On the Use of Space-based Polarimetric Measurements for Ocean Colour Remote Sensing – Heritage and Perspective

The polarization of the light within the water body has been already documented, and very well described from in-situ measurements. This signature mostly results from the process of scattering by all the constituents of the water body, the molecular water itself, but also hydrosols, including phytoplankton and non-algal particles, as well as water surface reflection and refraction. Mie scattering calculations demonstrated the sensitivity of Polarization with the chemical and physical properties of marine particles (nature and quantity of particle, refractive index, size, shape...). As roughly for the scalar radiance, the marine polarised radiance once propagated to the topof-atmosphere layer remains small and contributes to less than 10-20% of the total polarized radiance depending on the water types, aerosols and wavelengths. Observation of the polarization from space have been experienced based on POLDER sensors. While for open ocean, the atmospheric correction or the accuracy of the estimation of the surface wind speed could be improved, it was possible to retrieve a significant water leaving polarized reflectance for bright waters. Alternatively, a new approach proposes to analyse the parallel polarized contribution with respect to the observing meridian plane, which reduces significantly the perturbing contribution from surface reflection. Despite these past studies, the potential of polarization from spaced-borne measurements remains largely un-exploited for ocean colour purposes. The 3MI mission, a POLDER follow-on improved instrument on-board EPS-SG, will offer beyond 2021 the opportunity for a long-term time series acquisition in fully operational framework. Applications to marine analysis will be therefore possible. Other polarimetric information could also be available from SGLI/GCOM-C, OCI/PACE or