Aerosol Layer Height Over Water from O2 A-band: Mono-Angle Hyperspectral and/or Bi-spectral Multi-Angle Observations

Success of NASA’s Phytoplankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission 1 depends critically on atmospheric correction to retrieve inherent properties of oceanic waters. 2 Previously unexplored UV wavelengths are the most challenging to correct due to large signals 3 from Rayleigh and aerosol scattering. The dominant Rayleigh component makes it difficult to 4 separate absorption by aerosols or by hydrosols and/or dissolved chemicals. Knowing the height 5 of the aerosol layer greatly helps to break this degeneracy because it controls the Rayleigh portion, 6 but this information has to come from elsewhere. Fortunately, PACE’s imaging spectrometer, Ocean 7 Color Instrument (OCI) covers the oxygen A-band. We adopt a simple analytical radiative transfer 8 (RT) model in order to gain physical insights and to quantify the information content (IC) of OCI 9 spectroscopy. We also use the RT model to determine the IC of a notional multi-angle sensor, for 10 instance, as planned for the Multi-Angle Imager for Aerosols (MAIA) mission, with a bi-spectral take 11 on the A-band, in-band and continuum channels. Finally, to investigate synergies between the two 12 approaches, we quantify their combined IC. Both sensors should enable height retrieval but neither, 13 even combined, has enough IC to infer aerosol layer thickness. 14