Preparing the potential and challenge of remote sensing-based sea surface salinity estimation: the CoSMOS airborne campaign

Abstract

Measurement of ocean surface salinity dynamics from space poses numerous engineering and scientific challenges that push the boundaries of ocean remote sensing capabilities. The principles of measuring sea surface salinity (SSS) from space are well established. They involve precise determination of the dielectric characteristics of seawater through lownoise passive microwave (MW) radiometer measurement of the ocean's brightness temperature (TB), optimally performed at a low frequency near 1.4 GHz (L-band). Sea surface salinity from space clearly presents new challenges because science requirements impose the need for resolution of the order of 0.1 psu (practical salinity units). This requirement means that competing terms carried in the ocean TB measurements, foremost being sea surface temperature (SST) and ocean surface roughness, must be accounted for in a new and more robust manner. To reach this aim, we developed consistent forward electromagnetic/geophysical models for the expected surface roughness and foam emissivity signatures [1] at L-band. We also provided models to correct for sunglint [2] and galactic radiation [3] scattered towards the future SMOS sensor. Finally, we have defined the Auxiliary data processing for SMOS, including the processing to get the key SST and wind fields needed for the salinity retrieval [4]. Prior to launch, airborne field measurement efforts are currently on going to perform algorithm validation exercises. Here, we present results from the ESA airborne Campaign CoSMOS, performed in the North Sea in April 2006. This campaign was conducted to help to clarify and bound the limits of uncertainty for the geophysical factors affecting sea surface emissivity at L-band, in order to develop successful salinity inversion algorithms.