Using a dual-polarimetric weather radar simulator to investigate microwave backscatter from birds

The capacity of radars to detect biological targets in the aerosphere has been known for 50 years and NEXRAD has been used in this manner for 20 years. Biological targets typically detected include birds, bats, and insects, which in some cases reflect local conditions and/or animal migration. Despite this history of biological use, there remain persistent and significant limitations in using the existing NEXRAD system for biological monitoring. In part, these problems stem from 1) the lack of a robust biological nexus within the radar community, 2) the current limited ability of NEXRAD to reliably discriminate among targets of different taxonomic origins, 3) the manner in which the data are filtered before being released to the public, and 4) a paucity of available funds to adequately explore this topic. In addition to limiting the biological value of radar data, the failure to cleanly separate biological and meteorological targets in existing radar data compromises the quality of weather monitoring and forecasting.

In order to confront some of these limitations, a weather radar simulator developed by researchers at the University of Oklahoma (OU) has recently been modified to include the effects of backscatter from birds. The simulator provides a platform that allows quasi-realistic interactions of dual-polarimetric microwaves with individual “virtual birds” placed within the sampling domain and which produce raw (in-phase and quadrature) data streams corresponding to the backscattered radar signals. In the current version of the simulator, it is possible to model birds of various sizes, aspect ratios, spatial distributions, and flight speeds. There is also a means of accounting for the time varying wing beat frequencies of the virtual birds. The ability to study echoes from the virtual birds under a controlled environment will lead to a better understanding of how radio waves interact with actual birds. Results from the weather radar simulator will ultimately be compared to real dual-polarimetric weather radars operating at C- and S-band. Such a study is particularly timely considering the future polarimetric upgrade of the NEXRAD network. For this presentation, we will begin by discussing the simulator and the modifications that were necessary to account for scatter from birds. After showing results from the simulator, various applications (meteorological and biological) and future research directions will be considered.