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Description

The version 5.0 SMAP-SSS level 3, monthly gridded product is based on the fourth release of the validated standard mapped sea surface salinity (SSS) data from the NASA Soil Moisture Active Passive (SMAP) observatory, produced operationally by Remote Sensing Systems (RSS) with a one-month latency. The major changes in Version 5.0 from Version 4 are: (1) the addition of formal uncertainty estimates to all salinity retrieval products. (2) Sea-ice flagging and sea-ice side-lobe correction based on direct ingestion of AMSR-2 brightness temperature (TB) measurements. This is in contrast to Version 4 and earlier versions in which the sea-ice correction was based on an external sea-ice concentration product. The use of AMSR-2 TB measurements in the SMAP Version 5 products allows for salinity retrievals closer to the sea-ice edge and aids in the detection of large icebergs near the Antarctic. Monthly data files for this product are averages over one-month time intervals. SMAP data begins on April 1,2015 and is ongoing, with a one-month latency in processing and availability. L3 products are global in extent with a default spatial resolution of approximately 70KM. The datasets are gridded at 0.25degree x 0.25degree. Note that while a SSS 40KM variable is also included in the product, for most open ocean applications, the default SSS variable (70KM) is best used as they are significantly less noisy than the 40KM data. The SMAP satellite is in a near-polar orbit at an inclination of 98 degrees and an altitude of 685 km. It has an ascending node time of 6 pm and is sun-synchronous. With its 1000km swath, SMAP achieves global coverage in approximately 3 days, but has an exact orbit repeat cycle of 8 days. On board instruments include a highly sensitive L-band radiometer operating at 1.41GHz and an L-band 1.26GHz radar sensor providing complementary active and passive sensing capabilities. Malfunction of the SMAP scatterometer on 7 July, 2015, has necessitated the use of collocated wind speed, primarily from WindSat, for the surface roughness correction required for the surface salinity retrieval.

Product Summary

Platforms
SMAP
Instruments
SMAP L-BAND RADIOMETER
Spatial Extent

N: 90 S: -90 E: 180 W: -180

Spatial Resolution
0.25 Decimal Degrees x 0.25 Decimal Degrees
Location
GLOBAL
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2015-04-01
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C2208416221-POCLOUD
Data State
ACTIVE
Number of Files/Granules
104
Processing Level
3
Published
Updated
Science Keywords
Salinity

Citation

Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.

Copy Citation

Remote Sensing Systems. (2022). RSS SMAP Level 3 Sea Surface Salinity Standard Mapped Image Monthly V5.0 Validated Dataset [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/SMP50-3SMCS Date Accessed: 2026-04-17

Documents

Variables

The table below lists the variables contained within a single granule for this dataset. Variables often contain observed or derived geophysical measurements collected from a variety of sources, including remote sensing instruments on satellite and airborne platforms, field campaigns, in situ measurements, and model outputs. The terms variable, parameter, scientific data set, layer, and band have been used across NASA’s Earth science disciplines; however, variable is the designated nomenclature in NASA’s Common Metadata Repository (CMR). Variable metadata attributes such as Name, Description, Units, Data Type, Fill Value, Valid Range, and Scale Factor allow users to efficiently process and analyze the data. The full range of attributes may not be applicable to all variables. Additional information on variable attributes is typically available in the data, user guide, and/or other product documentation.

For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor Offset
fland average land fraction within 3dB contour 1 float -9999 0 to 1 1 N/A
gice_est estimated sea ice fraction weighted by antenna gain 1 float -9999 0 to 1 1 N/A
gland average land fraction weighted by antenna gain 1 float -9999 0 to 1 1 N/A
lat center latitude of grid cell degrees_north float N/A -90 to 90 1 N/A
lon center longitude of grid cell degrees_east float N/A 0 to 360 1 N/A
nobs Number of observations for L3 average of SSS smoothed to approx 70km resolution 1 int 0 1 to 480 1 N/A
nobs_40km Number of observations for L3 average of SSS at 40km resolution 1 int 0 1 to 480 1 N/A
nobs_RF Number of observations for L3 average of rain filtered SSS smoothed to approx 70km resolution 1 int 0 1 to 480 1 N/A
sss_ref Reference sea surface salinity from HYCOM 1e-3 float -9999 0 to 45 1 N/A
sss_smap SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_40km SMAP sea surface salinity at original 40km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_40km_unc total formal uncertainty estimate of SMAP sea surface salinity at original 40km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_40km_unc_comp formal uncertainty components of SMAP sea surface salinity at original 40km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_RF Rain filtered SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_RF_unc total formal uncertainty estimate of rain filtered SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_unc total formal uncertainty estimate of SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1 N/A
sss_smap_unc_comp formal uncertainty components of SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1 N/A
surtep Ancillary sea surface temperature (from CMC) Kelvin float -9999 0 to 313.15 1 N/A
time reference time of analyzed variable field corresponding to center of the product time interval seconds since 2000-01-01T00:00:00Z double N/A N/A 1 N/A
winspd Ancillary sea surface wind speed from CCMP NRT that is used in surface roughness correction m s-1 float -9999 0 to 100 1 N/A
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