Geodynamics - Services

Hydrographic surveys using multibeam sonar provide detailed information of the seafloor which are used for nautical charting, geological investigations as well as high-resolution data for various coastal engineering projects (to name just a few applications). The final product of swath-based bathymetric and backscatter surveys allow the end user to resolve features on the seafloor of varying size and frequency and to calculate a multitude of engineering parameters otherwise unattainable with single beam sonar.

Survey Vessel
The research vessel 4-Points is a custom fiberglass survey boat designed specifically for shallow water sonar and acoustical operations. The vessel is 25’ long with a 10’ beam; the bottom tapers from a deep “Carolina” style Vee to a relatively flat-bottomed stern that provides a shallow draft of approximately 1.2’. Twin 140 four-stroke engines, hung on a stainless steel bracket, power the vessel. All electronics and generators are grounded to the sea via a bottom mounted bonding plate to eliminate all potential electrical noise in the sonar data.

Multibeam Sonar Equipment
• Simrad EM 3000 multibeam sonar transducer
o Frequency: 300 kHz
o Max ping rate: 40 Hz
o No. of beams/ping: 127
o Beam width: 1.5o x 1.5o
o Beam spacing: 0.9o
o Depth range from sonar head: 1 to 150 m
o Depth resolution: 1 cm
o Depth accuracy: 5 cm RMS
o Range sampling rate: 15 kHz
o Bottom detection by phase or amplitude.
o Seabed imaging & classification with backscatter output.
o Full swath width accuracy to the latest IHO standard

• VT TSS Meridian Surveyor gyrocompass
o Settle point: 0.1o secant latitude
o Static accuracy: 0.05o RMS secant latitude
o Dynamic accuracy: 0.2o secant latitude
o Follow up speed: 200o /sec
o Settling time: <40 minutes to within 0.7o

• VT TSS DMS-10 motion sensor
o Dynamic heave accuracy: 5 cm
o Dynamic pitch & roll accuracy: 0.07o
o Output rate: 200 Hz

• Trimble 5700 dual frequency GPS system & RTK-Basestation
o Instrument used for positioning and tidal corrections
o High precision L1 and L2 measurements
o 24 channels L1 C/A code, L1/L2 full cycle carrier
o Extremely low latency (20 milliseconds)
o RTK-GPS accuracy depends on conditions such as multipath, obstructions, satellite geometry, atmospheric parameters and basestation control quality.
- Published horizontal accuracy: 10 mm + 1ppm RMS
- Published vertical accuracy: 20 mm + 1ppm RMS

• Odom Hydrographics Digibar Pro sound velocity probe
o Sampling rate: 10 Hz
o Depth accuracy: > 31 cm
o Velocity accuracy: +/- 0.3 m/sec

152 Hawthorne Drive - Pine Knoll Shores, North Carolina 28512 - 252-247-5785

Comments and questions are welcomed!
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