Vessel-Based, Shallow Water Mapping with a Phase-Measuring Sidescan Sonar

Coastal areas have traditionally been difficult locations to collect consistent, high-resolution bathymetric data via vessel-based acoustic surveys. The use of phase-measuring sidescan sonar is becoming more prevalent, particularly in shallow (< 20 m) coastal waters. Instruments used in the field over the last decade by the lead author are discussed here. This work is intended to serve as an introduction to the coastal scientist interested in the operation, use, and data sets associated with these instruments. Hydrographers unfamiliar with phase-measuring sidescan sonar will also benefit from insights regarding survey planning, data acquisition, and processing. These instruments collect co-located sidescan backscatter and swath bathymetry. The effective bathymetric swath widths can be 2 to 3 times that of multibeam echosounders making phase-measuring sidescan sonars ideal for shallow water mapping operations. These large effective swath widths offset the high levels of noise and processing needed in these bathymetric data sets relative to multibeam data. The sidescan backscatter and bathymetric data sets can be used individually, but the co-location allows for uses and analyses not feasible with other data sets. These instruments are well-suited to collect data for a suite of seafloor mapping projects and science-based investigations. Examples from a wide range of projects are detailed here for the shallow water mapping community and the multi-disciplinary groups who may benefit from the data and insights presented here.