CONIOPOL: A novel operational approach for real-time aerosol/cloud identification using CL61 depolarization measurements

Accurate identification of aerosol type and cloud phase is essential for understanding atmospheric processes, radiative forcing, and aerosol–cloud interactions, especially during long-range transport events such as Saharan dust intrusions and transatlantic wildfire smoke. Recent advances in automatic lidar–ceilometers (ALCs) equipped with depolarization capability, such as the Vaisala CL61, enable continuous and unattended monitoring of aerosol type and cloud phase at high temporal and vertical resolution. However, single-wavelength configurations limit the exploitation of multi-parameter aerosol classification methods developed for advanced multi-wavelength lidars.

 

At the Royal Meteorological Institute of Belgium (RMI), we developed CONIOPOL (CONIOlogy + POLarization), an algorithm that exploits backscatter and depolarization profiles from the Vaisala CL61. By combining attenuated backscatter, linear depolarization ratio (LDR), and cloud-base height retrievals, CONIOPOL discriminates between clouds, precipitation, and aerosols, and classifies cloud phase, precipitation type, and major aerosol subtypes in near real time. Despite the spectral limitation, the algorithm demonstrates strong temporal and vertical coherence with CAMS forecasts, effectively capturing key aerosol transport events and seasonal variability over Belgium.

 

This presentation highlights CONIOPOL’s performance through high-impact case studies, long-term statistical analyses, and direct comparisons with CAMS forecasts and surface air quality observations. We focus on the detection of distinct aerosol types—including dust and smoke—and their vertical and seasonal distributions. Beyond operational applications, CONIOPOL enables the construction of consistent aerosol and cloud climatologies from continuous ALC observations, bridging gaps between satellite, in situ, and advanced lidar measurements. These results underscore the potential of depolarization-capable ceilometers to support long-term aerosol monitoring, improve understanding of aerosol–cloud interactions, and enhance air-quality climatologies.