Projects to locate small objects on the seafloor have traditionally utilized sidescan sonars operating at frequencies of 100 kHz to 500kHz. Performance of these units is limited by their short range and dependence upon target aspect to produce a satisfactory image. Sonars operating at lower frequency offer the advantages of detection at long ranges and less dependence upon target orientation. However, these systems have often been considered to lack the necessary resolution to image small objects. Through the optimization of towfish stability, ping rate, transmit pulse length, and system bandwidth, a total system resolution comparable to the higher frequency units has been achieved while retaining the long range capabilities of low frequency operation. The effects of the sonar operating parameters are discussed, field results of various small target searches are presented, data obtained at different frequencies are compared, and the implications for future operations are assessed.
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