Abstract
Precise knowledge about aerosols in the lower atmosphere (optical properties and vertical distribution) is particularly important for studying the Earth’s climatic and weather conditions. Measurements from satellite sensors in sun-synchronous and geostationary orbits can be used to map distributions of aerosol parameters in global or regional scales. The new-generation sensor Tropospheric Monitoring Instrument (TROPOMI) onboard the Copernicus Sentinel-5 Precursor (S5P) measures a wide variety of atmospheric trace gases and aerosols that are associated with climate change and air quality using a number of spectral bands between the ultraviolet and the shortwave infrared. In this study, we perform a sensitivity analysis of the forward model parameters and instrument information that are associated with the retrieval accuracy of aerosol layer height (ALH) and optical depth (AOD) using the oxygen (O2) A-band. Retrieval of aerosol parameters from hyperspectral satellite measurements requires accurate surface representation and parameterization of aerosol microphysical properties and precise radiative transfer calculations. Most potential error sources arising from satellite retrievals of aerosol parameters, including uncertainties in aerosol models, surface properties, solar/satellite viewing geometry, and wavelength shift, are analyzed. The impact of surface albedo accuracy on retrieval results can be dramatic when surface albedo values are close to the critical surface albedo. An application to the real measurements of two scenes indicates that the retrieval works reasonably in terms of retrieved quantities and fit residuals.
Highlights
Estimating aerosol optical properties and vertical distribution appears to be a challenging task because of real-time variations in aerosol microphysical properties
The retrieval results of aerosol layer height (ALH) and AOD for the two selected Tropospheric Monitoring Instrument (TROPOMI) scenes are plotted in Figures 11, 12, respectively, which seem to capture the spatial patterns seen from Figure 10 under different aerosol loading scenarios
We have developed an aerosol retrieval algorithm for estimating aerosol parameters (ALH and AOD) from the O2 A-band of TROPOMI
Summary
Estimating aerosol optical properties and vertical distribution appears to be a challenging task because of real-time variations in aerosol microphysical properties. Deriving aerosol information from satellite measurements remains a critical challenge in terms of retrieval sensitivity and accuracy This is in general an underdetermined task and often requires several assumptions to be made with respect to the properties of aerosol and surface (Kokhanovsky and Rozanov, 2010). We extend the sensitivity analysis by taking into account more inputs during the inversion, i.e., different models for aerosol microphysical parameterization, surface properties, solar/viewing geometry, and wavelength shift. These inputs and information are considered to likely affect the retrieval accuracy and this sensitivity analysis aims to quantify the impact and importance of each input.
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