Abstract
A radiative transfer simulator was developed to compute the synthetic data of all three instruments onboard NASA’s Plankton Aerosol, Cloud, ocean Ecosystem (PACE) observatory, and at the top of the atmosphere (TOA). The instrument suite includes the ocean color instrument (OCI), the Hyper-Angular Rainbow Polarimeter 2 (HARP2), and the Spectro-Polarimeter for Planetary Exploration 1 (SPEXone). The PACE simulator is wrapped around a monochromatic radiative transfer model based on the successive order of scattering (RTSOS), which accounts for atmosphere and ocean coupling, polarization, and gas absorption. Inelastic scattering, including Raman scattering from pure ocean water, fluorescence due to chlorophyll, and colored dissolved organic matter (CDOM), is also simulated. This PACE simulator can be used to explore the sensitivity of the hyperspectral and polarized reflectance of the Earth system with tunable atmosphere and ocean parameters, which include aerosol and cloud number concentration, refractive indices, and size distribution, ocean particle microphysical parameters, and solar and sensor-viewing geometry. The PACE simulator is used to study two important case studies. One is the impact of the significant uncertainty in pure ocean water absorption coefficient to the radiance field in the ultraviolet (UV) spectral region, which can be as much as 6%. The other is the influence of different amounts of brown carbon aerosols and CDOM on the polarized radiance field at TOA. The percentage variation of the radiance field due to CDOM is mostly for wavelengths smaller than 600 nm, while brown aerosols affect the whole spectrum from 350 to 890 nm, primarily due to covaried soot aerosols. Both case studies are important for aerosol and ocean color remote sensing and have not been previously reported in the literature.
Highlights
NASA’s Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission will carry the Ocean Color Instrument (OCI), which is a hyperspectral scanning radiometer with spectral coverage from the ultraviolet (340 nm) to near-infrared (890 nm) measured at 5 nm spectral resolution with 2.5-nm spectral sampling (Werdell et al, 2019)
We report a PACE simulator, which can simulate the hyperspectral radiance that ocean color instrument (OCI) would measure and the polarized signals at multiple wavelengths and multiple viewing angles from Hyper-Angular Rainbow Polarimeter 2 (HARP2) and SPEXone
In the second sensitivity study, we check the influences of different amounts of brown carbon aerosols in the atmosphere and colored dissolved organic matter (CDOM) in the ocean to the TOA polarized reflectance to explore how one can address the difficulty of separating the two signals
Summary
Peng-Wang Zhai 1*, Meng Gao 2,3, Bryan A. Inelastic scattering, including Raman scattering from pure ocean water, fluorescence due to chlorophyll, and colored dissolved organic matter (CDOM), is simulated This PACE simulator can be used to explore the sensitivity of the hyperspectral and polarized reflectance of the Earth system with tunable atmosphere and ocean parameters, which include aerosol and cloud number concentration, refractive indices, and size distribution, ocean particle microphysical parameters, and solar and sensor-viewing geometry. The percentage variation of the radiance field due to CDOM is mostly for wavelengths smaller than 600 nm, while brown aerosols affect the whole spectrum from 350 to 890 nm, primarily due to covaried soot aerosols Both case studies are important for aerosol and ocean color remote sensing and have not been previously reported in the literature
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