Insect monitoring radar: stationary-beam operating mode

• Published in: Computers and electronics in agriculture Vol. 35; no. 2; pp. 111 - 137
• Main Authors: Drake, V.A, Harman, I.T, Wang, H.K
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2002
• Subjects: Chortoicetes; Echo modulation; Harmonic; Insect migration; Locust; Radar; Radar cross-section; Wingbeat frequency; Harmonic; Radar; Radar cross-section; Insect migration; Wingbeat frequency; Locust; Chortoicetes; Echo modulation
• ISSN: 0168-1699; 1872-7107
• DOI: 10.1016/S0168-1699(02)00014-5

Radars employing the zenith-pointing linear-polarised conical-scan (ZLC) configuration can be adapted to operate in a second mode in which the beam remains stationary and a time-series of echo intensity is recorded as a target traverses the beam. When the targets are insects, the intensity time-series incorporates a slow variation due to the traverse and usually also a modulation that arises from changes in the target's radar cross-section (RCS) due to its wingbeating. A number of target parameters can be retrieved from these time-series: the traverse speed, the wingbeat frequency, the depth of wingbeat modulation and the harmonic content. A lower limit on the target's RCS can also be set. Stationary-beam observations are now incorporated into the operating schedule of two ZLC-configuration insect monitoring radars (IMRs) deployed in inland eastern Australia and datasets of parameter retrievals are routinely produced for several thousand targets per night during periods of heavy migration. This paper describes the stationary-beam mode of IMR operation and presents an analysis of the results for 1 night of heavy migration when Australian plague locusts Chortoicetes terminifera are believed to have been the predominant target. Wingbeats were detected for over 68% of the 6631 echoes that were sufficiently strong to be selected for analysis, and strong and quite narrow peaks around 27–31 Hz, as expected for C. terminifera, were present in the frequency distributions. Harmonic incidence, modulation depth, target speed and the lower-limit of the RCS were also retrieved with good statistics. Speeds and RCS values were consistent with those from the night's conical-scan observations and, in the case of speed, may be somewhat more reliable. The distributions of most of these quantities varied somewhat with height, in some cases because of range-dependent factors in the radar's performance and in others probably because of differences in environmental conditions and/or the insects’ behaviours. The wingbeating parameters all appear to have the potential for discriminating between targets of different types and the results presented here indicate that an IMR can generate datasets of these parameters that are large enough for reliable inferences to be drawn from them.