Kilohertz electro-optics for remote sensing of insect dispersal

Abstract: This thesis evaluates the possibilities of determining the flight direction of insects by analysing the wingbeat modulation pattern of the backscattered sunlight from insects. The Lund University Mobile Biosphere Observatory (LUMBO) was used during the summer of 2013 for a field campaign at two locations in Skåne, Sweden. The purpose of the campaigns was to study insect activity and biodiversity in the natural habitat of the insects, but also controlled insect releases were made. During controlled measurements of known insects, three dimensional flight trajectories were obtained by the use of a high-speed camera together with a strategically located mirror. Also the backscattered sunlight from insects was detected using two four-segmented photodiodes (Si and InGaAs) during dark-field measurements. In this thesis the photodiode data will play a central role. A simple model for the optical cross section (OCS) of an insect is introduced. It describes how the backscattered sunlight will be modulated depending on the angle of observation relative to the orientation of the insect. The signal is modulated with a fundamental frequency and its overtones, which are interpreted as the result of the wing motion of the insect. Assuming that the insects examined follows the wingbeat pattern described in the insect model, the harmonic frequency components of the modulated backscattered light are analyzed by studying their relative intensity, but also the phase difference between them. Three insect signals are examined and in two out of three cases there are some indications that the insect changes orientation during detection, and thereby, flight direction.