Development of spaceborne high-spectral-resolution lidar retrieval algorithm for ACDL/DQ-1 aerosols and clouds observation: improvements and analysis

The Aerosol and Carbon Detection Lidar (ACDL), which onboard Chinese atmospheric environment monitoring satellite DQ-1, is the first spaceborne lidar that employs an iodine molecular filter for high-spectral-resolution detection. In its atmospheric observation mission, it is equipped with a 532 nm parallel polarization channel, a 532 nm cross polarization channel, a 532 nm molecular channel, and a 1064 nm detection channel, enabling the direct retrieval of aerosol and cloud optical properties. ACDL has been operating stably for over three and a half years, continuously accumulating vertical profile data on aerosols and clouds. The scientific team is committed to continuously optimizing the algorithms by leveraging its unique dual-pulse laser emission scheme and the characteristics of observational data from each channel. The latest developed Baseline05 retrieval algorithm achieves higher resolution, increased valid data volume, and improved day—night consistency. Following the data flow design, the Baseline05 algorithm performs direct retrieval from raw signals (Level 1 A) to atmospheric optical parameters (Level 2 C). The data products have a vertical resolution of 50 m, and horizontal resolutions of 3.3 km at night and 6.6 km during daytime. Baseline05 improves the data pre-processing flow, with a focus on optimizing the background signal extraction and calibration scheme. In the retrieval module, Baseline05 fully exploits the high-spectral-resolution detection capability of the ACDL molecular channel, utilizing simulated ideal atmospheric signals to optimize the segmented denoising for each channel. It also innovatively develops a layer identification and iterative retrieval algorithm, enabling the identification and retrieval of stratospheric, high-latitude, and multiple thin aerosol and cloud layers. Using data product examples from nighttime and daytime observation orbits, a comparative analysis illustrates the improvements of Baseline05 in layer identification and in the retrieval of key optical parameters such as the depolarization ratio, lidar ratio, and attenuated colour ratio. The new retrieval algorithm will effectively enhance ACDL’s aerosol and cloud observation capabilities, providing a technical foundation for subsequent Level 3 product development and atmospheric pollution monitoring.