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Description

The RSS SMAP level 2C sea surface salinity V6.0 dataset produced by the Remote Sensing Systems (RSS) and sponsored by the NASA Ocean Salinity Science Team, is a validated product that provides orbital/swath data on sea surface salinity (SSS) derived from the NASA's Soil Moisture Active Passive (SMAP) mission. The SMAP satellite was launched on 31 January 2015
with 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. 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.
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The major changes in Version 6.0 from Version 5.0 are: (1) Removal of biases during the first few months of the SMAP mission that are related to the operation of the SMAP radar during that time. (2) Mitigation of biases that depend on the SMAP look angle. (3) Mitigation of salty biases at high Northern latitudes. (4) Revised sun-glint flag.
The SMAP-SSS L2C product includes data for a range of parameters: derived sea surface salinity (SSS) with SSS-uncertainty, brightness temperatures for each radiometer polarization, antenna temperatures, collocated wind speed, data and ancillary reference surface salinity data from HYCOM, rain rate, quality flags, and navigation data.
Each data file covers one 98-minute orbit (15 files per day), is available in netCDF-4 file format with about 4 days l
atency.
Data begins on April 1,2015 and is ongoing. Observations are global in extent with an approximate spatial resolution of 40KM. Note that while a SSS 40KM variable is also included in the product for most open ocean applications, The standard product of the SMAP Version 6.0 release is the smoothed salinity product with a spatial resolution of approximately 70 km.

Product Summary

Platforms
SMAP
Instruments
SMAP L-BAND RADIOMETER
Spatial Extent

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

Spatial Resolution
47000 Meters x 39000 Meters
Geographic Region
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
C2832221740-POCLOUD
Data State
ACTIVE
Number of Files/Granules
46037
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. (2024). RSS SMAP Level 2C Sea Surface Salinity V6.0 Validated Dataset [Data set]. NASA Physical Oceanography Distributed Active Archive Center. https://doi.org/10.5067/SMP60-2SOCS Date Accessed: 2025-12-14

Documents

Variables

Variables are a set of physical properties whose values determine the characteristics or behavior of something. For example, temperature and pressure are variables of the atmosphere. Parameters and variables can be used interchangeably. Variable level attributes provide individual information for each variable.

The Name in this table is the variable name. Fill value indicates missing or undefined data points in a variable. Valid range is the range of values the variable can store. Scale factor is used to increase or decrease the size of an object and can be used to correct for distortion. For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor
alpha Scan angle: +90 is left of forward. +270 is right of forward. degree float -9999 0 to 360 1
anc_sea_ice_flag ancillary sea-ice detection indicator 1 byte 0 N/A 1
cellat Latitude of OI Earth grid cell degrees_north float -9999 -90 to 90 1
cellon Longitude of OI Earth grid cell degrees_east float -9999 0 to 360 1
dtb_land_correction TA land correction applied at TOA. Pol basis V,H Kelvin float -9999 N/A 1
dtb_sea_ice_correction TB sea-ice correction applied at TB SUR 0. Pol basis V,H Kelvin float -9999 N/A 1
dtemp_ant Empirical correction to physical temperature of reflector. Pol basis V,H Kelvin float -9999 N/A 1
eaa Azimuthal look angle relative to North degree float -9999 0 to 360 1
eia Earth incidence angle degree float -9999 0 to 90 1
fland land fraction within footprint 1 float -9999 0 to 1 1
gallat Latitudinal (polar) angle of specular reflection ray in ECI2000 degree float -9999 -90 to 90 1
gallon Longitudinal (azimuthal) angle of specular reflection ray in ECI2000 degree float -9999 0 to 360 1
gice_est estimated sea ice fraction weighted by antenna gain 1 float -9999 0 to 1 1
gland land fraction weighted by antenna gain 1 float -9999 0 to 1 1
iqc_flag 32-bit quality control flag 1 int 1 N/A 1
monglt Moon glint angle degree float -9999 -180 to 180 1
pra Polarization basis rotation angle (geometric part) degree float -9999 -90 to 90 1
pratot_exp Expected total polarization basis rotation angle: Faraday rotation (from external TEC) + geometric degree float -9999 -90 to 90 1
rain IMERG rain rate. Resampled to SMAP resolution. mm h-1 float -9999 0 to 25 1
sea_ice_zones sea-ice contamination zones 1 byte 7 0 to 6 1
solar_flux Ancillary solar flux (from NOAA SWPC) 1e-22 W m-2 Hz-1 float -9999 N/A 1
sss_ref Reference sea surface salinity from HYCOM 1e-3 float -9999 0 to 45 1
sss_smap SMAP sea surface salinity smoothed to approx 70km resolution 1e-3 float -9999 0 to 45 1
sss_smap_40km SMAP sea surface salinity at original 40km resolution 1e-3 float -9999 0 to 45 1
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
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
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
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
sunglt Sun glint angle. Negative value means that sun ray pierces the Earth. degree float -9999 -180 to 180 1
sun_alpha Sun azimuth angle in S/C coordinate system degree float -9999 0 to 360 1
sun_beta Sun zenith angle in S/C coordinate system degree float -9999 0 to 180 1
surtep Ancillary sea surface temperature (from CMC) Kelvin float -9999 0 to 313.15 1
ta_ant unfiltered antenna temperature. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1
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
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
ta_ant_filtered RFI filtered antenna temperature. Pol basis V,H,S3,S4 Kelvin float -9999 0 to 330 1
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
ta_gal_dir TA of direct galaxy intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1
ta_gal_ref TA of reflected galaxy intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1
ta_sun_dir TA of direct sun intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1
ta_sun_ref TA of reflected sun intrusion. Pol basis I,Q,S3 Kelvin float -9999 N/A 1
tbdw Atmospheric downwelling brightness temperature Kelvin float -9999 N/A 1
tbup Atmospheric upwelling brightness temperature Kelvin float -9999 N/A 1
tb_consistency sqrt(chi2) of MLE in SSS retrieval Kelvin float -9999 N/A 1
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
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
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
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
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
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
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