Investigation of the challenges associated with the practical application of atmospheric tomography with 3D radiative transfer
Lundstrom, John T
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https://hdl.handle.net/2142/125724
Description
Title
Investigation of the challenges associated with the practical application of atmospheric tomography with 3D radiative transfer
Author(s)
Lundstrom, John T
Issue Date
2024-07-15
Director of Research (if dissertation) or Advisor (if thesis)
Di Girolamo, Larry
Department of Study
Climate Meteorology & Atm Sci
Discipline
Atmospheric Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Tomography
3D Radiative Transfer
Cloud/Aerosol Microphysics
Abstract
Frequent, global observations of cloud optical and microphysical properties distributed in 3D space are much sought after in a multitude of fields such as cloud physics, climate modeling, and numerical weather prediction. Current satellite remote sensing retrievals provide global and frequent observations of cloud optical depth and effective radius of the drop size distribution; however, the use of 1D radiative transfer rather than 3D radiative transfer in the interpretation of radiances leads to retrieval biases in optical depth and effective radius that depend on cloud regime and sun-view geometry. Moreover, retrieved quantities such as cloud droplet effective radius lack information of the in-cloud vertical structure of microphysics, which is highly desired for advancements in fields such as cloud physics. Tomography, which uses images from multiple view angles to reconstruct the 3D structure of cloud and aerosol optical and microphysical properties, is a new paradigm in passive remote sensing which is emerging to replace the traditional approaches that use 1D radiative transfer.
Recent developments in Atmospheric Tomography with 3D Radiative Transfer (AT3D) eliminate the bias caused by using 1D radiative transfer and retrieves the highly desired 3D distribution of cloud and aerosol microphysical and optical properties through multi-view angle observations. Previous investigations point toward the success of AT3D in cases where the traditional 1D radiative transfer approach suffers from greatest error such as in small heterogeneous clouds, although work thus far has been largely done in highly idealized synthetic environments. I demonstrate the practical application of AT3D to retrieve the 3D distribution of cloud volume extinction coefficient using observations from the Multi-angle Imaging SpectroRadiometer (MISR) that were coincident with the Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex). Comparison of retrieved volume extinction coefficient against in situ observations from microphysics probes aboard the NASA P-3 aircraft during CAMP2Ex are presented as a form of validation; retrieved values of extinction coefficient fall within the range of CAMP2Ex observations. However, there are several practical limitations when applying AT3D to real observations. One such limitation is from the imposition of radiative horizontal boundary conditions, and we explore this by characterizing retrieval error with respect to domain size through a set of simulations using synthetic cloud fields. We find that retrieval error within the center portion of the retrieval domain decreases as domain size increases. We also find the spatial extent to which errors penetrate the retrieval domain depend on the embedded cloud regime with the most significant errors occurring within 2 km of the domain boundary. These results suggest that errors due to the violation of horizontal boundary conditions are present with any practical application of the tomographic technique. This research will aid in the definition of requirements, such as satellite swath width, for future earth observing missions targeting clouds and aerosols.
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