What is « Interferometric sonar » ?
A swath-sounding sonar system is used to measure the depth in a line extending outward from the sonar transducer. As the survey vessel moves along a trackline, the swath transducer sends out sonar signals at a right angles to the trackline and is scanning the seabed to each side of the vessel. It sweeps out an area of depth measurements, referred to as a swath. The word interferometric refers to the technique used to measure soundings. The interferometric technique uses the phase content of the sonar signal to measure the wave front that is returned from the seafloor or other targets such as a seawall.
(Source : USGS)
What is « Multibeam echosounder » ?
A multibeam echosounder is a type of sonar that is used to map the seabed. Like other sonar systems, multibeam systems emit sound waves in a fan shape beneath a ship’s hull. The amount of time it takes for the sound waves to bounce off the seabed and return to a receiver is used to determine water depth. Unlike other sonars, multibeam systems use beamforming to extract directional information from the returning soundwaves, producing a swath of depth readings from a single ping.
(Source : Wikipedia)
What the difference between inteferometric sonar and a beamformer sonar ?
Interferometers and beam-forming multibeams are different tools in the surveyor’s toolkit; each of them is the better choice for certain kinds of task. In general, interferometer are better for shallow water (less than 100 metres depth), where the wide swath width gets the survey done faster. Conversely, beamformers tend to have a greater depth range for the same size of sensor. Some survey organizations use both kinds of instrument, and use them together or select the best one for each task.
RANGE AND ANGLE MEASUREMENT
Both interferometric multibeams and beamforming multibeams measure range and angle to a series of points on the sea bed. A beamformer mathematically forms a set of “beams”, and detects the range to the sea bed in each beam. An interferometer measures the angle the incoming sound wave fronts in a time sequence of samples. Slant range is obtained from the time of the sample and speed of sound. In summary, beamformers measure range for each of a set of angles, and interferometers measure angle for each of a set of ranges.
ADVANTAGES OF INTERFEROMETERS
Wide Swath Width
An interferometer produces a swath width of 10 to 15 times water depth, depending on sonar conditions. This advantage is particularly clear in shallow water (less than 30 m).
What are we talking about when we say …?
USV= Unmanned Surface Vehicle
AUV= Autonomous Underwater Vehicle
ROV= Remotely Operated Vehicle
SU= Subsea unit
DU= Deck unit
PSM = Permanent Siltation Monitoring
GNSS= Global Navigation Satellite System
SVS= Sound Velocity Sensor
TEM= Transducer Electronic Module
MBES= Multibeam Echosounder
DTM= Digital Terrain Model
DEM= Digital Elevation Model