1. Validating SMAP SSS with in situ measurements
Wenqing Tang1, Alexander Fore1, Simon Yueh1,
Tong Lee1, Akiko Hayashi1,
Alejandra Sanchez-Franks2, Justino Martinez3,
Brian King2, and Dariusz Baranowski1
1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
2National Oceanography Centre, Southampton, UK
3Institut de Ciències del Mar, CSIC, Barcelona, Spain

2. SMAP observes global monthly salinity fields consistent with Aquarius, SMOS and Argo OI
May 2015
SMAP
Aquarius
SMOS
Argo (SIO)
JPL SMAP TB-only SSS retrieval (V3.0) [Fore et al., 2016] April 2015 – present, available at
ftp://sealion.jpl.nasa.gov/pub/outgoing/smap/v3.0, or ourcoean.jpl.nasa.gov

3. Comparison of SMAP L3 data with Argo OI products (monthly, top 5m)
SMAP SSS retrieved from L-band radiometer has achieved an accuracy of 0.2 PSU globally between 40S and 40N on a monthly basis

4. Comparison with tropical moored buoy arrays (daily, 1m)
0°N, 90°E
SMAP salinity has very good skill to track large scale salinity changes on weekly time scales. Correlation > 0.6 in 77 out of 97 buoy locations

5. Possible malfunction of buoy salinity sensor and the corrupted real time data that is not flagged
5°N, 95°W

6. 2°S, 125°W

7. Subsurface buoy salinity (10m, 20m) is in agreement with SMAP

8. 18-months mean (April 2015 – Sept. 2016)
Comparison with ship-based thermosalinograph (TSG) data in the Mediterranean Sea
SMAP
TSG
SMAP-TSG
18-months mean (April 2015 – Sept. 2016)
TSG data are daily averaged on a 0.25 grid then matched up with SMAP daily L3
Averaged over 18 months, the collocated pairs of SMAP and ship data have correlation of 0.78 with a bias of 0.12 PSU and a standard deviation of 0.51 PSU and RMSD of 0.52 PSU
Caveat: Since no trajectory adjusted TSG data available for the time period of interest, the in situ salinity map was produced using non-adjusted data which may carry large biases.
For example, anomalously high salinity is measured by the TSG just south of the Ebro mouth and an apposite situation occurs close to Cyprus Island.
Ship-based TSG data from:
The Global Ocean Surface Underway Data (GOSUD) Project ( and
the Copernicus marine database (

9. Comparison with individual Argo float (< 10 m) data in the Mediterranean Sea

10. Comparison with Argo STS floats (< 1 m) in the Bay of Bengal
The daily STS data are matched up with the closest SMAP L3 grid point and plotted over the weekly SMAP SSS data, which is produced from SMAP L2 data for the same time period.
Also shown is the near surface ocean currents from OSCAR (Ocean Surface Current Analysis Real-time, available from
Both SMAP and the Argo STS floats depict a salty water intrusion from the Arabian Sea into the BOB during the Indian Summer Monsoon.
During the Bay of Bengal Boundary Layer Experiment (BoBBLE) project field campaign (June-July 2016), 7 Argo floats were deployed in the southern Bay of Bengal (BOB). Of particular interest to this study is the daily near surface salinity measurements from the BoBBLE floats equipped with SeaBird (SBE) 41-CP CTD sensor and Surface Temperature Salinity (STS) sensors which return very high-resolution salinity profiles with continuous sampling at a rate of 1Hz, which results in a resolution of ~10cm in the surface 20 dbar.

11. Conclusions
SMAP SSS retrieved from L-band radiometer has achieved an accuracy of 0.2 PSU globally between 40S and 40N on a monthly basis comparing with Argo OI products
salinity measured at 1 m by moored buoys indicate SMAP is able to track large salinity changes that occured within one month, with RMSD of 0.26 PSU on weekly time scales and 0.22 PSU on monthly time scales. Our analysis also suggests that the satellite SSS has the potential to be used for real-time QC of mooring salinity data to detect measurements that are significantly affected by issues such as biofouling.
In the Mediterranean Sea, the spatial pattern of SSS from SMAP is confirmed by the ship-based TSG. Comparison with individual Argo floats suggests the SMAP retrieval algorithm performs better in the Western Mediterranean region, but suffers from radio-frequency interference (RFI) and land contamination in the Eastern Mediterranean region and Adriatic Sea.
Comparison with the Argo float STS from the BoBBLE field campaign show SMAP observed the sub-monthly evolution of the Arabian Sea high salinity intrusion into the BOB.