Derivation of aerial insect concentration with a 94 GHz FMCW cloud radar

Abstract

Aerial insects are vital for nature and society. Though methods to observe flying insects have consistently improved in the last decades, insects remain difficult to monitor systematically and consistently over large spatial and temporal scales. Remote sensing with radars has proved to be one of the more effective tools for observation. However, as radars are most sensitive to targets that are of similar size to the radar wavelength, the detectable sub-group of aerial insects of a certain size range depends on the employed radar. Here, we present a novel method based on spectral data of zenith-pointing Doppler cloud radars to estimate insect concentration in a vertical profile. Multiple meteorological state-of-the-art algorithms are combined to extract insect signals from the radar data and quantify their abundance from 150 m to 3000 m above the ground. For evaluation, this method is applied to triple frequency data from X-band ({lambda} = 3.2 cm), Ka-band ({lambda} = 0.85 cm) and W-band ({lambda} = 0.32 cm) Doppler cloud radars from a three months summertime observation period in Germany. Observations of a case study of two elevated aerial insect layers are presented. Furthermore, differences in diel cycles of aerial insect concentration (aic) obtained from the three radar instruments are compared. With its superior sensitivity to very small insects like aphids, W-band shows the highest aerial insect concentrations during day-time in the lower altitudes. Generally, the higher wavelength radars show higher aerial insect concentrations in higher altitudes (Ka-band) and during the night (X-band).