The measurement technique of bathymetry through sonar sounders has existed since the 1930s. Bathymetry is employed to measure the depth of ocean floors and the contour features of beds in other bodies of water. The technique of lake bathymetry, as the name suggests, relates to the measurement of bed depths over the body of a lake. By interpolating the sonar readings, it is possible to construct a three-dimensional (3-D) map of the lake floor showing contours and other bed features.
A body of water features a variety of ridges, troughs, and general depth contours, known as isobaths. Bathymetry is a study of these bed features, which is carried out utilizing either monobeam or multibeam echosounders. These echosounders emit beams of sound or light from the recording system to the bed of the water body. The depth of the water at that point is determined by the amount of time taken for the sound or light to return to the recording system. This technique is often referred to as sonar pinging.
A multibeam echosounder allows lake bathymetry surveys to be carried out in a far more effective manner than monobeam equipment. By emitting and recording an array of beams arranged in a fan pattern, multibeam echosounders can record a wider area and therefore require less passes. The fan arrangement of the beams also increases the accuracy of mapping very steep or vertical faces on the bed surface.
In terms of safety, lake bathymetry can be utilized to provide guidance for surface navigation. A further use, which is aimed more toward a hobbyist application, is studying a contour map to identify the best areas for fishing. These charts are known as bathymetric charts. An early tool used to establish bathymetric charts was a premeasured rope that was lowered over the side of a vessel. This original technique proved to be inaccurate due to the effects of underwater currents pulling the rope off center and was also a very time-consuming task, with only one depth measurement being taken at a time.
Modern lake bathymetry systems feature global positioning systems (GPSs) and altitude sensor equipment, which allow for adjustments to be made to compensate for the roll of the vessel on the surface. Global navigation satellite systems (GNSS) are also utilized in ocean bathymetry along with, to a lesser extent, satellite imagery. The technique of lake bathymetry is less common than ocean floor topography studies and is used mostly for vessel safety, recreational activities, and the study of mineral and rock deposits on the lake bed.