Ventral-aspect radar cross sections and polarization patterns of insects at X band and their relation to size and form

V. A. Drakeab* http://orcid.org/0000-0001-9031-7906, J. W. Chapmanc http://orcid.org/0000-0002-7475-4441, K. S. Limd http://orcid.org/0000-0002-9166-2928, D. R. Reynoldsed http://orcid.org/0000-0001-8749-7491, J. R. Rileyde* & A. D. Smithde*a School of Physical, Environmental and Mathematical Sciences, UNSW Canberra, The University of New South Wales, Canberra, Australiab Institute for Applied Ecology, University of Canberra, Canberra, Australiac Centre for Ecology and Conservation, and Environment and Sustainability Unit, University of Exeter, Penryn, UKd Department of AgroEcology, Rothamsted Research, Harpenden, UKe Natural Resources Institute, University of Greenwich, Chatham, UKCONTACT V. A. Drake a.drake@adfa.edu.au School of PEMS, UNSW Canberra, PO Box 7916, Canberra BC 2610, Australia* Retired.ABSTRACTA data set of ventral-aspect insect radar cross-sections (RCSs) and polarization patterns, measured at X band (9.4 GHz, linear polarization) in laboratory rigs, has been collated from a number of sources. The data have been analysed to identify relationships between RCS parameters (one representing size and two the polarization-pattern shape) and the insects’ masses and morphological dimensions and forms. An improved mass-estimation relationship, with appropriate asymptotes for very small and very large insects, is presented. This relationship draws only on the RCS size parameter and it is shown that incorporating one or both of the RCS shape parameters provides little additional benefit. Small insects have polarization-pattern shapes that fall within a relatively limited region of the range of parameter values allowed by electromagnetic scattering theory. Larger insects have shapes that extend beyond this region, following a broad trajectory as size and mass increases; at masses above ~0.6 g, the pattern becomes ‘perpendicular’, with maxima when the E-field is orthogonal to the body axis rather than parallel to it. RCS shape can be used to infer morphological form for small insects (<80 mg), but not for larger ones. These results are consistent with observations from X-band vertical-beam entomological radars and provide a basis for identification, at least to broad taxon classes, of the targets detected by such radars.