Remote sensing of sea surface salinity: challenges and research directions

Young Jun Kima Department of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea

Daehyeon Hana Department of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea

Eunna Jangb Korea Ocean Satellite Center, Korea Institute of Ocean Science and Technology, Busan, South Korea

Jungho Ima Department of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan, South KoreaCorrespondence[email protected]

https://orcid.org/0000-0002-4506-6877

Taejun Sunga Department of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea

ABSTRACT

Salinity is a key parameter that affects the surface, deep circulations, and heat transport of oceans. Sea surface salinity (SSS) represents the salinity at the ocean surface and impacts atmosphere – ocean interactions and vertical ocean circulation. To monitor SSS, three passive microwave radiometers with an L-band (1.4 GHz) have been launched since 2009. The scientific need for SSS retrieval and estimation has grown in recent years; however, the operational retrieval of SSS via satellite remote sensing still faces significant challenges. This study provides a review of satellite-based SSS retrieval methods and guidelines to encourage future research. This paper introduces satellite-derived SSS research trends and summarizes the representative SSS satellite sensors and their retrieval methods. The limitations and challenges of satellite-derived SSS are then discussed. The errors from the retrieval algorithms, discrepancies in the spatio-temporal scales of in situ and remote sensing, and limitations of the satellite-derived SSS are then detailed. Finally, our paper provides suggestions for the future directions of SSS remote sensing in five ways: mitigation of measurement errors, improvement of currently available SSS products, enhancement of the usage of in situ data, reconstruction of three-dimensional salinity information, and synergetic uses of multi-satellite missions.

KEYWORDS:

Acknowledgements

This research was supported by “Technology development for Practical Applications of Multi-Satellite data to maritime issues (20180456)”, “Development of Advanced Science and Technology for Marine Environmental Impact Assessment (20210427)”, and “Development of technology using analysis of ocean satellite images (20210046)” of Korea Institute of Marine Science & Technology promotion (KIMST) funded by the Ministry of Oceans and Fisheries, South Korea.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The raw data used in this study are publicly available from the sources provided in following links. The processed data and codes generated from this study are available upon request to the corresponding author.

- ARGO in situ data: https://argo.ucsd.edu/data/

- Aquarius L2 data: https://podaac.jpl.nasa.gov/dataset/AQUARIUS_L2_SSS_CAP_V5

- SMOS L2 data: https://smos-diss.eo.esa.int/oads/access/collection

- SMAP L2 data: https://podaac.jpl.nasa.gov/dataset/SMAP_JPL_L2B_SSS_CAP_V5

- SMAP L3 data: https://podaac.jpl.nasa.gov/dataset/SMAP_JPL_L3_SSS_CAP_8DAY-RUNNINGMEAN_V5