Dust Optical Centroid Height (AOCH) over bright surface: first retrieval from TROPOMI oxygen A and B absorption bands

Abstract

The vertical distribution of dust layers can influence dust transport, radiative forcing, deposition and ultimately, surface particulate matter mass concentration. Although many dust layer height (ALH) products from passive satellite measurements have been developed, most of them are applicable on dark surfaces only. Here, building on the absorbing aerosol optical centroid height (AOCH) retrieval from hyperspectral O₂ A and B absorption band measurements of TROPOspheric Monitoring Instrument (TROPOMI) for dark target, we further develop dust AOCH retrieval over bright surfaces. Key updates include: 1) the thresholds in cloud mask tests are refined with consideration of the different spectral characteristics of bright surface reflectance; and 2) the assumption of Lambertian surface is modified to the Ross-Li Bidirectional Reflectance Distribution Function (BRDF) model to consider the angular dependence of surface reflectance. The validation against the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) for several dust plumes over Saharan Desert illustrates that TROPOMI AOCH has ~1 km uncertainty and ~0.1 km mean bias, better than ~1 km underestimated dust layer mean altitude (ALT) from the Infrared Atmospheric Sounder Interferometer (IASI). With this implement of bright surfaces, our algorithm is ready for global retrieval and will be applicable for similar hyperspectral instrument in the future.