Distinguishing target classes in observations from vertically pointing entomological radars

Abstract

Vertical-beam entomological radars incorporating rotating polarization and a very-narrow-angle conical scan generate information about both the trajectories of the insect targets and their identities. The identity information comprises four parameters, one a measure of target size, two of shape, and the last the wing-beat frequency. Transformations have been developed to convert these to a set of orthogonal variables that make the widths of peaks in the distributions similar. The existence of distinct target classes has been demonstrated from the radar observations themselves, using an 8-month data set. The analysis uses peak finding followed by association of the peaks found for different parameters, and is achieved through specially developed algorithms and procedures. Peaks have been identified in each parameter separately, in pairs of parameters, and in the four parameters together, the three approaches producing consistent results. Mainly single peaks were found in spring and the first month of summer, and also in late autumn, while multiple peaks occurred through most of summer and early autumn. All peaks are broad, so the number of target classes that can be resolved is not large. Classes were recognized by associating similar combinations of peak positions for the four parameters when these occurred on multiple nights. The most commonly occurring classes corresponded approximately to rules developed previously for identifying targets as locusts and moths. Two methods of using the identified classes to partition a target sample, with different purity-versus-yield trade-offs, are demonstrated.