Correlation Analysis of Echolocation Pulses
Following the lead of D. A. Cahlander (1967) and more recently of K. J. Beuter (this conference), radar ambiguity diagrams of bat pulses must now be regarded as an important extension to merely descriptive or acoustic analyses. The sonar properties of such signals are not intuitively obvious for several reasons: Their frequency and amplitude patterns differ from those of ‘worked examples’ given in radar texts and, indeed, often defy the engineers’ design constraints (eg. envelope shaping, unusual f.m. patterns and the presence of harmonics); such signals may be difficult to define for purely mathematical analysis. (2) Several of the assumptions of radar theory (or even under-water sonar theory) are not valid for ultrasound in air: the fact that bandwidth is large compared with the centre frequency means that Doppler shift must be treated as a factor (Cahlander) and not approximated by an incremental offset, so that for example, Doppler tolerance is achieved by linear period sweeps (Altes and Titlebaum, 1970), not by linear f.m. (3) Propagation attenuation in air is strongly dispersive, the atmosphere acting as a low-pass filter (Griffin, 1971), and this must affect many long-range ‘cruising’ pulses (Fig. 1).
KeywordsAttenuation Radar Sonar Altes
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