22 (23:59)

Version 1

2017-04-23 (00:00) to 2017-09-05 (00:00)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-03 (00:00) to 2017-10-25 (00:00)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2017-09-03

2018-01-09 (00:00) to 2018-03-13 (00:00)

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-13 (00:00)

Changes to this version include:

• Level-1B water-corrected brightness temperatures are used in passive soil moisture retrieval. This procedure corrects for anomalous soil moisture values seen near coastlines in the previous version and should result in less rejected data due to waterbody contamination. Five new data fields accommodate this correction: grid_surface_status, surface_water_fraction_mb_h, surface_water_fraction_mb_v, tb_h_uncorrected, and tb_v_uncorrected.
• Improved depth correction for effective soil temperature used in passive soil moisture retrieval; new results are captured in the surface_temperature data field. This correction reduces the dry bias seen when comparing SMAP data to in situ data from the core validation sites.

• Frozen ground flag updated to reflect improved freeze/thaw detection algorithm, providing better accuracy; new results are captured in bit 7 of the surface_flag.

Changes to this version include:

• Bug fix for the surface-uncorrected horizontally polarized brightness temperature data value, which was inadvertently assigned to the surface-uncorrected vertically polarized brightness temperature data field.
• Additional inputs from SPL2SMP_E from recovered half-orbits, which failed to process during to cold-sky maneuvers. Half-orbits were recovered using the Earth incidence angles of the footprints and by setting a threshold beyond which data are ignored.

• As part of the algorithm changes, the following data fields were added: bulk_density, clay_fraction.
• The baseline algorithm (SCA-V) remains unchanged.
• Improved aggregation of values in input ancillary data, e.g. roughness, soil texture, NDVI. The fix has negligible impacts on retrievals estimated to be of recommended quality.

Changes to this version include:

• Improved calibration methodology was applied to the SMAP Level-1B radiometer brightness temperatures.
• Improved land surface model outputs from the NASA Global Modeling and Assimilation Office (GMAO) were used to estimate the effective soil temperature used as input to Level-2 soil moisture geophysical inversion. This effective soil temperature is not to be confused with the physical soil temperature at a given depth (Choudhury et al., 1982).
• Retrieval fields associated with the two optional algorithms used in SPL2SMP processing were included in SPL3SMP.
• Data quality flags were updated and corrected where faulty.
• Improved retrieval performance of DCA (formerly known as MDCA or "the option 3" option algorithm in previous releases). DCA retrieves both soil moisture and vegetation optical depth (VOD or tau).
• Improved estimates of soil clay fraction and bulk density in most parts of the world were used in Level-2 soil moisture geophysical inversion. Work is underway to address limited spatial anomalies of these soil property estimates at high latitudes over areas rich in organic soils.
• The baseline algorithm (SCA-V) remains unchanged.

This version incorporates a radar calibration update to process data for 13-23 April 2015.

• Transitioned to Validated-Stage 1
• Uses SPL2SMA V3 Validated data as input; inherited all changes and improvements of the new version

This version incorporates a radar calibration update to process data for 13-23 April 2015.

• Transitioned to Validated-Stage 2
• Using SPL2SMAP V3 Validated data as input

2016-04-21

This version incorporates a radar calibration update to process data for 13-23 April 2015.

2015-07-07 (00:00)

• Transitioned to Validated-Stage 2
• Uses SPL1CS0 V3 Validated data as input
• Using full swath except for nadir-anomaly flagged areas to provide better coverage
• Resolved some flag and fillValue errors

2017-04-22 (23:59)

2017-04-23 (00:00) to 2017-09-05 (00:00)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-06 (00:00) to 2017-10-25 (00:00)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2018-01-09 (00:00) to 2018-03-13 (00:00)

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

2018-06-03 (00:00)

Changes to this version include:

• Implementation of a supplementary single-channel V-pol (SCV) algorithm for areas of lower latitudes where the seasonal difference of the NPR algorithm is too small to be effectively used to discriminate freeze/thaw state; results are captured in the retrieval_quality_flag. This change provides stronger flag agreement between Tair and Tsoil, and for ascending/p.m. versus descending/a.m. overpasses due to physics (e.g. the NPR algorithm response to wet snow over frozen soil in spring). It also addresses an artifact of the validation approach (e.g. soils remain thawed for weeks after freeze onset in fall due to insulation from snow).
• With the addition of the new SCV algorithm to the NPR baseline algorithm, spatial coverage of freeze/thaw data was extended to global. Data are output on a fixed global 36 km EASE-Grid 2.0 and are provided in the Freeze_Thaw_Retrieval_Data_Global group.
• Updated retrieval_quality_flag for water contamination/permanent ice.
• Implementation of false flag mitigation using TB screening and AMSR-E weekly climatology maps, resulting in significantly fewer false flags.

