A multispectral polarimetric instrument concept based on metasurface filters

Remote sensing of aerosols requires spectropolarimetric information over different viewing angles with demanding polarimetric accuracy and growing interest for smaller designs. In this paper, we investigate an instrument design that implements a metasurface filter which enables both functions simultaneously, allowing further miniaturization and integrability. The instrument offers 1 km ground sampling distance over its entire field of view, in Low Earth Orbit, and the concept makes use of 6 modules to cover the wide field of view requested for aerosol retrieval with a total of 7 radiation-resistant lenses. This choice enables an optical volume per module under 50mm x 50mm x 150mm and smaller relative angles of incidence. The filters are designed to cover 6 spectral bands from 443nm to 870nm with a spectral resolution of 2-5nm. The wide spectral band is achieved by using 3 distributed Bragg reflectors with bandpass filters, integrated in one double-cavity structure that can be glued on a CCD/CMOS sensor. The two cavities, operating as a metasurface, contain scatterers of different dimensions enabling the fine-tuning of the spectral resonance and the polarization filtering. Multiscale forward modeling techniques are employed for the estimation of the polarimetric accuracy with optical aberrations and realistic coatings. Using radiance values from the PACE mission, polarimetric errors and SNR at each pixel are estimated and compared to requirements of state-of-the-art missions.