MS48 hydrographic echo sounder analogue recorder made by Kelvin Hughes and used by the PLA hydrographic service to collect sonar data about the River Thames, British, 1970-1999.

Echo sounding is a type of sonar used to determine the depth of water by transmitting sound pulses into the water. The interval between emission and return of a pulse is recorded and used to determine the depth of water along with the speed of sound in water at the time. This is used for navigational purposes and to obtain information on water depths.

Starting in Jan 1976 the Royal Navy used the MS48 to survey the ocean floor as the new generation sounder for the Hydrographic Surveying Fleet The Port of London Authority used this echo sounder to survey the river bed to ensure accurate depth readings of the tidal River Thames. This provides vital information on depths and tides as well as marking any sunken obstructions Echo sounders were produced by Kelvin Hughes into the early 1980s, but manufacturing was eventually phased out to allow the business to concentrate on radar systems.