No science change. CRID incremented to coincide with updates to L1-L3 radiometer products. In addition, /Metadata/GridSpatialRepresentation and /Metadata/Extent structures modified to include definitions for both Polar and Global grid metadata parameters.

No science change. CRID incremented to coincide with the release of SPL2SMP V6, SPL2SMP_E V3, SPL3SMP V6, and SPL3SMP_E V3.

Changes to this version include:

• Adjusted the freeze/thaw reference states for the normalized polarization ratio (NPR) algorithm per the improved Level-1 brightness temperature recalibration. The freezing reference averages from 2016-2020 and the thaw reference averages from 2015-2019.
• Adjusted the reference states for the Single-Channel V (SCV) algorithm per the update of the GEOS-FP surface and soil temperature profiles.
• Improved the never frozen/never thawed masks for false-flag mitigation by:
  • extending the temporal extent of the AMSR-E source data to include data through 2019
  • blending in a GEOS-FP temperature climatology for 2015-2020 using a loose ±10 ºC criterion for fully-frozen or fully-thawed conditions.
• The product data structure, content, and processor code are otherwise unchanged from the previous version.

Validated-Stage 3 (Report)

2017-09-05 (00:00)

• Processing capabilities for the upcoming SMAP/Sentinel-1 radiometer/radar soil moisture product
• SPL1BTB processing change to Atmospheric Correction to ensure proper unit conversion
• Changes to resolve bugs that were causing SPL1BTB_E processing to fail
• Note: Temporal coverage for CRID R15060 varies slightly; though the majority of R15060 files begin at 2017-04-24 (11:00), some R15060 files appear earlier in the time series. 

2017-09-06 (00:00) to 2017-10-25 (00:00)

• Updated compiler optimization flag in radiometer processor to reduce run time
• Compiled optimization flags
• Bug fix for initialization error (error surfaced by optimization flags)
• Note that the data content/quality has not changed

2018-01-09 (00:00) to 2018-03-13 (00:00)

No science change. CRID incremented to coincide with an update to the radiometer reflector ancillary file for January and February 2018.

Changes to this version include:

• Implementation of a supplementary single-channel V-pol (SCV) algorithm for areas of lower latitudes where the seasonal difference of the NPR algorithm is too small to be effectively used to discriminate freeze/thaw state; results are captured in the retrieval_quality_flag. This change provides stronger flag agreement between Tair and Tsoil, and for ascending/p.m. versus descending/a.m. overpasses due to physics (e.g. the NPR algorithm response to wet snow over frozen soil in spring). It also addresses an artifact of the validation approach (e.g. soils remain thawed for weeks after freeze onset in fall due to insulation from snow).
• With the addition of the new SCV algorithm to the NPR baseline algorithm, spatial coverage of freeze/thaw data was extended to global. Data are output on a fixed global 36 km EASE-Grid 2.0 and are provided in the Freeze_Thaw_Retrieval_Data_Global group.
• Updated retrieval_quality_flag for water contamination/permanent ice.
• Implementation of false flag mitigation using TB screening and AMSR-E weekly climatology maps, resulting in significantly fewer false flags.

No science change. CRID incremented to coincide with the release of SPL2SMP V6, SPL2SMP_E V3, SPL3SMP V6, and SPL3SMP_E V3.

Changes to this version include:

• Adjusted the freeze/thaw reference states for the normalized polarization ratio (NPR) algorithm per the improved Level-1 brightness temperature recalibration. The freezing reference averages from 2016-2020 and the thaw reference averages from 2015-2019.
• Adjusted the reference states for the Single-Channel V (SCV) algorithm per the update of the GEOS-FP surface and soil temperature profiles.
• Improved the never frozen/never thawed masks for false-flag mitigation by:
  • extending the temporal extent of the AMSR-E source data to include data through 2019
  • blending in a GEOS-FP temperature climatology for 2015-2020 using a loose ±10 ºC criterion for fully-frozen or fully-thawed conditions.
• The product data structure, content, and processor code are otherwise unchanged from the previous version.

Version 1

SPL4SMAU
SPL4SMGP
SPL4SMLM

Version 1 

SPL4SMAU
SPL4SMGP
SPL4SMLM

Input data source changed from SPL1CTB V1 Beta data to SPL1CTB V2 Validated-Stage 1 data.

Version 2 

SPL4SMAU
SPL4SMGP
SPL4SMLM

• Transitioned to Validated-Stage 2
• Using updated SPL1CTB V3 Validated data as input
• Minor bug fixes

Vv2010

Version 2  

SPL4SMAU
SPL4SMGP
SPL4SMLM

Version 3

SPL4SMAU
SPL4SMGP
SPL4SMLM

2018-06-04 (01:30)

Changes to this version include:

• SMAP observations are now assimilated in Eastern Europe, the Middle East, and East Asia due to expanded coverage of the brightness temperature scaling parameters. The latter are based on two years of SMAP Version 3 brightness temperature observations where the SMOS climatology is unavailable due to RFI.
• An improved version of the model-only Nature Run (NRv4.1) simulation is used to derive the brightness temperature scaling parameters, the model soil moisture initial conditions, and the soil moisture climatology.
• Minor bug fixes.

