Acquisition and analysis of migration data from the digitised display of a scanning entomological radar

Abstract

A scanning entomological radar was recently commissioned by the Institute of Plant Protection of the Chinese Academy of Agricultural Sciences for use in studies of the migratory flights of Heliothis armigera moths, and other insect pests of agriculture, in northern China. The radar differs from previous scanning entomological radars in its use of digitised rather than analogue signals in the production of a plan-position indicator (PPI) display. To enable efficient extraction of migration data from the radar observations, a secondary signal-processing system has been developed to acquire and analyse the display images. In this system, the VGA signal from the radar's digital PPI display is captured as either a single-frame or a multiple-frame bitmap. The secondary analysis then eliminates distortions and range rings, identifies insect dot-echoes, and generates a dataset of echo positions (three dimensions) and intensities. Analysis of mutiple-frame bitmaps additionally allows echo speeds and directions to be determined and ground-clutter echoes to be eliminated. Migration parameters for the overflying population—density, speed, direction, flux, collective orientation—and their variances are estimated from these datasets, and profiles of these quantities can be obtained by the usual scanning entomological radar technique of observing at a sequence of antenna elevations. This computer-based image-analysis technique has both efficiency and objectivity advantages over the film-based manual analyses previously used with this entomological radar configuration, and has proved effective in recent observations of H. armigera migration.