Williams, Johnson, Giangrande, Hardin, Öktem, and Romps, Identifying insects, clouds, and precipitation using vertically pointing polarimetric radar Doppler velocity spectra, AMT, 2021





Weather radars are designed to tell us about the spatial distribution of condensed water (e.g., cloud droplets, rain, and snow). A radar sends out a pulse of electromagnetic radiation and then "listens" for the echo of that radiation scattering off the condensed water. By measuring the time that elapses between emitting the pulse and "hearing" its echo, the radar can calculate how far away that condensed water is.

Unfortunately, particles of liquid water and ice are not the only things that reflect those radar pulses. Insects can, too. That causes the radar data to be contaminated with return pulses from insects, and a cloud of insects is often hard to distinguish from a cloud of liquid water. To solve that problem, first-author Christopher Williams identifies an algorithm that can use additional information in the returned radar pulses to tell insects apart from cloud droplets. To confirm that the algorithm works, we have compared the algorithm's reported clouds with the range of cloud heights reported by our stereo cameras (in particular, our Clouds Optically Gridded by Stereo product, or COGS).

(top) The red and blue plus signs show the minimum and maximum heights of clouds as detected by COGS. The maroon color indicates where the radar is reporting cloud. Note that there are many detections outside of the COGS range; these are insects. (bottom) Same, but after passing the radar data through Dr. Williams' new algorithm. The radar's reports of cloud are now much more consistent with COGS.