Bathymetry measures the depth and characteristics of bodies of water using echo sounders. Lake bathymetry creates 3D maps of lake beds using multi-beam fishfinders. It is used for navigation, fishing, and studying mineral deposits.
The technique of measuring bathymetry using echo sounders has been around since the 1930s. Bathymetry is used to measure the depth of the ocean floor and bed contour characteristics in other bodies of water. The lake bathymetry technique, as the name suggests, involves measuring the depth of the bottom on the body of a lake. By interpolating the sonar readings, a three-dimensional (3D) map of the lake bed can be constructed that shows the contours and other features of the bed.
A body of water has a variety of crests, troughs, and general contour lines, known as contour lines. Bathymetry is a study of these bed characteristics, which is done using monobeam or multibeam echosounders. These fishfinders emit sound or light beams from the recording system to the bed of the body of water. The depth of the water at that point is determined by the time it takes for sound or light to travel back to the recording system. This technique is often referred to as ping sonar.
A multi-beam echo sounder allows lake bathymetric surveys to be carried out much more effectively than single-beam equipment. By emitting and recording a series of fan-shaped beams, multi-beam fishfinders can record a larger area and therefore require fewer 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 used to provide guidance for surface navigation. A further use, more aimed at a hobbyist application, is the study of a contour map to identify the best areas for fishing. These charts are known as bathymetric charts. One of the first tools used to establish bathymetric charts was a pre-measured rope that was let down the side of a ship. This original technique proved inaccurate due to the effects of undersea currents moving the chord off the center and was also a time consuming operation, with only one depth measurement at a time.
Modern lake bathymetry systems are equipped with global positioning systems (GPS) and altitude sensor equipment, which allow adjustments to be made to compensate for vessel roll on the surface. Global Navigation Satellite Systems (GNSS) are also used in ocean bathymetry along with, to a lesser extent, satellite imagery. The lake bathymetry technique is less common than ocean floor topography studies and is used primarily for ship safety, recreation, and the study of mineral and rock deposits on the lake bed.
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