Dual frequency single-beam sub-bottom profiler, 3.5kHz & 200kHz.

Dual frequency single-beam sub-bottom profiler, 3.5kHz & 200kHz.

Single-beam echo sounding – often referred to as “traditional SONAR” – has existed for more than 50 years. 

Confidence in the technology is often misplaced, however. There normally is no way to measure the orientation of a vessel-mounted transducer during single-beam SONAR operation, even if the vessel is equipped with a heave sensor, which limits the precision of this SONAR technology. The beam width of most single-beam sounders varies between 10 and 30 degrees, with the larger angles considered to be “broad beam.” 

The method utilized in single-broad-beam bottom detection relies on estimating the shortest slant range to the seafloor ensonified within the main lobe of the beam. As there is already an existing plus or minus 5 to 15 degree angular uncertainty (based upon the 10 to 30 degree beam-width), there is very little point in analyzing the vessel’s pitch and roll characteristics, as these are usually below this existing uncertainty. Thus, the method for determining the minimum slant range provides data that are merely an estimate.

While single-beam SONAR is reasonably adequate when the sea state is low and where the seafloor is reasonably flat, it has obvious limitations in accuracy and repeatability. Furthermore, even in ideal conditions, no information is gathered about the topography of the seafloor outside the SONAR beam footprint, which leads to guesswork about what lies between survey lines. 

See Side-Scan SONAR.