Linear-Fitting calibration algorithm for Aerosol-Cloud detection channels at 532 nm of the DQ-1/ACDL

The Aerosol and Carbon Detection Lidar (ACDL) aboard the DQ-1 satellite is a new-generation spaceborne high-spectral-resolution lidar (HSRL) with 532 and 1064 nm channels for aerosol and cloud observations. The calibration at 532 nm is the foundation for producing ACDL products. However, ACDL lacks direct background-noise measurements, which limits the applicability of conventional calibration approaches. To address this issue, we propose a linear-fitting calibration method that uses multiple clear-air altitude bins to solve simultaneously for the calibration coefficient and the background offset. Nighttime calibration is performed in clear-air regions at 34–38 km, while daytime calibration uses a clear-air calibration-transfer region located 2–6 km above the 400 K isentropic surface. The calibration results show that the total and molecular-channel attenuated scattering ratios (ASRs) were approximately 1 at 30–34 km, for both nighttime and daytime observations, indicating the effectiveness of the method. A one-month cross-validation was conducted by comparing the total attenuated backscatter (TAB) of ACDL, derived from different calibration methods, with NASA CALIPSO/CALIOP products. The ACDL TAB obtained by the linear-fitting method is consistent with CALIOP during both nighttime and daytime, with mean deviations of about −0.3 % and −1.6 % above 10 km, respectively, whereas the conventional ratio method yields deviations more than an order of magnitude larger when background noise is estimated above 35 km. This work resolves ACDL’s calibration challenges at 532 nm and establishes a foundation for reliable aerosol and cloud products that support future atmospheric and climate research.