echosounding

Echosounding is a hydroacoustic technique for determining water depth and mapping the seafloor by transmitting a short sound pulse and recording the time until its echo returns from the bottom or from objects in the water column. Depth is calculated from the travel time and the speed of sound in water, which varies with temperature, salinity, and pressure.

A typical echosounder system includes a transducer, a pulse transmitter, a receiving system, and processing software that displays the results. Modern systems may use single-beam or multibeam configurations. Single-beam echosounders measure depth directly beneath the vessel, while multibeam echosounders emit a fan of beams to produce a wider swath of the seafloor and generate higher-resolution bathymetric maps.

Frequencies used in echosounding vary by application. Lower frequencies (roughly 12–30 kHz) travel longer distances and are common in deep water, whereas higher frequencies (up to 100–200 kHz or more) provide higher vertical resolution in shallow water but with shorter range. The choice of frequency affects penetration, resolution, and the quality of backscatter data used to infer bottom type and roughness.

Applications include nautical navigation safety, hydrographic surveying, coastline and port development, offshore engineering, marine geology, archaeology, and fisheries research. Outputs typically consist of depth profiles, bathymetric charts, and backscatter imagery.

Limitations and challenges include variability of the sound speed in the water column, water-column stratification, reverberation near the surface, multipath effects, and bottom return quality. Accurate data products rely on proper calibration, sound-speed casting, and correction algorithms to produce reliable depth measurements.