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Emissivity retrievals with FORUM's end-to-end simulator: challenges and recommendations

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Title: Emissivity retrievals with FORUM's end-to-end simulator: challenges and recommendations
Authors: Ben-Yami, M
Oetjen, H
Brindley, H
Cossich, W
Lajas, D
Maestri, T
Magurno, D
Raspollini, P
Sgheri, L
Warwick, L
Item Type: Journal Article
Abstract: Spectral emissivity is a key property of the Earth's surface, of which only very few measurements exist so far in the far-infrared (FIR) spectral region, even though recent work has shown that the FIR is important for accurate modelling of the global climate. The European Space Agency's 9th Earth Explorer, FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will provide the first global spectrally resolved measurements of the Earth's top-of-the-atmosphere (TOA) spectrum in the FIR. In clear-sky conditions with low water vapour content, these measurements will provide a unique opportunity to retrieve spectrally resolved FIR surface emissivity. In preparation for the FORUM mission with an expected launch in 2027, this study takes the first steps towards the development of an operational emissivity retrieval for FORUM by investigating the sensitivity of the emissivity product of a full spectrum optimal estimation retrieval method to different physical and operational parameters. The tool used for the sensitivity tests is the FORUM mission's end-to-end simulator. These tests show that the spectral emissivity of most surface types can be retrieved for dry scenes in the 350–600 cm−1 region, with an absolute uncertainty ranging from 0.005 to 0.01. In addition, the quality of the retrieval is quantified with respect to the precipitable water vapour content of the scene, and the uncertainty caused by the correlation of emissivity with surface temperature is investigated. Based on these investigations, a road map is recommended for the development of the operational emissivity product.
Issue Date: 23-Mar-2022
Date of Acceptance: 18-Feb-2022
URI: http://hdl.handle.net/10044/1/96225
DOI: 10.5194/amt-15-1755-2022
ISSN: 1867-1381
Publisher: Copernicus Publications
Start Page: 1755
End Page: 1777
Journal / Book Title: Atmospheric Measurement Techniques
Volume: 15
Issue: 6
Copyright Statement: © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0/)
Sponsor/Funder: Natural Environment Research Council (NERC)
European Space Agency / Estec
Funder's Grant Number: JJR/NCEO/ContFP1
Keywords: Meteorology & Atmospheric Sciences
0401 Atmospheric Sciences
Publication Status: Published
Open Access location: https://doi.org/10.5194/amt-15-1755-2022
Appears in Collections:Space and Atmospheric Physics

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