The JPL SMAP Sea Surface Salinity Retrieval Algorithm
[27-Aug-2018] Fore, A., Yueh, S., Tang, W., and Hayashi, A.
Presented at the 2018 Ocean Salinity Science Team and Salinity Continuity Processing Meeting
The Soil Moisture Active Passive (SMAP) mission was launched January 31st, 2015. It is designed to measure the soil moisture over land using a combined active / passive L-band system. Due to the Aquarius mission, L-band model functions for ocean winds and salinity are already mature and have been directly applied to the SMAP mission. In contrast to Aquarius, the higher resolution and scanning geometry of SMAP allows for wide-swath ocean winds and salinities to be retrieved. In this talk we present the SMAP Sea Surface Salinity (SSS) dataset and algorithm.
We begin with a discussion of the lineage of the SMAP SSS algorithms and model functions from Aquarius, showing excellent agreement for the ocean surface roughness correction. Next we discuss positives and negatives of a conically-scanning radiometer such as SMAP as compared to a push-broom platform like Aquarius. Then, we give an overview of some newly developed algorithms that are only relevant to the SMAP system, such as a new galaxy correction and a land correction enabling SMAP SSS retrievals to be done up to 40 km from coast, which have been implemented in the JPL version 3 SSS algorithm. The JPL SMAP SSS data, validated with in situ
ARGO, tropical moorings, and ship-based observations, are available from the JPL Physical Oceanography Distributed Active Archive Center (PO.DAAC).
Version 4 of the JPL SMAP SSS data product contains a number of recent algorithm improvements. We have implemented and validated an expected SSS uncertainty estimate for each L2B retrieval and L3 SSS retrieval. This will aid efforts to optimally blend SMAP SSS with other SSS such as from SMOS. We have modified the ancillary numerical weather products used in the SSS algorithm and have significantly improved performance in high-wind conditions. Other changes include an extended range of SSS retrievals up to 45 PSU, retrievals in land-locked inland lakes, improved land correction, and reduction of biases at high latitudes.
Finally we discuss the various L2B and L3 datasets available from SMAP and where they may be obtained.