Simultaneous Aerosol and Ocean Properties From the PolCube CubeSat Polarimeter

Abstract

We quantify the performance of aerosol and ocean remote sensing products from the PolCube instrument using a previously developed polarimeter retrieval algorithm based on optimal estimation. PolCube is a modified version of the PolCam lunar instrument on the Korea Pathfinder Lunar Orbiter that has been optimized for Earth-Science observations of aerosol, ocean, and thin cloud optical properties. The objective of the PolCube instrument is to retrieve detailed fine-mode (pollution and smoke) and coarse-mode (sea-salt and dust) aerosol properties over the ocean for a range of light to heavy aerosol loadings using its polarimetric-imaging capability at multiple angles and wavelengths from 410−865 nm. An additional objective is to discriminate aerosols from thin clouds. PolCube’s retrieval performance of aerosol optical and microphysical properties and ocean products is quantitatively assessed. We estimate that PolCube can retrieve total aerosol optical depth at 555 nm (AOD555) within ±0.068, fine-mode AOD555 within ±0.078, and fine-mode single-scattering albedo within ±0.036, where all uncertainties are expressed as one standard deviation (1σ). PolCube’s accurate and high-resolution aerosol-retrieval products will provide unique spatial and temporal coverage of the Earth that can be used synergistically with other instruments, such as the Geostationary Environmental Monitoring Spectrometer to improve air-quality forecasting.

The PACE-MAPP algorithm: Simultaneous aerosol and ocean polarimeter products using coupled atmosphere-ocean vector radiative transfer

“…We assume that all measurements are independent, whereas the actual instrument measurements are expected to be correlated. This error model has been used previously and appears to work well in forecasting the realworld performance of the RSP instrument together with retrievals performed on synthetic data generated by Monte-Carlo-style sampling of the aerosol and ocean parameters (Pena and Pal, 2009;Stamnes et al, 2018b;Stamnes et al, 2021). An investigation of the impact of measurement correlations on retrieval performance may be undertaken once the measurement correlations of the instruments are determined.…”

“…The single-scattering properties of spherical particles are obtained using the highly accurate and freely available Scale Invariance Rule Aerosol Look-Up Table (SIR-A LUT) (Chemyakin et al, 2021). The single-scattering properties of the spheroidal dust particles are computed using the AERONET LUT (Dubovik et al, 2006).…”

Circular polarization in atmospheric aerosols

“…In contrast, several investigations on the chiral nature of commonly found atmospheric aerosols have become available in the last decade. For example, naturally formed secondary organic aerosols (SOAs) have a distinct chiral structure in the Amazon forests (Ebben et al, 2011;Martinez et al, 2011) and in maritime pine forests (Staudt et al, 2019). The fact that aerosol gaseous precursors are chiral is important because the chirality of the gas remains when it forms or attaches to an aerosol as shown by Ebben et al (2012).…”

“…Its low range has been a challenging requirement for Earth-observing sensors that have exposure times of the order of milliseconds as opposed to planetary probes that had much coarser spatial resolutions and longer exposure times. Sensor sensitivity and lack of a compelling scientific application have been the main reasons to justify the lack of inclusion of CP observation in spectro-polarimeters to be deployed in the near future (Craven-Jones et al, 2014;Dubovik et al, 2019;Stamnes et al, 2021;Trippe, 2014). Interestingly this fact was already raised by Kemp et al (1971) who noted that the "the appreciable linear polarization of the planets .…”