Inflight Performance of the TanSat Atmospheric Carbon Dioxide Grating Spectrometer

• Published in: IEEE transactions on geoscience and remote sensing Vol. 58; no. 7; pp. 4691 - 4703
• Main Authors: Yang, Zhongdong, Bi, Yan-Meng, Wang, Qian, Liu, Cheng-Bao, Gu, Song-Yan, Zheng, Yuquan, Lin, Chao, Yin, Zengshan, Tian, Longfei
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.07.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Absorption spectra; Accuracy; Atmosphere; Atmospheric measurements; Calibration; Carbon dioxide; Extraterrestrial measurements; Gratings; Greenhouse effect; Instruments; Noise; Noise levels; Oxygen; Prelaunch tests; Resolution; Satellites; Signal to noise ratio; sounding; Spectral bands; spectrometer; Sunlight; Wavelength
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/TGRS.2020.2966113

TanSat was successfully launched on December 22, 2016, and has been acquiring global measurements of CO 2 and O 2 spectral bands in reflected sunlight since early February 2017. The atmospheric carbon dioxide grating spectrometer (ACGS) is a spaceborne three-band grating hyperspectral spectrometer suite onboard TanSat. The ACGS is designed to measure high-spectral-resolution, coboresighted spectra of reflected sunlight within the molecular oxygen (O 2 ) A-band range from 0.758 to 0.778 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> and the weak and strong absorption bands of carbon dioxide (WCO 2 and SCO 2 ) ranging from 1.594 to 1.624 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> and from 2.042 to 2.082 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>, respectively. The spectral resolving power (<inline-formula> <tex-math notation="LaTeX">\lambda /\Delta \lambda </tex-math></inline-formula>) of the ACGS is ~19 000, ~12 800 and ~12 250 in the O 2 A-band, WCO 2 band and SCO 2 band, respectively. The inflight radiometric calibration accuracy is better than 5%, which satisfies the required specification. The wavelength calibration accuracy of the O 2 A-band is ~0.19 pm, that of the WCO 2 band is ~0.27 pm, and that of the SCO 2 band is ~4.75 pm, all of which meet the 0.05 full-width at half-maximum (FWHM) requirement. The spectroscopic performance of the ACGS exceeds the mission requirements by a margin. The ACGS has noise levels that are comparable to or smaller than those observed during prelaunch testing, and the noise has remained stable in the three bands during inflight operations. The signal-to-noise ratio (SNR) levels of the three bands meet the specified requirements. As expected, the ACGS radiometric performance in the O 2 A, WCO 2 , and SCO 2 bands was fairly good during its first 17 months inflight.