| 摘要 |
A side-looking fish finding apparatus transmits a sonar pulse approximately horizontally into a body of water, and then monitors echoes from the pulse. The time interval between successive sonar pulses is varied in a random manner in order to permit two or more similar units to be used in close proximity to each other without significantly interfering with each other. An individual echo is treated as the detection of a fish if it has a magnitude above a predetermined threshold, if it has a length within a predetermined range bounded by upper and lower limits, if it is preceded by a leading space interval free of other echoes and having a predetermined duration, if it is followed by a trailing space interval free of other echoes and having a predetermined duration, the duration of the trailing space interval being less than the duration of the leading space interval, and if an equivalent echo is received in response to each of the next four successive sonar pulses.
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