Observing migrating insects with small special-purpose radars
Creators: name: Drake, VA
name: Hao, Z
Publisher: name: UNSW Sydney
Year: 2017

description: Entomologists studying insect flight and migration have made use of specially constructed radars for almost 50 years. These units are generally small in size, relatively low cost; they usually combine established, commercially available, radar and data-acquisition technology into configurations optimised for insect observations. Some units are mobile and can be deployed for short-term studies at locations where insect flights of particular interest are predicted to occur while others are permanently installed and monitor populations throughout the year. In all cases, operating schedules are determined exclusively by entomological priorities. Most of these radars operate at X-band (9.4 GHz) and are effective for observing larger insects (mainly grasshoppers and moths) but a few Ka-band (35 GHz) units for studying planthopper-sized targets have also been developed. These radars fall into two broad classes: scanning units that observe out to ~2 km and vertical-beam units that simply observe insects as they fly overhead. Both types provide profiles of insect activity to heights of over 1 km. The most sophisticated vertical-beam types can determine the speed, direction of movement, orientation direction, size, shape, and wing-beat frequency of individual insect targets, and accumulate statistics for these quantities for height and time intervals of order 100 m and 1 h respectively. However, the extreme range dependence of radar observations (inverse fourth power in the case of individual targets) makes profiler observations subject to major biases which require careful correction before variations of insect activity with height can be accurately portrayed. Observations with an X-band vertical-beam profiler in Australia have accumulated statistics on night-time locust and moth migration at an inland site over a 9-year period. Locust movements occur in late spring, summer, and autumn and are directed predominantly SW-ward in spring, N-ward in early summer, and broadly W-ward in autumn. Moth movements are particularly prevalent in early spring. Migratory flight occurs throughout the night and to altitudes of over 1 km. Wind estimates, obtained from reanalyses of weather observations using a regional-scale numerical model, show that insect migration is predominantly windborne. Nevertheless, the radar shows that moths and locusts exhibit a considerable degree of mutual orientation, and this is often at a significant angle to the wind. In some cases, locusts appear to be moving 'backwards' (or, rather, at &gt;90 deg from the direction in which they are heading). Radars of these types provide aero-ecological data complementary to the information obtainable from weather surveillance radars, and which appear potentially valuable for identifying the source of weather-radar reflectivity and interpreting the scans. Operating a small number of units at locations near a weather radar, and ideally alongside wind and temperature profilers and a particulate-detecting lidar (which will also detect small insects), appears a particularly attractive research-infrastructure objective for advancing aero-ecological research.
description: Radar Aeroecology Applications and Perspectives; Rome, Italy; 2017-02-23 - 2017-02-24