Remote sensing of aerosol properties over the ocean using near-infrared and shortwave infrared multiangular polarimetry: information content analysis

Polarimetry helps to improve the characterization of the microphysical properties of atmospheric aerosol. This paper investigates the importance of the spectral range, the spectral band, the number of viewing angles, and the polarimetric accuracy for aerosol retrieval from polarization measurements over the ocean. For this purpose, we simulate a series of single-viewing-angle and multiple-viewing-angle polarimetric observation scenarios in the near-infrared (NIR) and shortwave infrared (SWIR) bands for two different levels of aerosol loading and two types of maritime aerosols derived from the Aerosol Robotic Network (AERONET) measurements. The results indicate that the total aerosol degrees of freedom for signal (DFS) can be increased by at least 1.02 with the addition of SWIR intensity and polarization measurements in the single-angle observation mode. This improvement corresponds to the retrieval of one to two additional aerosol parameters. In the multi-viewing experiment, the columnar volume concentration, effective radius, and complex refractive index for both fine and coarse size modes benefit from additional viewing angles. Furthermore, incorporating additional multi-angle SWIR measurements can enhance the total aerosol DFS by approximately 1.1-3.3, as this approach can better capture the angular structure exhibited by the scattering matrix of coarse aerosols. The analysis also indicates that the polarimetric accuracy has a significant impact on the uncertainty of aerosol retrieval. The results of this study provide an important reference for the design of future polarimetric instruments and the development of retrieval algorithms.