Sorry, I don't understand your search. ×
Back to Search Start Over

On-Orbit Characterization of TanSat Instrument Line Shape Using Observed Solar Spectra

Authors :
Zhaonan Cai
Kang Sun
Dongxu Yang
Yi Liu
Lu Yao
Chao Lin
Xiong Liu
Source :
Remote Sensing, Vol 14, Iss 14, p 3334 (2022)
Publication Year :
2022
Publisher :
MDPI AG, 2022.

Abstract

The Chinese carbon dioxide measurement satellite (TanSat) has collected a large number of measurements in the solar calibration mode. To improve the accuracy of XCO2 retrieval, the Instrument Line Shape (ILS, also known as the slit function) must be accurately determined. In this study, we characterized the on-orbit ILS of TanSat by fitting measured solar irradiance from 2017 to 2018 with a well-calibrated high-spectral-resolution solar reference spectrum. We used various advanced analytical functions and the stretch/sharpen of the tabulated preflight ILS to represent the ILS for each wavelength window, footprint, and band. Using super Gaussian+P7 and the stretch/sharpen functions substantially reduced the fitting residual in O2 A-band and weak CO2 band compared with using the preflight ILS. We found that the difference between the derived ILS width and on-ground preflight ILS was up to −3.5% in the weak CO2 band, depending on footprint and wavelength. The large amplitude of the ILS wings, depending on the wavelength, footprint, and bands, indicated possible uncorrected stray light. Broadening ILS wings will cause additive offset (filling-in) on the deep absorption lines of the spectra, which we confirmed using offline bias correction of the solar-induced fluorescence retrieval. We estimated errors due to the imperfect ILS using simulated TanSat spectra. The results of the simulations showed that XCO2 retrieval is sensitive to errors in the ILS, and 4% uncertainty in the full width of half maximum (FWHM) or 20% uncertainty in the ILS wings can induce an error of up to 1 ppm in the XCO2 retrieval.

Details

Language :
English
ISSN :
20724292
Volume :
14
Issue :
14
Database :
Directory of Open Access Journals
Journal :
Remote Sensing
Publication Type :
Academic Journal
Accession number :
edsdoj.2bf45e6b65c74d1eb1700b0035fe69a9
Document Type :
article
Full Text :
https://doi.org/10.3390/rs14143334