Calibration experiments based on a CO2 absorption cell for the 1.57-µm spaceborne IPDA LIDAR

Abstract

The spaceborne IPDA LIDAR has the potential to measure the global atmosphere CO₂ column concentrations with high accuracy. For this kind of LIDAR, system calibration experiments in the laboratory are of high importance. In this study, a specially-customized CO₂ absorption cell is employed to simulate the CO₂ column absorption of the spaceborne platform. Then calibration experiments are constructed for the receiving system and the entire LIDAR system. The absorption of several different XCO₂ concentrations from 400 to 415 ppm in the atmosphere is equivalent to that of the absorption cell charged with different pressures of pure CO₂. Under the zero pressure of the absorption cell, the calculated equivalent column average concentration (XCO₂) is 12.53 ppm, which acts as system bias. In the calibration experiments, the absolute errors are all less than 1 ppm. And the standard deviations (STDs) are less than 1.1 ppm (148-shot averaging) and 0.8 ppm (296-shot averaging) for receiving system and less than 1.2 ppm and 0.9 ppm for the IPDA LIDAR system. All the results of different average times are close to each other and less than 1 ppm, which proves the high accuracy of the IPDA LIDAR system. In addition, the XCO₂ concentrations Allan deviation of 0.25 ppm and 0.35 ppm at 100 s shows that the receiving system and IPDA LIDAR system function with long-term stability. Using a CO₂ absorption cell as a standard calibration device in the laboratory validates the measurement accuracy and stability of the spaceborne IPDA LIDAR prototype. Furthermore, the proposed absorption cell may serve as a standard calibration device for related atmosphere trace gases sounding research.