Abstract
Entomological radars employing the ‘ZLC’ (zenith-pointing linear-polarized narrow-angle conical scan) configuration detect individual insects flying overhead and can retrieve information about a target’s trajectory (its direction and speed), the insect’s body alignment and four parameters that characterize the target itself: its radar cross section, two shape parameters and its wingbeat frequency. Criteria have previously been developed to distinguish Australian Plague Locusts Chortoicetes terminifera, large moths, medium moths and small insects using the target-character parameters. Combinations of target characters that occur frequently, known as target ‘classes’, have also been identified previously both through qualitative analyses and more objectively with a 4D peak-finding algorithm applied to a dataset spanning a single flight season. In this study, fourteen years of radar observations from Bourke, NSW (30.0392°S, 145.952°E, 107 m above MSL) have been used to test this approach and potentially improve its utility. We found that the previous criteria for assigning targets to classes require some modification, that classes identified in the previous studies were frequently present in other years and that two additional classes could be recognized. Additionally, by incorporating air-temperature information from a meteorological model, we have shown that different classes fly in different temperature ranges. By drawing on knowledge concerning migrant species found in the regional areas around the radar site, together with morphological measurements and radar cross-section data for proxy species, we have made tentative identifications of the insect taxa likely to be contributing to each class.
Highlights
Over the past five decades, there has been dramatic progress in the technical development of radar entomology and this has contributed greatly to developing an understanding of insect migratory behavior and its ecological consequences [1]
As well as accumulating research data, these two radars have played an operational role: the observations are routinely accessed by the Australian Plague Locust Commission (APLC) to support its decision-making and to recognize patterns in the development, spread and persistence of locust outbreaks [8]
The radar observations were recorded during three periods each of ~8 min every hour from 18:00 h to 06:00 h Australian Eastern Standard Time (AEST) every night and from eight height ranges at 150-m intervals between 175 and 1300 m
Summary
Over the past five decades, there has been dramatic progress in the technical development of radar entomology and this has contributed greatly to developing an understanding of insect migratory behavior and its ecological consequences [1]. Since the late 1990s, autonomously operating vertical-beam radars transmitting at X-band (9.4 GHz, 3.2 cm wavelength) and employing the ‘ZLC’ configuration (zenith-pointing linear-polarized narrow-angle conical scan) and known variously as VLRs (vertical-looking radars) and IMRs (insect monitoring radars), have been widely adopted [2,3] and this technology continues to develop [4]. In 1998, an IMR was installed at Bourke airport, New South Wales (30.0392◦S, 145.952◦E, 107 m above MSL) and has operated, with some gaps, up to the present. A second unit was operated at Thargomindah airport, Queensland (27.9864◦S, 143.811◦E, 132 m above MSL) from 1999–2013 [7]. As well as accumulating research data, these two radars have played an operational role: the observations are routinely accessed by the Australian Plague Locust Commission (APLC) to support its decision-making and to recognize patterns in the development, spread and persistence of locust outbreaks [8]
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