PhD Proposal: Greema Regmi
Location
Physics : 401
Date & Time
August 26, 2024, 9:00 am – 12:00 pm
Description
ADVISOR: Dr. J. Vanderlei Martins
TITLE: Development of Advanced Retrieval Approaches in GRASP Using the LiDARs and Multi-Angle Polarimeters (MAPs)
ABSTRACT: Accurate retrievals of aerosol geophysical variables are crucial to better constrain climate change projection estimates and formulate effective policies for a sustainable future. The accuracy of the retrieved microphysical and optical properties relies on the assumptions and methods adopted in the retrieval algorithms. LiDAR and Multi-Angular Polarimetric measurements are highly complementary and offer an attractive opportunity for synergistic retrievals. Column-effective radiometric and polarimetric intensities from Multi-Angular Polarimeters (MAPs) paired with vertically resolved backscattering, extinction and depolarization at high spatial resolution from LiDARs, can significantly increase the available information content in an observed scene. We will perform combined LiDAR+MAP retrievals on dust scenes observed from the Research Scanning Polarimeter (RSP) and the Second generation High Spectral Resolution Lidar (HSRL-2) instruments during various NASA aircraft campaigns like ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES). The retrievals will employ the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm coupled with non-spherical optical property databases of spheroid and hexahedral particles from the TAMUdust2020database. We will compare the effects of these shape assumptions on forward modeling and the retrieved properties across different sensor setups: HSRL-2-only, RSP-only, and the combined HSRL-2+RSP. Preliminary findings suggest that incorrect assumptions about aerosol morphology primarily influence the retrieval of single scattering albedo and size distribution, with a lesser impact on aerosol optical depth (AOD). Additionally, we found that the spheroid model tends to underestimate the depolarization of pure dust in the combined RSP+HSRL-2 retrievals. In contrast, the hexahedral shape model with a sphericity degree of 0.7 reproduced the depolarization closer to the measurement.
Since dust particle morphology depends on the dust source and its transport distance, we will assess the sensitivity of retrieved microphysics to varying the model's degree of sphericity. Additionally, we will develop a scheme to provide appropriate a priori information where necessary. By testing and comparing multiple methods, we aim to create a robust retrieval scheme that enhances GRASP's accuracy in reproducing measurements and ensures more consistent retrievals. This work is crucial for developing algorithms for future missions like NASA's Atmosphere Observing System (AOS), which aims to use an advanced polarimeter alongside an advanced LiDAR.
TITLE: Development of Advanced Retrieval Approaches in GRASP Using the LiDARs and Multi-Angle Polarimeters (MAPs)
ABSTRACT: Accurate retrievals of aerosol geophysical variables are crucial to better constrain climate change projection estimates and formulate effective policies for a sustainable future. The accuracy of the retrieved microphysical and optical properties relies on the assumptions and methods adopted in the retrieval algorithms. LiDAR and Multi-Angular Polarimetric measurements are highly complementary and offer an attractive opportunity for synergistic retrievals. Column-effective radiometric and polarimetric intensities from Multi-Angular Polarimeters (MAPs) paired with vertically resolved backscattering, extinction and depolarization at high spatial resolution from LiDARs, can significantly increase the available information content in an observed scene. We will perform combined LiDAR+MAP retrievals on dust scenes observed from the Research Scanning Polarimeter (RSP) and the Second generation High Spectral Resolution Lidar (HSRL-2) instruments during various NASA aircraft campaigns like ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES). The retrievals will employ the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm coupled with non-spherical optical property databases of spheroid and hexahedral particles from the TAMUdust2020database. We will compare the effects of these shape assumptions on forward modeling and the retrieved properties across different sensor setups: HSRL-2-only, RSP-only, and the combined HSRL-2+RSP. Preliminary findings suggest that incorrect assumptions about aerosol morphology primarily influence the retrieval of single scattering albedo and size distribution, with a lesser impact on aerosol optical depth (AOD). Additionally, we found that the spheroid model tends to underestimate the depolarization of pure dust in the combined RSP+HSRL-2 retrievals. In contrast, the hexahedral shape model with a sphericity degree of 0.7 reproduced the depolarization closer to the measurement.
Since dust particle morphology depends on the dust source and its transport distance, we will assess the sensitivity of retrieved microphysics to varying the model's degree of sphericity. Additionally, we will develop a scheme to provide appropriate a priori information where necessary. By testing and comparing multiple methods, we aim to create a robust retrieval scheme that enhances GRASP's accuracy in reproducing measurements and ensures more consistent retrievals. This work is crucial for developing algorithms for future missions like NASA's Atmosphere Observing System (AOS), which aims to use an advanced polarimeter alongside an advanced LiDAR.