Version 4

SPL4SMAU
SPL4SMGP
SPL4SMLM

Changes to this version include:

• The land surface modeling system was revised in the following ways:
  • Improved input parameter data sets for land cover, topography, and vegetation height are based on more recent data sets. Land cover inputs were updated to the GlobCover2009 product, resulting in a slightly different land mask between Version 3 and Version 4. Topographic statistics now rely on observations from the Shuttle Radar Topography Mission. Finally, vegetation height inputs are derived from space-borne lidar measurements.
  • The model background precipitation forcing is rescaled to match the climatology of the Global Precipitation Climatology Project (v2.2), which results in substantial changes in the precipitation and soil moisture climatology in Africa and the high latitudes, where the gauge-based Climate Prediction Center Unified precipitation is not used.
  • SMAP Level-2 soil moisture retrievals and in situ soil moisture measurements from the Soil Climate Analysis Network and U.S. Climate Reference Network were used to calibrate a particular Catchment model parameter that governs the recharge of soil moisture from the model’s root-zone excess reservoir into the surface excess reservoir. Specifically, the replenishment of soil moisture near the surface from below under non-equilibrium conditions was substantially reduced, which brings the model’s surface soil moisture more in line with the SMAP Level-2 and in situ soil moisture.
  • Additional model changes include revisions to the parameters and parameterizations of the surface energy balance and the snow depletion curve.
• The Version 4 brightness temperature scaling parameters are based on eight years of SMOS observations and three years of SMAP observations where the SMOS climatology is unavailable due to radio frequency interference. Note that the calibration of the assimilated SMAP brightness temperatures changed substantially from Version 3 to Version 4.
• Analysis increments are no longer computed for the “catchment deficit” model prognostic variable in the Ensemble Kalman filter update step.
• Minor bug fixes.
• Added x and y coordinate variables [including arrays of EASE-Grid 2.0 coordinate values, Climate and Forecast (CF)-compliant metadata, and HDF-5 dimension scales] as well as an EASE-Grid 2.0 projection grid mapping variable. This augmentation of L4 soil moisture data files improves interoperability and user workflow via ArcGIS/QGIS, OPeNDAP, and programmatic access. Three new data fields accommodate this change: EASE2_global_projection, x, and y. 

Version 4

SPL4SMAU
SPL4SMGP
SPL4SMLM

Version 4

SPL4SMAU
SPL4SMGP
SPL4SMLM

Continued as forward-processing stream from 2018-06-05 (01:30). 

Version 5

SPL4SMAU
SPL4SMGP
SPL4SMLM

Version 5

SPL4SMAU
SPL4SMGP
SPL4SMLM

Forward-processing data using published Version 5 (“R17”) Radiometer Brightness Temperatures (SPL1CTB) as input.  Otherwise, seamless continuation of Vv5012.

Changes to this and Vv5012 include:

• The Level-4 soil moisture algorithm was recalibrated to work with the substantially changed calibration of the assimilated Level-1C brightness temperatures.
• The brightness temperature scaling parameters in the updated Level-4 soil moisture algorithm are based on five years of SMAP observations (April 2015 – March 2020).
• The land surface modeling system underpinning the updated Level-4 soil moisture algorithm was revised in the following ways:
  • Improved surface aerodynamic roughness length (z0) formulation, including use of a stem area index.
  • Corrected an error in the fitting procedure used for one of the topography-related functions in the Catchment model, which potentially affected the simulation of soil moisture in about 2% of all land surface elements (De Lannoy et al. 2014).
  • Updated calibration of the microwave radiative transfer model parameters. 
• The updated Level-4 soil moisture algorithm includes major software upgrades, including full compliance with the Earth System Modeling Framework, a modular and extensible software design approach, for improved support of future science development. 
• Minor bug fixes.

Version 5

SPL4SMAU
SPL4SMGP
SPL4SMLM

Reprocessed data from 2015-03-31 using published Version 5 ("R17") Radiometer Brightness Temperatures (SPL1CTB) as input. 

Changes to this version include:

• Additional minor updates to the calibration of the microwave radiative transfer model parameters for improved coverage and consistency.

