Basic Acoustic Theory
Echo sounding is the use of echosonars to determine the depth of water. Echosonars emit sound waves in a fan shape beneath a ship’s hull, then calculate the time amount of time it takes for the waves to bounce from the seabed and return to a receiver. This is how we map waterways and seabeds.
Multibeam surveys are used for collecting both bathymetry and acoustic backscatter information. They produce high-resolution coverage of wide swaths of the seabed more thoroughly and efficiently than single beam surveys. MBES systems are fast, accurate, and efficient, able to map multiple locations on the seabed with a single ping and with higher resolution.
Sonar Head Installation Guidelines
The Sonic 2024 sonar must be installed correctly for it to produce accurate data. The sonar head must be installed on a sturdy mounting arrangement. Any vibration or movement of the head, independent of vessel motion, will result in reduced swath coverage and noise in the data. Any installation (hull mount, moon pool, or over‐the‐side pole) must ensure the sonar head is in an area of laminar flow over the array.
In addition to the the 2024 model, the system requires a suite of ancillary sensors to provide complete and accurate survey data.
- Differential Global Positioning System Receiver
- Motion Sensor
- Sound Velocity Probe
In surveying, each component and sensor that produces information has its own reference point, unique to its position. When all sensors, (the sonar head, motion sensor, gyrocompass and GPS) have been permanently mounted, the physical offsets to a central reference point (CRP) must be measured.
Calibration: The Patch Test
A patch test is performed with each new installation or whenever a sensor is moved. The patch test involves collecting data over different bottom terrain to determine roll computation, latency, pitch, and yaw data.