Thermal Behavior of CHM15k Ceilometers and Its Statistical Association with Attenuated Backscatter: A Multi-Site ACTRIS Study with Implications for Sustainable Environmental Monitoring

This study investigates the thermal behavior of three Lufft CHM15k ceilometers at ACTRIS observational platforms and evaluates statistical associations between housekeeping temperatures and attenuated backscatter. The instruments are deployed at RADO-Galati and RADO-Bucharest (Romania) and AGORA Granada (Spain). External, internal, optical-module, and detector temperatures from 14 July 2023 to 14 July 2025 were analyzed using Pearson and sliding-window correlations, while time–range correlations assessed associations with the SNR-screened and smoothed attenuated backscatter coefficient. Long-term analysis showed strong external–internal thermal coupling, with clearer seasonal modulation at the Romanian sites than at AGORA–Granada. Five warm- and five cold-season days from 2024 were analyzed per platform. Across the three sites, 51 contiguous regions with strong correlations (|PCC| ≥ 0.8) and at least 50 connected hour–range cells were identified; 47 occurred during warm-season cases and four during cold-season cases. Significant associations were concentrated mainly at lower measurement ranges and extended farther during warm-season cases. These correlations do not demonstrate direct temperature-induced modification of atmospheric backscatter because common diurnal atmospheric variability may contribute. Systematic housekeeping-parameter monitoring can support quality control, preventive maintenance, and resource-efficient operation of long-term atmospheric remote-sensing networks, strengthening sustainable environmental monitoring and resilient research infrastructure relevant to the Sustainable Development Goals (SDGs).