Polarimetric Sensitivity of Light-Absorbing Carbonaceous Aerosols Over Ocean: A Theoretical Assessment

TL;DR

This paper provides a theoretical assessment of how light-absorbing carbonaceous aerosols affect radiance and polarization signals at the top of the atmosphere, aiding remote sensing retrievals over ocean surfaces.

Contribution

It introduces a detailed theoretical analysis of polarimetric signals related to different types of carbonaceous aerosols across multiple wavelengths and particle sizes, using advanced scattering models.

Findings

Degree of linear polarization (DoLP) is closely related to phase matrix elements at 470 nm.

Weakly absorbing aerosols are more sensitive to particle size and refractive index changes.

Black carbon shows less variation in polarimetric signals compared to brown carbon.

Abstract

Visible-light-absorbing carbonaceous aerosols within the boundary layer affect the radiance and polarization states of the radiation at the top of the atmosphere. Remote sensing from suborbital and satellite-based platforms utilizes these radiance and polarization signals to retrieve the key properties of these aerosols. Recent retrieval algorithms have shown a progressive trend toward including multi-angular and multi-spectral polarimetric measurements to produce better retrieval accuracy in comparison to those using measurements based on a single viewing angle. Here, we perform a theoretical investigation of the top of atmosphere (TOA) radiance-related reflectance factor (bidirectional reflectance factor (BRF)) and the two types of polarimetry-related factors (polarized bidirectional reflectance factor (pBRF) and the degree of linear polarization (DoLP)) for different types of atmospheric light-absorbing carbonaceous aerosols as a function of particle size distribution. We selected three polarimetric bands corresponding to those utilized by NASA Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) -- near-UV (470 nm), visible (660 nm), and near-infrared (865 nm) -- for our simulations which were performed over ocean surface using the successive order of scattering (SOS) algorithm coupled to a Lorenz-Mie aerosol optics model. The analysis of particle phase matrix elements indicates a close relationship between the angular dependencies of DoLP and associated phase matrix components at the shortest polarimetric band (470 nm). Using Jacobian analysis, we find that the radiance- and polarimetry-related reflectance factors of weakly light-absorbing aerosols, such as brown carbon, are more sensitive to changes in particle size and imaginary refractive index in comparison with those of black carbon, which is strongly light-absorbing.