Measurement of point target speeds with incoherent non-tracking radar: Insect speeds in atmospheric waves

Abstract

A non-Doppler method for determining the horizontal speeds of point targets crossing a circular radar beam is presented. It requires knowledge of only the range, the relative signal intensity variation with time, and the beamwidth of the radar. With a high-range resolution FM-CW radar the errors in speed range from a few per cent to about ±20% depending on the time resolution of the signals. With a low-resolution pulsed radar the errors may be larger at short ranges but decrease rapidly with range. Speeds were measured with a vertical FM-CW radar with 2-meter range resolution. Dot angels, assumed to be insects, with observed 10-cm cross sections of 10−5 to 10−3 cm2 have speeds from 0.9 to 5.0 m sec−1. The high-range resolution also permits accurate determination of the target vertical velocities from the time derivative of their height. Vertical velocities range from −0.86 to +0.75 m sec−1. The variation in both vertical and horizontal speeds of a selected group of insects correlates very well with the simultaneously observed radar heights of an atmospheric wave at about the same altitude as the insects. On the basis of phasing difference it is concluded that the insects are moving opposite to the wave perturbation.