Radar Observations and Radar Model Computations of Biological Scatterers

Polarimetric Doppler radar measurements of biological scatterers show distinct characteristics. Biological scatterers can be identified as a fine line of enhanced polarimetric radar signatures. Typically echoes from biological scatterers are present between ground and 1 km AGL. Reflectivity values typically vary between 5 and 20 dBZ and they are directly proportional to size and number concentration. Differential polarimetric measurements, namely, Zdr and differential propagation phase (ΦDP ) are sensitive to shape and size. Polarimetric measurements of biological scatterers can be separated into signatures of insect and birds based on radial velocity, differential backscatter phase observation (δHV) that is inferred from ΦDP.

In this paper radar measurements and model computations of biological scatters are shown. As radar measurements are sensitive to orientation and size of biological scatterers, scattering computations of biological scatters are compared with radar measurements for inferring size, type and orientation of biological scatters. Radar scattering computations of birds and insects of various sizes are shown as a function of aspect angle. At small sizes cross-sections smoothly varies as a function of aspect angle. Radar cross-section is proportional to physical cross-section of a bird when the size of a bird is small compared to wavelength. As size of biological scatterers become comparable to radar wavelength radar cross section varies by 10 dB as the aspect angle changes.