Improvement of DQ-1/ACDL in Global Thin Cirrus Cloud Detection

Lidar is an essential and unique tool in the current integrated spaceborne remote sensing observation system. From CALIPSO-CloudSat in the A-Train constellation to China’s Daqi-1 (DQ-1) and the latest EarthCARE mission, lidar’s ability to detect thin cirrus and low clouds with fine vertical resolution has significant implications. The effective combination of lidar and CPR provides a complete cloud vertical structure for related studies and an accurate validation for passive remote sensors.

Launched successfully on April 16, 2022, the DQ-1 satellite carries the Aerosol Carbon Detection Lidar (ACDL), a three-wavelength  (532, 1064, and 1572 nm) lidar for comprehensive measurements of atmosphere composition. is technically a combination of two lidars with different mechanisms: a high-spectral-resolution lidar (HSRL) measuring clouds and aerosols and an integrated-path differential absorption (IPDA) lidar measuring carbon dioxide. The mechanism of HSRL allows the separation of aerosol contribution from the molecular backscatter, therefore removing the lidar ratio assumption in the traditional Mie-scattering lidar like CALIOP. Initial validation results indicate an accuracy better than 20% for a strong signal backscatter profile with 24 m vertical resolution. The cloud-top and base height, phase, and classification products have been processed accordingly.

Positioned time-wise between CALIPSO and EarthCARE missions, DQ-1 fills a critical gap in the observation and cross-validation. This report contains results from a one-year-long comparison between DQ-1/ACDL and CALIPSO/CALIOP from June 2022 to June 2023, till the end of CALIPSO operation. The analysis includes case studies from different latitudes and scenarios, and overall gridded global thin cirrus cloud distributions. The results show good consistency between the two systems, with DQ-1/ACDL demonstrating better coherence and performance. Depending on data availability, the report might also include preliminary comparisons with EarthCARE/ATLID data. The report will highlight key improvements of the DQ-1/ACDL system in thin cirrus cloud detection, for better monitoring and valuable insights of cloud properties, atmospheric dynamics, and climate modeling.