Frequency Selection and Detection Efficiency of Forward-Looking Miniaturized Millimeter-wave Radiometer for Icing Detection from Airborne Platforms

Aircraft icing due to super-cooled liquid water poses a serious threat to aircraft flying through clouds. The water droplets freeze upon contact with the aircraft frame, causing a change in wing geometry resulting in loss of lift, increased drag, and loss of aircraft attitude control, often leading to severe damage to the air frame. Large aircraft carry deicing equipment to reduce the probability of icing. However, this is not a practical solution for smaller aircraft like helicopters and UAVs, due to size constraints. The normal procedure is to declare no-fly zones over large areas and ground smaller aircraft when icing clouds are forecast. However, forecasts of the presence of super-cooled clouds are not always accurate, leading to the loss of flight time and resources, especially considering the increasing usage of UAVs and smaller aircraft in recent years. A better method to address this problem is needed, in which an aircraft modifies its flight path only when there is a significant probability of super-cooled water in the clouds. Since the temperature of the cloud droplets is needed to find the probability of super-cooled water, microwave radiometry is chosen as a suitable method of detection. To provide sensors with appropriate size for smaller aircraft, millimeter-wave frequencies are chosen over lower microwave frequencies. Therefore, forward-looking millimeter-wave radiometers on airborne platforms are a good candidate to detect the probability of super-cooled water droplets in clouds and also gauge their proximity to the airborne platform. In this way, the aircraft needs to avoid only the clouds that are likely to pose a threat. This can also provide access to large swaths of airspace that are typically inaccessible to small aircraft. In the design of such a millimeter-wave radiometer for detection of the probability of super-cooled water, both frequency selection and detection efficiency need to be evaluated. ARTS (Atmospheric Radiative Transfer Simulator) is a radiative transfer model used to simulate atmospheric scenarios to select millimeter-wave frequencies and their efficiency for super-cooled liquid water detection. ARTS is used to identify suitable sets of millimeter-wave radiometer frequencies and their potential for detection as well as sensitivity to the proximity of the cloud to the sensor.