Research on calculation method of on-orbit instrumental line shape function for the Greenhouse Gases Monitoring Instrument on the GaoFen-5B satellite

Abstract

The Greenhouse Gases Monitoring Instrument is based on the spectroscopic principle of spatial heterodyne spectroscopy technology and has the characteristics of no moving parts, hyperspectral resolution, and large luminous flux. The instrumental line shape function is one of the important parameters characterizing the characteristics of the instrument and plays a vital role in the system error analysis of instrument measurement. To accurately obtain the instrumental line shape function of the spatial heterodyne spectrometer during on-orbit period and improve the accuracy of gas concentration retrieval, this paper develops a method to model and characterize the characteristics of the instrumental line shape function, including modulation loss and phase error. Utilizes the stability of solar observation spectrum wavelength and is not influenced by additional conditions to update the instrument line function. The Kurucz solar spectrum model used as the theoretical reference spectrum, selects the characteristic spectral lines corresponding to the measured solar calibration spectrum and the reference spectrum in the 1.568~1.583 μm band, and adjusts the instrumental line shape function model parameters, iterates the characteristic spectral lines residual, and calculates the instrumental line shape function variations. The updated instrumental line shape function has increased the average relative deviation between the theoretical simulated and measured solar spectrum from 1.83% to 0.756%, and the average relative deviation between the nadir observation spectrum and the simulated spectrum has increased from 7.049% to 2.106%. The findings demonstrate that updating the instrumental line shape function mitigates the impact of variations in the spectrometer's instrumental line shape due to alterations in the orbital environment. This offers a dependable reference for both the enhancement and oversight of the spectrometer's instrumental line shape function, along with the investigation of shifts in instrument parameters.