Abstract
The radar scattering characteristics of aerial animals are typically obtained from controlled laboratory measurements of a freshly harvested specimen. These measurements are tedious to perform, difficult to replicate, and typically yield only a small subset of the full azimuthal, elevational, and polarimetric radio scattering data. As an alternative, biological applications of radar often assume that the radar cross sections of flying animals are isotropic, since sophisticated computer models are required to estimate the 3D scattering properties of objects having complex shapes. Using the method of moments implemented in the WIPL-D software package, we show for the first time that such electromagnetic modeling techniques (typically applied to man-made objects) can accurately predict organismal radio scattering characteristics from an anatomical model: here the Brazilian free-tailed bat (Tadarida brasiliensis). The simulated scattering properties of the bat agree with controlled measurements and radar observations made during a field study of bats in flight. This numerical technique can produce the full angular set of quantitative polarimetric scattering characteristics, while eliminating many practical difficulties associated with physical measurements. Such a modeling framework can be applied for bird, bat, and insect species, and will help drive a shift in radar biology from a largely qualitative and phenomenological science toward quantitative estimation of animal densities and taxonomic identification.
Highlights
The most common quantitative application of weather radar in biology has been for estimating animal densities, passage rates, or population sizes[2,13]
We examined the dual-polarization radio-wave scattering properties of the Brazilian free-tailed bat (Tadarida brasiliensis) using laboratory measurements, field observations, and computer modeling
The electromagnetic (EM) model reliably represents the radar cross-section (RCS) of the studied bat species
Summary
The most common quantitative application of weather radar in biology has been for estimating animal densities, passage rates, or population sizes[2,13]. In these applications, the scattering contribution of individual animals is characterized by their radar cross-section (RCS), which is a measure of the power density of the scattered electric field relative to that which was incident on the object[14]. The paucity of available biological RCS data at diverse view angles and polarizations, especially for vertebrates, can primarily be attributed to the complexity of obtaining such measurements through laboratory and field observations. Comparisons of the model scattering calculations with controlled measurements and field observations serve to validate the model performance and demonstrate its utility in biological radar applications
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