|Paper title||IASI radiometric error budget assessment and exploring inter-comparisons between IASI sounders using acquisitions of the Moon|
|Form of presentation||Poster|
IASI radiometric error budget assessment and exploring inter-comparisons
between IASI sounders using acquisitions of the Moon
IASI (Infrared Atmospheric Sounding Interferometer) instruments on-board METOP polar orbiting meteorological satellites are currently used for climate studies [1-3]. IASI-A launched in 2006, displayed 15 years of stable performances and is no longer active. There are still two operational IASI instruments: one on-board METOP-B (launched in 2012) and one on-board METOP-C (launched in 2018). Efforts are continuously being made by CNES to improve IASI data quality during their whole lifetime. For example, the methodology for the spectral calibration was improved for IASI-A and a recent reprocessing was performed by EUMETSAT in order to obtain continuous homogeneous data series for climate studies. Moreover, the on-board processing non-linearity corrections for both IASI-A and IASI-B instruments were improved in 2017, reducing the NedT error in the spectral band B1.
IASI is the reference used by the GSICS (Global Space based Inter-Calibration System) community for inter-comparisons between infrared sounders to improve climate monitoring and weather forecasting. The objective here is to present the errors sources which impact the IASI radiometric error budget considering the uncertainties related to the knowledge of the internal black body (e.g. temperature and emissivity), the non-linearity correction and the scan mirror reflectivity law. This work is performed in the framework of the collaboration with the GSICS community to ensure a stable traceability of infrared sounders radiometric and spectral performances.
Moreover, Moon data are regularly acquired since 2019 by IASI-B and IASI-C to study the possibility to perform absolute and relative calibrations by using these lunar observations. The Moon is often used in the visible domain as a calibration source for satellite instruments, but, until now, it is not the case in the thermal infrared domain. In the framework of this study, a dedicated radiometric model was built to simulate and compare IASI lunar measurements. Inter-comparisons between IASI-B and IASI-C Moon acquisitions showed really promising results with an accuracy of ≤ 0,15K. These results are comparable to the performance of IASI instruments inter-comparisons based on selected homogeneous Earth View spectra.
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 Simon Whitburn and co, Trends in spectrally resolved outgoing longwave radiation from 10 years of satellite measurements, npj Climate and Atmospheric Science 4, article number 48 (2021)
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