Development of a Method for a Relative Backscatter Field Calibration using Reson 7125 Multibeam Sonar Systems

Acoustic backscatter measurements made by NOAA hydrographic multibeam systems are increasingly requested for use in seafloor characterization for other scientific applications. However, variability in backscatter measurements made by each of NOAA’s Reson 7125 multibeam sonar systems over the same area of seafloor is routinely observed and largely due to the fact that the systems are not calibrated. Such variability in junction areas of backscatter measurements made by separate systems results in poor mosaic quality and, in general, detracts from confidence in seafloor characterization efforts. A Reson 7125 SV1 multibeam sonar calibrated in the acoustic test tank at the University of New Hampshire in the spring of 2012 is currently in operation by NOAA ShipFairweather. The data from this calibrated system is being used in an attempt to develop an indirect method of determining backscatter measurement corrections for seven other un-calibrated systems currently in use by NOAA Ships Fairweather and Rainier. Acoustic backscatter measurements of a well known area of seafloor in Shilshole Bay, Puget Sound, WA, made over the last three years using eight Reson 7125s, including the calibrated system, are being used. Preliminary results of this research will be presented