ACDL/DQ-1 calibration algorithms. Part II: daytime 532 nm polarization and high-spectral-resolution channels

The atmospheric environment monitoring satellite (DQ-1) was launched in April 2022, carrying the aerosol and carbon dioxide detection lidar (ACDL) as its primary payload. Following background characterization and nighttime calibration, daytime calibration became necessary because strong solar background radiation and thermal effects complicate daytime observations. This study presents a daytime calibration method for the ACDL 532 nm polarization and high-spectral-resolution channels based on spatiotemporally matched day-night attenuated scattering ratios. Compared with conventional weekly averaging strategies, the proposed method reduces aerosol-related errors caused by prolonged data accumulation. The theoretical systematic uncertainty is about ±7% for the polarization channels and ±6% for the high-spectral-resolution channel. Verification using clear-sky scattering-ratio tests and comparisons with CALIOP observations demonstrates that the mean clear-sky scattering ratio is approximately 1.00, remaining within the theoretical uncertainty range (1±0.11). In addition, the relative difference between ACDL and CALIOP is generally less than 10% below 25 km, confirming the effectiveness and reliability of the proposed daytime calibration method for ACDL daytime observations.