Remote sensing of the ocean surface refractive index

Abstract:

Although the refractive index is widely regarded as the main proxy for chemical composition, its direct measurement in remote sensing contexts has so far eluded experimenters, and field measurements remain extremely scarce. Inversions of airborne Research Scanning Polarimeter (RSP) observations in the short-wave infrared (SWIR) collected within the sunglint region, where the degree of linear polarization (DoLP) is determined by the fundamental Fresnel laws of specular reflection, were demonstrated to yield measurements of the ocean surface refractive index with surprising accuracy.

With suitable polarimeters finally scheduled for launch onboard the PACE mission, we discuss the corrections needed to apply the same method to the HARP-2 and SPEXone observational wavelengths, significantly more affected by atmospheric scattering than the RSP 2264 nm channel. To this end, we perform advanced inversions of simulated PACE DoLP data using the 870 nm wavelength under a range of conditions, analyzing their information content via a rigorous assessment of the uncertainties. The goal is to promote the ``ocean surface refractive index'' (for every HARP2 pixel within the sunglint region) to be a novel product useful for investigations on processes involving the ocean surface, and for the detection of oil spills and other contaminants. An added benefit is the recovery of pixels otherwise discarded from PACE imagery as “sunglint-contaminated”, which will be turned into a useful resource for oceanographic and climate studies.