John Halsema
U. S. Navy, Submarine Base, Groton, CT 06349
John Irza
Sygnus Technology, Inc., Arlington, MA 02174
Traditional narrow-band synthetic aperture sonar (SAS) suffers from reduced along-track resolution and reduced pulse repetition as the speed of the sonar platform increases. Wideband SAS systems offer a method for reducing these undesirable effects at the expense of increased system complexity. Most recently, Gough and Hayes have demonstrated the performance of a wideband SAS that uses continuous-tone frequency modulation (CTFM) as the transmitted waveform [J. Acoust. Soc. Am. 86 (1989)]. This paper presents the system design for a wideband SAS that uses binary phase-shift keyed (BPSK) modulation for the transmitted waveform. In addition to being wideband (like CTFM), the BPSK signal offers unique advantages over CTFM in active SAS systems. In the system presented here, maximal-length pseudo-random (or pseudo-noise, PN) sequences are used to encode the BPSK waveform, offering the ability to transmit uniquely different coded waveforms in rapid succession, hence providing a higher spatial sampling rate than is achievable with uncoded waveforms. In addition to the system design, computer simulations are presented that compare images generated by narrow-band, CTFM, and PN-BPSK processing. Tradeoffs between image quality versus processing complexity are discussed.