S. E. Forsythe
Underwater Sound Reference Detachment, Naval Res. Lab., P.O. Box 568337, Orlando, FL 32856-8337
Office of Naval Res., Arlington, VA 22217-5660
Narrow-band signals centered at frequencies from 600 Hz to 7 kHz were transmitted from a fixed projector to a fixed hydrophone array located 200 m away as part of the shallow water acoustic/geologic experiments at the New Jersey Atlantic Generating Station Site. Both the projector and hydrophone array were fixed 2 m off the ocean floor in roughly 15 m of water. The signals were Gaussian pulses 1 m in width modulated by weighted binary maximal length sequences (M-sequences). These M-sequences were designed to increase effective signal-to-noise ratio while retaining the time/space discrimination of the original Gaussian pulse. The pulse width was narrow enough to allow separation of component arrivals (e.g., direct and bottom reflection). A design method is presented that allows simultaneous control of frequency- and time-domain content of the transmitted signal. Examples of recovery of the transmitted signals and their multipath information are presented.