Changes to this version include:

• Transitioned to Validated-Stage 2
• Using SPL4SMAU V2 Validated and SPL4SMGP V2 Validated data as input
• Update to process radiometer data from 2015-03-31 to 2015-04-12
• Some data fields renamed from *_av to *_mean
• Updated to have have continuous RMSE-based "quality" fields instead of the categorical quality flag in V1

2018-06-04 (00:00)

Changes to this version include:

• Uses dynamic 8-day fPAR inputs obtained from the latest (Collection 6) MODIS fPAR record at 500 m resolution. The preprocessor was updated to handle the finer resolution MODIS Collection 6 inputs, which are interpolated to 1 km resolution prior to model processing. The prior (Version 2) processor used MODIS Collection 5 fPAR inputs, which were derived at 1 km resolution.
• Updated the ancillary MODIS fPAR 8-day climatology used for fPAR gap-filling as an L4C model preprocessing step to reflect new MODIS Collection 6 fPAR inputs. The fPAR climatology is derived from a longer 14-year (2000-2014) MODIS record relative to the original 12-year (2000-2012) Collection 5 fPAR record used in Version 2 processing.
• For each grid cell, a sine-curve-based seasonal fPAR climatology curve is now used to identify and screen anomalous 8-day fPAR variations in the preprocessor. This change reduces impacts of anomalous fPAR temporal variations that may not be captured by the MODIS fPAR product quality control (QC) flags, particularly during seasonal transitions at northern latitudes.
• Updated and recalibrated the ancillary Biome Properties Look-Up Table (BPLUT) and re-initialized the model initial global soil organic carbon (SOC) pools to reflect new MODIS Collection 6 fPAR inputs. The BPLUT calibration was conducted using global historical FLUXNET in situ tower eddy covariance CO2 flux measurement records for representative global land cover types using a similar step-wise calibration procedure employed for the Version 2 product.
• A minor bug fix to the post-processor was made to ensure that all grid cell no-data fill values are identified with a consistent -9999 notation; the prior Version 2 product erroneously assigned some no-data values as -999900.

Changes to this version largely affect model inputs and ancillary files rather than changes to the internal model structure or code. Note that Version 4 is slightly better than Version 3 in RMSE terms, with improvement generally larger for drier sites. Specific changes include:

• The carbon model biome properties lookup table (BPLUT) has been calibrated using an augmented FLUXNET global tower site record which includes more calibration sites (335 sites compared to 228 sites for V3), expanded tower data records extending to at least 2015, and the addition of new tower sites representing more land cover types.
• Revised Level-4 carbon global model calibration and SOC initialization using an extended (2000-2017) MODIS fPAR (V006) record and the latest SMAP Nature Run (NRv7.2) climate data records.
• Implemented minor changes to spatial weighting of calibration tower sites within a model grid cell and reduced the outlier influence on model response curve fitting.

Reprocessed data from 2015-03-31 using Version 4 (Vv4030) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP) as input.

Continued as forward-processing stream from 2018-06-05 (01:30)

Changes to this version include:

• Reprocessed data from 2015-03-31 using Version 4 (Vv4030) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP) as input.
• Added x and y coordinate variables [including arrays of EASE-Grid 2.0 coordinate values, Climate and Forecast (CF)-compliant metadata, and HDF-5 dimension scales] as well as an EASE-Grid 2.0 projection grid mapping variable. This augmentation of L4 carbon data files improves interoperability and user workflow via ArcGIS/QGIS, OPeNDAP, and programmatic access. Three new data fields accommodate this change: EASE2_global_projection, x, and y. 

2020-08-27 (00:00) to 2021-04-24 (00:00)

Forward-processing data using published Version 5 (Vv5014) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP) as input. Otherwise, seamless continuation of Vv5022.

Changes to this version primarily represent changes to the model inputs and model Biome Properties Look-up Table (BPLUT) calibration rather than changes to the internal model structure or code. The Version 5 product accuracy and performance is largely consistent with Version 4. Specific changes include:

• Revised Level-4 carbon global model calibration and soil organic carbon (SOC) initialization using the latest SMAP Nature Run (NRv8.3) soil moisture and soil temperature data, and MERRA-2 surface meteorology.
• The carbon model BPLUT has been recalibrated using a FLUXNET2015 global tower site record that includes 329 sites representing all major global plant functional type (PFT) classes.
• Implemented minor changes to spatial weighting of FLUXNET2015 tower sites in the Level-4 carbon model BPLUT calibration. Northern (≥ 45°N) tower sites now have greater impact in defining global PFT response characteristics; whereby, the adjusted weighting is designed to enhance product performance in boreal-arctic biomes. It also incorporated a more detailed set of PFT realistic range constraints for the BPLUT parameters prior to the model calibration and optimization.
• Enhanced an attribute in the legend_carbon_model_bitflag data field to include descriptions of the bit values.

Version 5

2015-03-31 (00:00) to present

Reprocessed data from 2015-03-31 using published Version 5 (Vv5030) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP) as input.

Changes to this version include:

• Improved spin-up initial condition for soil organic initial carbon content.

Validated - Stage 3

Vv5040

2020-01-06