Consideration of the cloud motion for aircraft-based stereographically derived cloud geometry and cloud top heights

Abstract. Cloud geometry and in particular cloud top heights can be derived from 2-D camera measurements by applying a stereographic method to data from an overflight over a scene of clouds (see e.g. Koelling et al., 2019). Although airplane overpasses are relatively fast, cloud motion with the wind is important and can result in errors in the cloud localization. Here, the impact of the wind is investigated using the method from Koelling et al. (2019) for measurements of the airborne hyperspectral imaging system specMACS (spectrometer of the Munich Aerosol Cloud Scanner). Further, a method for the cloud motion correction using model winds from ECMWF is presented. It is shown that the update is important as the original algorithm without the cloud motion correction can over- or underestimate the cloud top heights by several hundred meters dependent on the wind speed and the relative wind direction. This is validated using data from the EUREC⁴A campaign as well as realistic 3-D radiative transfer simulations. From the comparison of the derived cloud top heights to the expected ones from the model input an average accuracy of the cloud top heights of less than (20 ± 140) m (mean deviation and one standard deviation) is estimated for the updated method.