Geometric correction for TanSat atmospheric carbon dioxide grating spectrometer

Abstract

Carbon Observing Satellite (TanSat) is the first of Chinese experimental satellite for monitoring the CO2 column densities in the atmospheric, while identifying sources and sinks on regions scales. Three grating spectrometers are equipped on TanSat to measure the reflected sunlight in the 0.76μm O2A-band, 1.61μm weak CO2 band and 2.06μm strong CO2 band respectively. Three bands have high spectral resolution and signal to noise ratio (SNR), while their spectral and radiometric calibration have been reported in many articles. This paper describes the geometric calibration of the essential payload (ACGS) on the TanSat. In the assembly process, the flatness only in the spatial dimension is strictly controlled owing to the physical obstruction. The geometric deflection error in one band should be tested and corrected by adjusting the starting rows of different spectral samplings. Meanwhile, the alignment error among the three bands also need processing in the same way to ensure that the slits of the three bands were matched the corresponding geographic target. Finally, the geometric correction results of the thermal-vacuum testing suggested that the alignment accuracy is well enough to match the requirements.