Processing of Doppler Spectra Collected by an Airborne Cloud Radar for the Calculation of Skewness, Kurtosis, and Other Spectral Parameters

Abstract

Observations from the HIAPER Cloud Radar (HCR) are used to develop a methodology to calculate Doppler spectra from an airborne platform. The method removes spectral noise and corrects the spectra for broadening caused by aircraft motion. The spectra are filtered using an objectively optimized filtering technique. The de-noised and corrected spectra are used to calculate qualitatively improved spectrum width, skewness, and kurtosis. These higher-order moments are supplemented by other spectral parameters such as edge-to-edge width, left and right spectral slope, and left- and right-edge velocity. Regions with dual-peak spectra are also identified. The higher-order moments and other spectral parameters highlight cloud features that are not apparent in the lower-order moments reflectivity and Doppler velocity. They provide additional information which can be used to derive cloud microphysical and kinematic properties as they reduce the ambiguity of radar observations. The processing technique is applied to observations collected in different climatic regions ranging from the tropics to the Southern Ocean. It proves robust and produces high-quality observations for a wide range of cloud types.