VESSEL-BASED ACOUSTIC MAPPING OF INTERTIDAL ZONES IN MICROTIDAL AND MESOTIDAL ENVIRONMENTS: INCREASING EFFICIENCIES AND REDUCING UNCERTAINTIES WITH PHASE-MEASURING SIDESCAN SONARS

Traditional sidescan sonars have long been used in intertidal areas, but vessel-based, swath bathymetry data have been sparse due to the low swath width to depth ratios attainable with multi-beam echo-sounders (MBES). Often airborne lidar data are used but those data are less frequently collected and can have temporal and spatial offsets that make the data less useful. Terrestrial lidar scanners are becoming more prevalent, but they require set-up and removal for each area scanned and typically cover less area than a high-tide, vessel-based sidescan sonar survey. Further, those elevation data (bathymetry or lidar) then have to be co-located to the extent possible with the sidescan data and this can be difficult and introduces more uncertainty.

Phase-measuring sidescan sonars provide co-located swath bathymetry and high-frequency sidescan sonar imagery from a single, vessel-mounted instrument. Data can be collected using RTK-GPS providing the highest level of positional accuracy to both datasets. The swath width to depth ratios are 2-3 times greater than MBES allowing for more cost-effective surveys and less time in hazardous shallow water areas. Phase-measuring sidescan sonars do have drawbacks in terms of large, noisy datasets but these are improving with continuing evolution of sonars and software.