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Description

The SMAP-SSS level 2C near real-time (NRT) V5.0 dataset produced by the Remote Sensing Systems (RSS) and sponsored by the NASA Ocean Salinity Science Team, is a validated product that provides near real-time orbital/swath data on sea surface salinity (SSS) derived from the NASA's Soil Moisture Active Passive (SMAP) mission. SMAP, launched on January 31, 2015, was initially designed to measure and map Earth's soil moisture and freeze/thaw state to better understand terrestrial water, carbon and energy cycles, and has been adapted to measure ocean SSS and ocean wind speed using its passive microwave instrument. The SMAP instrument is in a near polar orbiting, sun synchronous orbit with a nominal 8 day repeat cycle.

The dataset includes derived SMAP SSS, SSS uncertainty using the NRT SMAP Salinity Retrieval Algorithm, top of atmosphere brightness temperature (TB), wind speed and direction data for extreme winds, and other all necessary ancillary data and the results of all intermediate steps. Data from July 28, 2022 to present, is available with a latency of about 6 hours. The observations are global, provided on a 0.25° fixed Earth grid with an approximate spatial resolution of 70 km. The major differences to the standard version 5.0 data products are: (1) the NRT version of the L1B SMAP antenna temperatures is used, (2) the latest 6-hourly 0.25° wind speed and direction are used for the ancillary wind speed and direction input, (3) the CMC SST from 2 days earlier is used for the ancillary SST input, (4) the sea-ice mask of the 3-day aggregate RSS AMSR-2 Air-Sea Essential Climate Variables (AS-ECV) data set from 2-days earlier is used for the sea-ice flag, (5) no correction for sea-ice contamination is performed, it is recommended to use only SMAP data that are classified to be within sea-ice zone 0 for open ocean scene and no sea-ice contamination.

This RSS SMAP-SSS V5.0 NRT dataset holds tremendous potential for scientific research and various applications. Given the SMAP satellite's near-polar orbit and sun-synchronous nature with its 1000km swath, it achieves global coverage in approximately three days, enabling researchers to monitor and model global oceanic and climatic phenomena with unprecedented detail and timeliness. These data can inform and enhance understanding of global weather patterns, the Earth’s hydrological cycle, ocean circulation, and climate change.
This activity was informed by the Satellite Needs Working Group (SNWG), an interagency effort of the U.S. Government dedicated to identifying and addressing Earth observation needs across U.S. civilian federal agencies.

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
2022-07-28
Data Partner
Physical Oceanography Distributed Active Archive Center, Jet Propulsion Laboratory, NASA (NASA/JPL/PODAAC)
Concept ID
C2646960543-POCLOUD
Data State
ACTIVE
Number of Files/Granules
17359
Processing Level
2
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. (2023). RSS SMAP Level 2C Sea Surface Salinity NRT V5.0 Validated Dataset [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/SMP50-2SNRT Date Accessed: 2026-04-10

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
alpha Scan angle: +90 is left of forward. +270 is right of forward. degree float -9999 0 to 360 1 N/A
anc_sea_ice_flag ancillary sea-ice detection indicator 1 byte 0 N/A 1 N/A
cellat Latitude of OI Earth grid cell degrees_north float -9999 -90 to 90 1 N/A
cellon Longitude of OI Earth grid cell degrees_east float -9999 0 to 360 1 N/A
dtb_land_correction TA land correction applied at TOA. Pol basis V,H Kelvin float -9999 N/A 1 N/A
dtemp_ant Empirical correction to physical temperature of reflector. Pol basis V,H Kelvin float -9999 N/A 1 N/A
eaa Azimuthal look angle relative to North degree float -9999 0 to 360 1 N/A
eia Earth incidence angle degree float -9999 0 to 90 1 N/A
fland land fraction within footprint 1 float -9999 0 to 1 1 N/A
gallat Latitudinal (polar) angle of specular reflection ray in ECI2000 degree float -9999 -90 to 90 1 N/A
gallon Longitudinal (azimuthal) angle of specular reflection ray in ECI2000 degree float -9999 0 to 360 1 N/A
gland land fraction weighted by antenna gain 1 float -9999 0 to 1 1 N/A
iqc_flag 32-bit quality control flag 1 int 1 N/A 1 N/A
monglt Moon glint angle degree float -9999 -180 to 180 1 N/A
pra Polarization basis rotation angle (geometric part) degree float -9999 -90 to 90 1 N/A
pratot_exp Expected total polarization basis rotation angle: Faraday rotation (from external TEC) + geometric degree float -9999 -90 to 90 1 N/A
rain rain rate. estimated from NCEP could water profiles mm h-1 float -9999 0 to 25 1 N/A
sea_ice_zones sea-ice contamination zones 1 byte 7 0 to 6 1 N/A
solar_flux Ancillary solar flux (from NOAA SWPC) 1e-22 W m-2 Hz-1 float -9999 N/A 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_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
sunglt Sun glint angle. Negative value means that sun ray pierces the Earth. degree float -9999 -180 to 180 1 N/A
sun_alpha Sun azimuth angle in S/C coordinate system degree float -9999 0 to 360 1 N/A
sun_beta Sun zenith angle in S/C coordinate system degree float -9999 0 to 180 1 N/A
surtep Ancillary sea surface temperature (from CMC) Kelvin float -9999 0 to 313.15 1 N/A
ta_ant unfiltered antenna temperature. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
ta_ant_calibrated Antenna temperature after correcting for emissive reflector and TND adjustment. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
ta_ant_exp Expected (RTM) antenna temperature before any losses. This is to be compared with ta_ant_calibrated. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
ta_ant_filtered RFI filtered antenna temperature. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
ta_earth Antenna temperature after correcting for cold space, galaxy, sun, moon. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
ta_gal_dir TA of direct galaxy intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1 N/A
ta_gal_ref TA of reflected galaxy intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1 N/A
ta_sun_dir TA of direct sun intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1 N/A
ta_sun_ref TA of reflected sun intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1 N/A
tbdw Atmospheric downwelling brightness temperature Kelvin float -9999 N/A 1 N/A
tbup Atmospheric upwelling brightness temperature Kelvin float -9999 N/A 1 N/A
tb_consistency sqrt(chi2) of MLE in SSS retrieval Kelvin float -9999 N/A 1 N/A
tb_sur Brightness temperature at rough ocean surface BEFORE applying roughness correction. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_sur0 Brightness temperature at flat ocean surface AFTER applying roughness correction. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_sur0_exp Expected (RTM) at flat ocean surface. SIC added. This is to be compared with tb_sur0, before SIC. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_sur0_sic Brightness temperature at flat ocean surface after applying roughness correction and sea-ice correction. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_toa Brightness temperature at top of atmosphere BEFORE applying land correction. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_toa_lc Brightness temperature at top of atmosphere AFTER applying land correction. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
tb_toi Brightness temperature at top of ionosphere. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1 N/A
TEC Vertically integrated electron content between surface and S/C 1e16 m-2 float -9999 N/A 1 N/A
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