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The physics of bat echolocation: Signal processing techniques
1.This term was coined by Donald R. Griffin, an early researcher in the field of bat sonar. Echolocation refers to the ability of bats to orient themselves by using the echoes of sounds they produce.
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15.Some bats transmit a fundamental frequency plus at least one harmonic. Thus, the frequency-dependence of atmospheric attenuation may permit a crude range estimate from the received harmonic power ratio. We do not know if any bat species makes use of this technique.
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18.In the radar field, the electromagnetic equivalent of reverberation is called clutter.
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21.M. I. Skolnik, Introduction to Radar Systems (McGraw-Hill, New York, 1980), Chap. 10.
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25.We outline the steps in this calculation as follows. The bat estimates η from the power received in left and right ears: The echo power for constant SNR is proportional to receiver gain: assuming Here S is the target power received at range R, and N is the noise power. From this the error in estimating η, due to noise contaminating the signal, is determined. We substitute Δη into the right side of Eq. (7) and find Δθ as a function of θ. For realistic parameter values Δθ is insensitive to θ, as observed in Fig. 3. For a target of constant cross section, it is more realistic to hold the noise power constant than to say SNR is fixed, in which case In this case the SNR is a maximum at θ=0, and decreases as θ increases. So from Fig. 4 we see that Δθ increases with θ.
26.M. B. Fenton and G. P. Bell, “Recognition of species of insectivorous bats by their echolocation calls,” J. Mammal. 62, 233–243 (1981).
27.D. K. Barton, Radar Systems Analysis (Artech House, Dedham, MA, 1976), Chap. 3.
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30.W. E. O’Neill and N. Suga, “Encoding of target range and its representation in the auditory cortex of the mustached bat,” J. Neurosci. 2, 17–31 (1982).
31.This is in theory the best resolution that can be attained for a signal of bandwidth B. In practice many FM bat species get very close to this resolution.
32.B. Boashash, “Estimating and interpreting the instantaneous frequency of a signal—Part 1: Fundamentals,” Proc. IEEE 80, 520–538 (1992).
33.J. H. Fullard, “Predator and prey: life and death struggles,” Bats 9, 5–7 (1991).
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35.S. Schmidt, “Evidence for a spectral basis of texture perception in bat sonar,” Nature (London) 331, 617–619 (1988).
36.Thus, for the terminal phase resolutions of Sec. VII we find that, if the bat images what it sees in front of it to a range of 1 m, then it must process 350 000 resolution cells 200 times per second.
37.B. Boashash, “Estimating and interpreting the instantaneous frequency of a signal—Part 2: Algorithms and applications,” Proc. IEEE 80, 540–568 (1992);
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37.L. Cohen, in Time-Frequency Signal Analysis, edited by B. Boashash (Wiley, NY, 1992), pp. 3–42.
38.T. Collins and P. Atkins, “Non-linear frequency modulation chirps for active sonar,” IEE Proc. F, Radar Signal Process. 146, 312–316 (1999);
38.T. Collins and P. Atkins, “Doppler-sensitive active sonar pulse designs for reverberation processing,” IEE Proc. F, Radar Signal Process. 145, 347–353 (1998);
38.T. Collins and P. Atkins, “Doppler processing using comb spectrum transmission pulses,” Proc. Inst. Acoustics 20, 41–48 (1998).
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