Using the ST725 sonar for AUV feature based navigation and correction

This paper reports on a previous experimental investigation of the Tritech ST725 high resolution sonar system used onboard the NPS Phoenix and a possible extension of the results to an underwater feature based navigation and correction system. The ST725 sonar was used in progressively complex static environments to clearly image objects. Scanline analysis of the ST725 data was conducted and shown to be useful in extracting stationary target information on vertically oriented mine-like objects as well as a small sphere. Raw scanline processing using a "gating and thresholding" method was used to determine range, bearing, and approximate size/orientation. Additionally, by capturing the range of the first return, the sonar was shown to be capable of emulating a "profiling" sonar. Future synthesis of known underwater features with range and bearing information and scanline analysis may provide the underwater vehicle systems designer with an alternate method of navigation. The value of this topic in the advancement of understanding underwater technology is that actual experimental data were used and useful results were obtained.