Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data

The Research Scanning Polarimeter (RSP) is an airborne along-track scanner measuring the polarized and total reflectances in 9 spectral channels. The RSP was a prototype for the Aerosol Polarimetery Sensor (APS) launched on-board the NASA Glory satellite. Currently the retrieval algorithms developed...

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Autores principales:	Mikhail D. Alexandrov, Claudia Emde, Bastiaan Van Diedenhoven, Brian Cairns
Formato:	article
Lenguaje:	EN
Publicado:	Frontiers Media S.A. 2021
Materias:	clouds tomography radon transform research scanning polarimeter reflectance airborne remote sensing Geophysics. Cosmic physics QC801-809 Meteorology. Climatology QC851-999
Acceso en línea:	https://doaj.org/article/ee801c76b25c4b1ca757109be21af27e
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spelling	oai:doaj.org-article:ee801c76b25c4b1ca757109be21af27e2021-11-22T06:30:40ZApplication of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data2673-618710.3389/frsen.2021.791130https://doaj.org/article/ee801c76b25c4b1ca757109be21af27e2021-11-01T00:00:00Zhttps://www.frontiersin.org/articles/10.3389/frsen.2021.791130/fullhttps://doaj.org/toc/2673-6187The Research Scanning Polarimeter (RSP) is an airborne along-track scanner measuring the polarized and total reflectances in 9 spectral channels. The RSP was a prototype for the Aerosol Polarimetery Sensor (APS) launched on-board the NASA Glory satellite. Currently the retrieval algorithms developed for the RSP are being adopted for the measurements of the space-borne polarimeters on the upcoming NASA’s Plankton, Aerosol, Cloud Ocean Ecosystem (PACE) satellite mission. The RSP’s uniquely high angular resolution coupled with the high frequency of measurements allows for characterization of liquid water cloud droplet sizes using the polarized rainbow structure. It also provides geometric constraints on the cumulus cloud’s 2D cross section yielding the cloud’s geometric shape estimates. In this study we further build on the latter technique to develop a new tomographic approach to retrieval of cloud internal structure from remote sensing measurements. While tomography in the strict definition is a technique based on active measurements yielding a tomogram (directional optical thickness as a function of angle and offset of the view ray), we developed a “semi-tomographic” approach in which tomogram of the cloud is estimated from passive observations instead of being measured directly. This tomogram is then converted into 2D spatial distribution of the extinction coefficient using inverse Radon transform (filtered backprojection) which is the standard tomographic procedure used e.g., in medical CT scans. This algorithm is computationally inexpensive compared to techniques relying on highly-multi-dimensional least-square fitting; it does not require iterative 3D RT simulations. The resulting extinction distribution is defined up to an unknown constant factor, so we discuss the ways to calibrate it using additional independent measurements. In the next step we use the profile of the droplet size distribution parameters from the cloud’s side (derived by fitting the polarized rainbows) to convert the 2D extinction distribution into that of the droplet number concentration. We illustrate and validate the proposed technique using 3D-RT-simulated RSP observations of a LES-generated Cu cloud. Quantitative comparisons between the retrieved and the original optical and microphysical parameters are presented.Mikhail D. AlexandrovMikhail D. AlexandrovClaudia EmdeBastiaan Van DiedenhovenBrian CairnsFrontiers Media S.A.articlecloudstomographyradon transformresearch scanning polarimeterreflectanceairborne remote sensingGeophysics. Cosmic physicsQC801-809Meteorology. ClimatologyQC851-999ENFrontiers in Remote Sensing, Vol 2 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	clouds tomography radon transform research scanning polarimeter reflectance airborne remote sensing Geophysics. Cosmic physics QC801-809 Meteorology. Climatology QC851-999
spellingShingle	clouds tomography radon transform research scanning polarimeter reflectance airborne remote sensing Geophysics. Cosmic physics QC801-809 Meteorology. Climatology QC851-999 Mikhail D. Alexandrov Mikhail D. Alexandrov Claudia Emde Bastiaan Van Diedenhoven Brian Cairns Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
description	The Research Scanning Polarimeter (RSP) is an airborne along-track scanner measuring the polarized and total reflectances in 9 spectral channels. The RSP was a prototype for the Aerosol Polarimetery Sensor (APS) launched on-board the NASA Glory satellite. Currently the retrieval algorithms developed for the RSP are being adopted for the measurements of the space-borne polarimeters on the upcoming NASA’s Plankton, Aerosol, Cloud Ocean Ecosystem (PACE) satellite mission. The RSP’s uniquely high angular resolution coupled with the high frequency of measurements allows for characterization of liquid water cloud droplet sizes using the polarized rainbow structure. It also provides geometric constraints on the cumulus cloud’s 2D cross section yielding the cloud’s geometric shape estimates. In this study we further build on the latter technique to develop a new tomographic approach to retrieval of cloud internal structure from remote sensing measurements. While tomography in the strict definition is a technique based on active measurements yielding a tomogram (directional optical thickness as a function of angle and offset of the view ray), we developed a “semi-tomographic” approach in which tomogram of the cloud is estimated from passive observations instead of being measured directly. This tomogram is then converted into 2D spatial distribution of the extinction coefficient using inverse Radon transform (filtered backprojection) which is the standard tomographic procedure used e.g., in medical CT scans. This algorithm is computationally inexpensive compared to techniques relying on highly-multi-dimensional least-square fitting; it does not require iterative 3D RT simulations. The resulting extinction distribution is defined up to an unknown constant factor, so we discuss the ways to calibrate it using additional independent measurements. In the next step we use the profile of the droplet size distribution parameters from the cloud’s side (derived by fitting the polarized rainbows) to convert the 2D extinction distribution into that of the droplet number concentration. We illustrate and validate the proposed technique using 3D-RT-simulated RSP observations of a LES-generated Cu cloud. Quantitative comparisons between the retrieved and the original optical and microphysical parameters are presented.
format	article
author	Mikhail D. Alexandrov Mikhail D. Alexandrov Claudia Emde Bastiaan Van Diedenhoven Brian Cairns
author_facet	Mikhail D. Alexandrov Mikhail D. Alexandrov Claudia Emde Bastiaan Van Diedenhoven Brian Cairns
author_sort	Mikhail D. Alexandrov
title	Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
title_short	Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
title_full	Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
title_fullStr	Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
title_full_unstemmed	Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data
title_sort	application of radon transform to multi-angle measurements made by the research scanning polarimeter: a new approach to cloud tomography. part i: theory and tests on simulated data
publisher	Frontiers Media S.A.
publishDate	2021
url	https://doaj.org/article/ee801c76b25c4b1ca757109be21af27e
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Application of Radon Transform to Multi-Angle Measurements Made by the Research Scanning Polarimeter: A New Approach to Cloud Tomography. Part I: Theory and Tests on Simulated Data

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