Measuring depths with echosounders and sonars
1 - 2,000 soundings per survey
500,000 - 750,000 soundings per survey
4,000,000 - 100,000,000 soundings per survey
An echosounder sends sound pulses through water to measure water depth. The water’s depth is calculated by recording the time between the emission of the sound and the reception of an echo as well as the speed at which the sound travels through water. The echosounder first was developed for military purposes, but by the mid-1930s it was used widely for hydrography in Canada.
Early echosounders were quite crude and had low resolution (large sonar footprint). They ...view middle of the document...
Fortunately, the single-beam echosounder and sidescan sonar are complementary.
Another approach used by CHS is the sweep system, which deploys many single-beam echosounders (SBES) equally spaced along a boom, or some booms, of a vessel. The sweep system provides total coverage of the seabed, at least at some depths, while still acquiring precise depth and position of each measured sounding.
CHS uses the Canadian Coast Guard’s F.C.G. Smith, which has single-beam echosounders lined along its booms in a sweep system.
This approach, however, has some constraints. The operation of large booms is awkward and restricts the manoeuvrability of a ship. While the sweep system has a far larger coverage range than the single-beam echosounder, it is still limited by the width of the ship’s booms.
The swath system represents that class of sonars that can obtain multiple across-track soundings from the same array of transducers—usually a transmitter array and at least one receiver array. A swath system does not have the physical constraints of a sweep system. And its angular coverage of the seabed makes it far more efficient than a sweep system as the depth increases.
Multibeam echosounders (MBES) are one class of swath system. Like single-beam echosounders (SBES), they transmit a shaped acoustic pulse into the water column. Unlike SBES, the transmit beam (or ping) is very wide in the across-track direction and very narrow in the along-track direction. The receive beams—and there are many receive beams for each ping—are very narrow in the across-track direction and somewhat wider in the along-track direction. The combination of these two beam patterns results in wide coverage across-track with very high spatial resolution. This system overcomes all the shortcomings of combined single-beam echosounders and sidescan sonars, as well as the limitations of sweep...