Measuring refractivity profiles using shipborne unmanned aerial vehicle

Accurate characterization of the refractive conditions is important for electromagnetic (EM) propagation prediction in the marine atmospheric boundary layer (MABL). Especially anomalous refractive conditions, such as ducts, which for example may cause extended range for ship-borne radar and radio communication systems, are important to map. The use of unmanned aerial vehicles (UAVs) provides new opportunities to conduct ship-borne measurements of high-resolution vertical profiles of modified refractivity (M) in the MABL, which is challenging to achieve with traditional methods. Equipped with purpose-built meteorological sensors, UAVs can effectively provide multiple, high-resolution, vertical profiles from close to the sea surface (1–2 m) and upwards, i.e. they can be used to locate both evaporation, surface and elevated ducts. In this work we present the observations from an iMet-XQ2 sensor mounted on a SkyRanger R70 UAV during a sea trial off the southeast coast of Norway in June 2022. Several high-resolution vertical profiles of pressure, temperature and relative humidity were collected during three flights, with resulting M-profiles that varied within and in between flights, thus revealing the complexity of the MABL. An elevated duct was observed in several of the measurements, which to some extent correlated with the output from the AROME-MetCoOp numerical weather prediction model. Evaporation ducts were present in 92 % of the M-profiles, with highly variable evaporation duct heights.