Comparative analysis of optical in-situ probes and the MSG satellite for improved detection of aircraft icing conditions

Kurzfassung

In-flight icing poses a significant threat to aircraft safety, potentially leading to the distortion of airflow over wings, loss of lift force, reduced speed, and even stall. While current aircraft are equipped with protection systems against icing, supercooled large droplets (SLDs) still present a safety hazard as they can impinge behind the protected surfaces of an aircraft. To detect and understand the characteristics of SLD conditions, airborne in-situ measurements provide a comprehensive examination of cloud microphysical properties using sensors mounted on an aircraft. One well-established instrument for measuring cloud particles is the Cloud Imaging Probe (CIP), which has been widely used for cloud measurements. However, it is associated with measurement uncertainties. A newer 2D imaging probe, the High-Speed Imager (HSI), is designed to address some of the limitations of the CIP. The CIP and HSI probes were integrated into SAFIRE's research aircraft ATR-42 during the SENS4ICE flight campaign conducted in Southern France in April 2023. These in-situ measurements served as reference data for the validation of new ice detection sensors. The primary objective of this study is to develop a methodology aimed at evaluating CIP measurements, particularly in finding out SLDs and large droplet icing conditions following the criteria outlined in Appendix O of aircraft certification standards. The processed data and images from a selected icing encounter are then compared with the HSI data to discriminate their measurement characteristics. The findings can provide support for future flight campaigns to choose the suitable instrument. The presented data evaluation procedure is then demonstrated on an observational flight of the SENS4ICE campaign. An incoming warm front system with a high likelihood of containing SLD is sampled throughout the flight. Cloud measurements were conducted at temperatures ranging from 0 to -15 degrees Celsius and altitudes below 5 km. The proposed methodology effectively detected large droplet icing conditions, which extended for nearly an hour. Additionally, the in-situ cloud data collected was used to characterize atmospheric conditions conducive to SLD formation. The results were subsequently cross-validated with Meteosat Second Generation (MSG) satellite products to enable a comprehensive analysis. The tool utilized predominantly categorized the cloud-top of the sampled clouds as mixed-phase. However, the confidence level in these classifications is relatively low due to the obstruction caused by higher-level clouds, limiting the satellite’s observation of the cloud system.