A METHOD FOR ROUTINE MONITORING OF THE AERIAL MIGRATION OF INSECTS BYUSING A VERTICAL-LOOKING RADAR

Radar has been successfully used for over twenty years to study the fl ight behaviour of a variety of migrant insects. However, the complexit y of the equipment and the time-consuming nature of data analysis proc edures have precluded use of the technique for routine, long-term moni toring. We report here the development of a technique specifically int ended to make such routine monitoring a practical proposition. The 3 c m radar transmits a vertical-looking beam which nutates about a vertic al axis, and in which the plane of linear polarization is rotated. Ove rflying insects modulate the radar signal in a way which is related to their speed and direction of movement, their orientation, size, and s hape. We have shown that all these parameters can be extracted from th e complex Fourier transform of the returned radar signal, by using app ropriate algorithms on a modern desk-top computer. The success of this development means that economic, automatic, and long-term monitoring of the density, direction of movement, orientation and composition of insect aerial faunas should now be possible.