Mark Grabb
Ted Birdsall
Dept. of Elec. Eng. and Comput. Sci., Univ. of Michigan, 1301 Beal, Ann Arbor, MI 48109
Many oceanographic experiments and sonar systems require a short-duration, low-frequency, large bandwidth interrogation waveform for the purpose of obtaining precise travel-time measurements. The waveforms employed can typically be classified into three categories: short pulse, digital burst, or FM sweep (chirp). The FM sweep is the most flexible waveform class in that it can have arbitrary duration and amplitude while supplying desirable matched filter output properties (high resolution and low time-domain sidelobes). A design procedure has been developed to produce nonlinear FM burst waveforms that closely obtain a ``desired'' energy spectral density and hence matched filter output. A transmitter-to-receiver system analysis of the waveform has been conducted that includes a linear model of the transducer. The system analysis unveils the significant benefits of knowing the transducer characteristics precisely as well as uncovers the need for a transmitter clock rate that is significantly higher than the waveform's Nyquist rate. [Work supported by ONR-ASSERT.]