Design of Inversion Procedure for the Airborne CO₂-IPDA LIDAR: A Preliminary Study

China will launch the Atmospheric Environment Monitoring Satellite, which is equipped with a CO2-IPDA LIDAR. It is of great significance to explore the feasibility and effectiveness of this novel technique and to identify potential differences among its CO2 concentration products and the passive remote sensing technique. In this work, we developed an initial data-processing procedure for an airborne CO2-IPDA LIDAR, which is the minified prototype of the forthcoming space-borne LIDAR. We tested the effectiveness of this procedure and evaluated the performance of the minified prototype in a flight test over ocean, urban and mountainous terrain. The column-weighted xCO2 (XXCO2) retrievals obtained by the airborne IPDA-LIDAR were considerably more sensitive to the gradients of the dry-air mixing ratio of CO2 (xCO2), compared with both the XCO2 products of OCO-2 and in-situ measurements of point xCO2. The mean XXCO2 over the ocean, urban and mountainous area are 412.02, 438.32 and 433.08 ppm with STDs of 1.35, 0.75 and 0.91 ppm, respectively. We also used altitude-dependent xCO2 obtained by a decline-climb flight to calculate a reference for XXCO2 over the ocean. The difference between XXCO2 obtained via two means was less than 0.5 ppm. Moreover, our performance evaluation model predicted that a relative random error of less than 0.3% would be very likely for the forthcoming satellite mission over land. However, measuring CO2 concentrations precisely over oceans is identified as a very challenging work. Thus, developing dedicated algorithms to address CO2 measurement over oceans by using the IPDA-LIDAR is necessary.