. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECHOLOCATION OF FLYING INSECTS 485 echo in a linear detector. It would achieve an improvement in signal: noise ratio because it could compare the returning- echo with a reference frequency. Such a system would require closely controlled frequency constancy or the beginning of echo detection would he uncertain by a number of wave-lengths. In addition, relative movement of bat and target introduces complications—chiefly 1 )oppler shift. Doppler shift could, indeed, be the quantity assessed in these 20 msec., giving a measure o
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ECHOLOCATION OF FLYING INSECTS 485 echo in a linear detector. It would achieve an improvement in signal: noise ratio because it could compare the returning- echo with a reference frequency. Such a system would require closely controlled frequency constancy or the beginning of echo detection would he uncertain by a number of wave-lengths. In addition, relative movement of bat and target introduces complications—chiefly 1 )oppler shift. Doppler shift could, indeed, be the quantity assessed in these 20 msec., giving a measure of the relative speed of the target. What the effect or role of the slight frequency rise at the beginning of the pulse and. therefore, at the be- ginning of the echo would be cannot be formulated now. Nor can we yet ex- tensively interpret the role of the terminal frequency drop. 60 50 40 o 30 o 0> LO - 20 0. 0 Meters FIGURE 4. One example of a ('. f>tinicllii pursuit of a t'ruit fly. Tin- duration of the silent period between pulses is plotted against the calculated distance from the target at the beginning of the pulse preceding each interval. Distance can he reconverted to time. m. — 1 sec. Second, the pulse and the echo could be heterodyned in the ear ( Wever and Lawrence, 1954). Since there is relative motion between bat and insect the echo is Doppler-shifted and the synthesi/.ed signal contains stun and difference fre- quency components in addition to the pulse and echo frequencies. The difference frequency may be viewed as a relatively slow amplitude modulation of a basic signal: with a closing speed of 5 , and an output pulse frequency of 34 kc this modulation frequency would be about 1 kc. The onset of the modula- tions would give the target distance (by elapsed time) and the frequency of these modulations would give the closing speed. This method should be useful if the ratio of perceived outgoing signal/reflection were between 0.
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
