Echoes from Insects Processed Using Time Delayed Spectrometry (TDS)
TDS uses a linearly frequency modulated (FM) signal for system response analysis. The technique was first described by Heyser (1967) and has been applied to microwave and ultrasonic imaging systems (Heyser and LeCroissette 1974). Briefly, the technique utilized an FM probe signal where the instantaneous frequency of the signal received by the transducer is a function of the FM sweep rate and path length, or time delay, during transmission. Reflected signals (echoes) arriving at the transducer are delayed relative to the direct signal. Each time delay is associated with a frequency change hence the name, Time Delayed Spectrometry. TDS has several useful analytical aspects. For example, the nature of the probe signal allows for easy conversion between time and frequency domains. Also, one can show that, under certain restrictions, the echo is a (linear) FM signal modulated with the transfer function of the system (target). Hence the envelope of the echo is the numerical value of the transfer function for the target. If the phase information is available the impulse response can be obtained and the system can be uniquely described.
KeywordsFrequency Modulate Instantaneous Frequency Frequency Filter Linear Frequency Modulate Linear Frequency Modulate Signal
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- Heyser, R.C., 1967, Acoustical measurements by time delay spectrometry, J.Audio Eng.Soc., 15: 370–382.Google Scholar
- Schnitzler, H.-U., Henson, 0.W., Performance of airborne animal sonar systems: I. Microchiroptera, in: “Animal Sonar Systems,” R.G. Busnell, J.F. Fish, eds., Plenum Press, New York (1980).Google Scholar