Hydrographic Survey

Multibeam sonar systems provide highly accurate bathymetry charts. Their accuracy is dependent on several factors.

  • Knowing the position of the transducer head relative to the earth, vertically and horizontally. This data is a starting point for the acoustic pulse.
  • Knowing the pitch, roll and yaw angles of the transducers head. This data gives a start and finish orientation for the transducer head.
  • Knowing the sound speed at the transducer head. This allows the determination of the arrival angles of the various beams relative to the transducer head.
  • Knowing the sound speed profile from the transducer head to the sea floor. This allows the sonar processor to calculate range and to correct for refraction (bending) of the acoustic beams.

AML Oceanographic instruments and sensors are used to correct the latter two sources of multibeam error.

The Importance of Sound Velocity

Knowledge of the ambient sound speed conditions is one of the most critical and universal sources of error in underwater acoustics.

Sea Surface Sound Velocity

A sound speed sensor should be mounted at the multibeam transducer head and sampled with every ping of the multibeam sonar. Why?

Vertical Profiling

The path the acoustic wave takes from the transducer to the seafloor is determined by a multitude of factors. Sound speed profiles are therefore required to process multibeam sonar data.

SV vs. CTD

Sound velocity can be measured directly using a sound velocimeter or it can be calculated from salinity, temperature, and depth measurements, assuming standard ocean salt ratios. AML invented time-of-flight sound velocity measurement.

Benefits of Underway Profiling

By enabling high speed, deep water underway profiling, the MVP economizes survey operations while enhancing performance.

How Often Should Sound Velocity be Measured?

For accurate sound speed data, measurements should be made close to the acoustic system both, spatially and temporally. Spatial and temporal requirements vary by application, location, and contract.

Hydrographic Survey Products

Photo courtesy of NOAA
IMG_5850 NAVO Bowditch
Photo courtesy of NAVO