Laboratory spectral calibration of TanSat and the influence of multiplex merging of pixels

ABSTRACT This article first reviews the main characteristics of the High-Resolution Hyperspectral Sensor for carbon observation Grating Spectrometer (HRHS-GS) and discusses the impact of spectral resolution on gas absorption lines. The major content of this article is the laboratory calibration of HRHS-GS, the signal-to-noise ratio (SNR), instrument line shape (ILS), and the spectral resolution of each channel were achieved. The SNR results met the mission requirements for the 0.76 µm band, but missed the requirement for the two Carbon dioxide (CO2) bands. To address this problem, the model ‘Multiplex Merging of Spectral Pixels’ was established to improve the SNR by increasing the incident energy of a single spectral channel. This process would lead to spectral broadening; the spectral resolution before and after that process was obtained. The transmittance spectra before and after multiplex merging were compared by the line-by-line radiative transfer model (LBLRTM) to analyse the impact of spectral broadening on gas absorption lines. Next, the results were verified by experiment with a gas absorption cell. The results showed that ‘Multiplex Merging of Spectral Pixels’ could effectively improve the SNR. For the 0.76 µm band, the transmittance spectra before and after multiplex merging were almost the same; for the 1.61 µm band, the peak value of the transmittance spectra decays by about 5%; and for the 2.06 µm band, the attenuation of the transmittance spectra is smaller than 3%. Meanwhile, the spectral resolution after spectral broadening still satisfied the study’s requirement.