Copernicus Imaging Microwave Radiometer (CIMR) Benefits for the Copernicus Level 4 Sea-Surface Salinity Processing Chain

Daniele Ciani,Gian Luigi Liberti,Rosalia Santoleri,Craig Donlon,Catherine Prigent,Bruno Buongiorno Nardelli

doi:10.3390/rs11151818

Abstract

We present a study on the potential of the Copernicus Imaging Microwave Radiometer (CIMR) mission for the global monitoring of Sea-Surface Salinity (SSS) using Level-4 (gap-free) analysis processing. Space-based SSS are currently provided by the Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) satellites. However, there are no planned missions to guarantee continuity in the remote SSS measurements for the near future. The CIMR mission is in a preparatory phase with an expected launch in 2026. CIMR is focused on the provision of global coverage, high resolution sea-surface temperature (SST), SSS and sea-ice concentration observations. In this paper, we evaluate the mission impact within the Copernicus Marine Environment Monitoring Service (CMEMS) SSS processing chain. The CMEMS SSS operational products are based on a combination of in situ and satellite (SMOS) SSS and high-resolution SST information through a multivariate optimal interpolation. We demonstrate the potential of CIMR within the CMEMS SSS operational production after the SMOS era. For this purpose, we implemented an Observing System Simulation Experiment (OSSE) based on the CMEMS MERCATOR global operational model. The MERCATOR SSSs were used to generate synthetic in situ and CIMR SSS and, at the same time, they provided a reference gap-free SSS field. Using the optimal interpolation algorithm, we demonstrated that the combined use of in situ and CIMR observations improves the global SSS retrieval compared to a processing where only in situ observations are ingested. The improvements are observed in the 60% and 70% of the global ocean surface for the reconstruction of the SSS and of the SSS spatial gradients, respectively. Moreover, the study highlights the CIMR-based salinity patterns are more accurate both in the open ocean and in coastal areas. We conclude that CIMR can guarantee continuity for accurate monitoring of the ocean surface salinity from space.

Highlights

The salinity of the ocean is a crucial parameter to investigate the water cycle, the ocean dynamics and the marine biogeochemistry from the global to the regional scale
We focused on the year 2016 that is compatible with the other datasets used in this study
Checking different sea-surface salinity (SSS)-sea-surface temperature (SST)-Ocean Wind Speed (OWS)-Total Cloud Liquid Water (TCLW)-Total Cloud Water Vapour (TCWV) combinations, we found that the local low SST and high OWS are primarily responsible for the σSSS increase, consistently with [19]

Summary

Introduction

The salinity of the ocean is a crucial parameter to investigate the water cycle, the ocean dynamics and the marine biogeochemistry from the global to the regional scale It was classified as an Essential Climate Variable in the context of the Global Climate Observing System (GCOS) programme. Salinity affects both the sea water density and the marine carbonate chemistry (alkalinity), making it a fundamental variable to investigate the thermohaline global circulation, the local surface and deep circulation, the water mass transformation and the uptake of carbon by the ocean including ocean acidification, e.g., [1,2,3,4]. The characterization of the sea-surface salinity (SSS) has benefited from satellite observations and on their synergy with in situ measurements, e.g., [7,8,9]

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Conclusion