Observations of Insects and Birds with a Polarimetric Prototype of the WSR-88D Radar

Clear air echoes over extended periods of time have been observed with the KOUN polarimetric radar in 2004 with the goal to separate passive tracers (insects or refractive index irregularities) from vigorous flyers such as birds. These observations occurred mainly in spring and fall and reveal several important features of biological scatterers. On 8 September 2004 in 24 hours of continuous operations evident are abrupt changes at sunrise and sunset of differential reflectivity and differential phase. Both types of scatterers are present during day and night. Repetitive and predictable behavior of diurnal birds is motivated by the need for food hence they depart and return to roosting which is clearly visible in the fields of polarimetric variables. Further, hovering over urban area also produces characteristic patterns in time and location. Nocturnal birds migrate in spring and fall hence causing strong echoes with definite polarimetric signatures over very wide areas. Asymmetric azimuthal dependence of observed polarimetric variables and the orientations of migrating birds and insects are discussed and investigated. Observations of layered insect and bird echoes are also reported. Besides polarimetric variables the Doppler velocities provide some clues to the behavior of the two different species and confirm polarimetric measurements.