Bathymetry and Acoustic Backscatter Data Collected in 2010 from Cat Island, Mississippi

• Abstract
• Introduction
• Survey Overview
• Data Acquisition
• Single-Beam Bathymetry
• Swath Bathymetry
• Backscatter/
  Side-Scan Sonar
• Data Processing
• Error Analysis
• Survey Products
• Data Downloads
• Logs
• Acronyms
• Acknowledgments
• References

DATA ACQUISITION – INTERFEROMETRIC SWATH BATHYMETRY

Differentially Corrected Navigation and Motion

OmniSTAR HP (High-Precision differential global navigation satellite system) was used for the swath bathymetry survey. OmniSTAR HP stated horizontal accuracy is +/- 10 centimeters (cm) and +/-15 cm vertically. The position data string was integrated in real time using the Coda Octopus F190R Precision Attitude and Positioning System, which includes a wetpod, or waterproof inertial measurement unit (IMU). In addition to the position string, the F190R records heave, roll, and pitch of the vessel during acquisition (table 3). Equipment offsets were entered into the F190 software prior to the survey.

Soundings

Interferometric swath bathymetry was collected aboard the RV G.K. Gilbert using a 468-kHz SEA (Systems Engineering and Assessment, Ltd.) SWATHplus-H sonar system (table 4). The transducers were pole mounted on the starboard side. The Coda Octopus F190R wetpod (IMU)(used for GPS and motion data) was mounted between the transducers (fig. 3). OmniSTAR HP position data and motion data were integrated with interferometric soundings in the SWATHplus software package (.sxs file), allowing for real-time-corrected depths. All equipment offsets were measured manually. Planned survey tracklines were entered in HYPACK for ship navigation.

Sound Velocity

A Valeport Mini Sound Velocity Sensor (mini SVS) was attached to the transducer mount and collected continuous speed of sound (SOS) measurements at the depth of the transducers. These values were directly read and incorporated into the SWATHplus acquisition software giving real-time speed of sound during acquisition (table 5). In addition, a separate sound velocity profiler (Valeport miniSVP) was used to collect speed of sound profiles (water surface to seafloor) throughout the survey (table 6). Correct SOS values throughout the water column are essential to accurately map the seafloor with a swath system. If the speed of sound is incorrect, refraction will cause erroneous depth measurements, which can increase the amount of manual post-survey processing.