Browsing by Author "Schaefer, G. W."
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Item Open Access The immediate extraction and display of insect flight trajectories from infra-red remote sensing signals(Cranfield University, 1982) Bent , Graham; Schaefer, G. W.The increasing need to study insect flight behaviour in the natural environment has led to the development of a relatively inex- pensive remote sensing instrument (IRADIT) . Flying insects dfferentay iumjmted, under a light cmations, in a intense ba of pulsed near infra-red radiation and detected using a gated image intensifier - CIV system at a rate of 5OHz. This thesis details the methods employed for extracting insect oo-ordinates from the' CI video signals, 'using low~oost electronic circuits ad micro computer (Apple II+) , and for the immediate analysis and display of two-dimensional insect flight trajectories, whilst rejecting environmental and system noise. Flight trajectories are often dominated by the immediate local wind. A new low-cost sensitive three dimensional digital anemometer system hs be developed for use with the IRADIT system, providing the data required to allow the vector wind to b immediately subtracted and interesting aspects of flight behaviour to b revealed. The IRADIT - Anemometer system ws tested i the field, on insects above wheat. _ Small insects with membzßanous wing areas as small as 5mm2 were readily detected and tracked over distances of the order of l at ranges up t 15m against a mid-day sky background. Subse- quent computer analysis of stored insect track and wind data oonfirmed that the effects of immediate local wind cn b smdied or canoelled out. Examples of insect flight behaviour are described. The relatively low cost of the IRADIT system and the practical features in its design result in a powerful new tool for use by the field entomologist.Item Open Access A quantification of the behaviourial dynamics of certain Lepidoptera in response to light(Cranfield University, 1984-08) Gaydecki, P. A.; Schaefer, G. W.Many types of insect, in particular the nocturnal Lepidoptera, will fly towards artificial sources of illumination. Such animals are often described as being positively phototactic, but although little progress has been made towards a fundamental understanding of this phenomenon, its existence continues to be exploited with the use of light-traps. This thesis attempts to explain, in part, why certain British night-flying Lepidoptera are caught, or fly close to, light-traps. The experimentation and analysis has been structured into three separate but inter-related studies. The first is an investigation into the effects that weather factors exert on light-trap catch. Standard analytical procedures were extended to reveal that sensitivity to these factors is related to insect size and gross morphology. The second of these studies is an analysis of the types of moth flight pattern produced when these insects are exposed to various forms of illumination under field conditions. Moth tracks were recorded on video with the help of image intensification, and the frame-by-frame co-ordinates transferred to, and processed by, a microcomputer, which produced matrix maps of speeds, accelerations and time-surface densities around a light-trap. Instantaneous windspeeds were recorded. The dynamical analysis suggests that moth flight towards light arises primarily from a misinterpretation of the stimulus, competing at short distances with a strong escape response, thus evoking a profound state of disorientation. Furthermore, the data indicated that the types of pattern found were species linked. In the third study, a remotesensing technique was used to quantify moth aerial density, which was compared with simultaneous light-trap catches nearby, giving an estimate of absolute trap catching efficiency under various meteorological conditions. Because of their mode of operation, and their increasing loss of effectiveness in higher windspeeds, light-traps have only a limited capacity to reflect aerial density.Item Open Access Quantification of the interactive motions of the atmospheric surface layer and a conifer canopy(Cranfield University, 1983-12) Scannell , B; Schaefer, G. W.Consideration is given to the use of.vane (DVA) and propeller anemometers in the sensing of atmospheric turbulence. Careful experimental measurements of the DVA dynamic response contributes to this consideration. Quantification of the airflow within and above a Sitka spruce canopy then follows. Statistics indicate the non-Gaussianity of the air turbulence Such forms are interpreted through the intermittency of turbulence and investigated by a conditional sampling scheme. Nindspeed spectra have ragged forms, showing them to be vastly modified by the combined effects of the canopy-imposed scales, together with the canopy's elemental vortex shedding frequencies and resonances. Studies of tree motions show the possibility of_a simple connection between the resonances of the separate canopy elements, which could provide the tree with an atmospheric shock-absorbing structure, supportive of its observed response to turbulence The ensuing proposal of a hypothetical qualitative mechanical design principle based on aeroelastic similaritynay bebeneficial to the tree's survivability in conditions of strong atmospheric turbulence.Item Open Access A Quantitative study of kite performance in natural wind with application to kite anemometry(Cranfield University, 1986-04) Hobbs, Stephen; Schaefer, G. W.Although kites have been around for hundreds of years and put to many uses, there has so far been no systematic study of their performance. This research attempts to fill this need, and considers particularly the performance of kite anemometers. An instrumented kite tether was designed and built to study kite performance. It measures line tension, inclination and azimuth at the ground, :sampling each variable at 5 or 10 Hz. The results are transmitted as a digital code and stored by microcomputer. Accurate anemometers are used simultaneously to measure the wind local to the kite, and the results are stored parallel with the tether data. As a necessary background to the experiments and analysis, existing kite information is collated, and simple models of the kite system are presented, along with a more detailed study of the kiteline and its influence on the kite system. A representative selection of single line kites has been flown from the tether in a variety of wind conditions. The results from these experiments are analysed to obtain general performance measurements for these kites in real, turbulent, winds. The analysis is taken a stage further to evaluate the kites for anemometry, and to study the dynamics of the kite system. The most suitable kites for anemometry are identified, together with the wind conditions in which they may be used and the wind information available from measurements at the tether. The study ends with a review, and a discussion of useful areas of further work. [This digital (pdf ) version of the thesis was created in August 2005. The content is identical to that of the original paper copy of 1986, although the layout and pagination differs in detail. Readers should note that anemometer calibrations described in Hobbs (1994) suggest that the windspeed values given in this thesis are incorrect by a few percent: however, the general conclusions about kite performance stated in the thesis are unaffected by these changes.]