Single-beam sonar

The traditional single-beam echo-sounder (single-beam) consists of an underwater speaker and a microphone, built together in one unit.

The echo-sounder operates by sending a sound pulse to the seabed. Here it is reflected and returned. The time it takes the sound wave to travel down to the sea floor and back again, is an expression of the double depth of the seabed. The half-time is thus directly comparable with the current water depth.

Single-beam echo-sounder

Sonar is characterized by the frequency by which the sound wave is broadcasted. A low frequency gives a greater range but less resolution. Similarly, a high frequency gives a smaller range but a higher resolution. Typically used frequencies during hydrographic surveying in Danish waters are in the range of 200-400 kHz. In Greenlandic waters we mostly operate in the frequency range of 100 - 200 kHz.

Multibeam echo-sounder

Multibeam echo-sounder (multibeam) emits a sound wave in the transverse direction of the sailing direction up to 75 degrees to the vertical. This gives a complete coverage of the seabed equivalent to 3-7 times the water depth. A multibeam with a maximum opening angle of 120 ° will at water depths of 100 m on each survey line, be able to cover a corridor on the sea bed of (3.4 x 100 m) 340 m.

Multibeam is therefore much more efficient compared to the single-beam echo-sounder, especially if you want to make a hydrographic survey with 100% seabed coverage. Unlike the single-beam echo-sounder, that emits a single wide beam at the seabed, the multibeam is capable of receiving several separate beams. These beams (sound waves) are received in a fan-shaped pattern, enabling the system to collect depth profiles across the sailing direction.

Multibeam resolution

Multibeam is able to acquire up to 512 separate soundings in each depth profile. This provides a resolution that by far exceeds what you find by use of a single-beam echo-sounder. When surveying in 10 m of water the system will collect a sounding for every 7 cm across track (transverse to the sailing direction).