Polarimetric remote sensing in oxygen A and B bands: sensitivity study and information content analysis for vertical profile of aerosols

Theoretical analysis is conducted to reveal the information content of aerosol vertical profile in space-borne measurements of the backscattered radiance and degree of linear polarization (DOLP) in oxygen (O-2) A and B bands. Assuming a quasi-Gaussian shape for aerosol vertical profile characterized by peak height H and half width gamma (at half maximum), the Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is used to simulate the Stokes four-vector elements of upwelling radiation at the top of atmosphere (TOA) and their Jacobians with respect to H and gamma. Calculations for different aerosol types and different combinations of H and gamma values show that the wide range of gas absorption optical depth in O-2 A and B band enables the sensitivity of backscattered DOLP and radiance at TOA to the aerosol layer at different altitudes. Quantitatively, DOLP in O-2 A and B bands is found to be more sensitive to H and gamma than radiance, especially over the bright surfaces (with large visible reflectance). In many O-2 absorption wavelengths, the degree of freedom of signal (DFS) for retrieving H (or gamma) generally increases with H (and gamma) and can be close to unity in many cases, assuming that the composite uncertainty from surface and aerosol scattering properties as well as measurements is less than 5 %. Further analysis demonstrates that DFS needed for simultaneous retrieval of H and gamma can be obtained from a combined use of DOLP measurements at similar to 10-100 O-2 A and B absorption wavelengths (or channels), depending on the specific values of H. The higher the aerosol layer, the fewer number of channels for DOLP measurements in O-2 A and B bands are needed for characterizing H and gamma. Future hyperspectral measurements of DOLP in O-2 A and B bands are needed to continue studying their potential and their combination with radiance and DOLP in atmospheric window channels for retrieving the vertical profiles of aerosols, especially highly scattering aerosols, over land.