A New Application of Echo-Sounding

Abstract

BY 1937 the biological researches at Wray Castle had reached the stage when a detailed bathymetrie survey of Windermere was desirable as a basis for studying features of the lake bed. The Hydrographer to the Admiralty kindly agreed to co-operate on the technical side, and a survey was carried out by Lieut.-Commander Farquharson, of the Admiralty's hydrographic staff, using a magneto-striction recording echo-sounding machine of Admiralty pattern manufactured by Messrs. Henry Hughes and Son, Ltd. The main feature of the recorder (Fig. 1) is a drum which is rotated at a constant speed by an electric motor. An arm attached to the drum carries a metal 'pen' which traces the record on paper moistened with solution of potassium iodide and propelled slowly through the machine. Contacts on the drum are arranged in such a manner that a supersonic sound impulse is transmitted from an oscillator, below the surface of the water, for an instant when the revolving pen has just begun its transit across the paper. The sound impulse, directed downward, is reflected from the bottom, is picked up by a receiving oscillator also mounted in the water, is amplified and passed to the pen. The rises in voltage at the pen point, consequent on the transmission and return of the signal, cause electrolysis of the potassium iodide and produce brown stains of iodine on the paper—one, the zero mark, at the instant of transmission, and the second on the reception of the echo. The distance along the are of the pen's track between these two marks represents the depth of water, and the process, repeated at each revolution of the drum, gives a continuous record of depth. The whole equipment, consisting of the recorder, amplifier, oscillators and 12-volt accumulator, can be mounted comfortably in a small launch or rowing boat.