Active–passive collaborative approach for XCO2 retrieval using spaceborne sensors

We propose a novel, to the best of our knowledge, active–passive collaborative retrieval method for measuring XCO2 (APCRM-CO2). This method simultaneously uses observations from spectrometers and integrated path differential absorption laser detection and ranging (IPDA LIDAR), thus making its products have both the coverage advantages of passive detection and the high information content of active detection. The results of simulation experiments show that APCRM-CO2 can reduce the retrieval error by 15% to 70%. The minimum SNR for achieving 1 ppm is 24.7 dB. All these results are obtained without considering the LIDAR measured aerosol profile as input. Therefore, greater performance improvements on XCO2 retrievals are expected in the future for real data processing. The first satellite mission, DQ-2, carrying both a spectrometer and an IPDA LIDAR is planned to be launched by 2025. With the help of APCRM-CO2, its XCO2 products would better assist us with understanding the carbon cycle.