Radar has been successfully used for over twenty years to study the flight behaviour of a variety of migrant insects. However, the complexity of the equipment and the time-consuming nature of data analysis procedures have precluded use of the technique for routine, long-term monitoring. We report here the development of a technique specifically intended to make such routine monitoring a practical proposition. The 3 cm radar transmits a vertical-looking beam which nutates about a vertical axis, and in which the plane of linear polarization is rotated. Overflying insects modulate the radar signal in a way which is related to their speed and direction of movement, their orientation, size, and shape. We have shown that all these parameters can be extracted from the complex Fourier transform of the returned radar signal, by using appropriate 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.
Philosophical Transactions of the Royal Society of London B (1993) 340 (1294) 393-404 [doi: 10.1098/rstb.1993.0081]