Abstract: A method is provided for measuring the acoustic backscatter property of the floor of a body of water in which an acoustic multibeam echosounder employed on a ship is used to measure the sonic backscattered from a narrow transmission target strip on the sea floor that extends essentially vertically beneath the center of the transmitting antenna, transversely to the travel direction of the ship and which is successively exposed to sonic pulses by the transmitting apparatus. The measured backscatter is converted into sonic backscatter values allocated to receiving strips (115) of the multibeam echosounder. Calibration curves are constructed for all floor elements along the course line of the ship by echosounder measurements during a calibrating operation following a 90.degree. pivot of the echosounder around the vertical axis of the ship.

Abstract: Apparatus for use with a system in which successive pulses, each composed of a train of high frequency oscillations, are emitted by a transmitting transducer, propagated through a transmission medium, and received by a receiving transducer having a given transient behavior, the apparatus serving to measure the time interval between reception of successive pulses by the receiver transducer and to prevent erroneous measurements resulting from propagation of the pulses over indirect paths through the transmission medium, prevention of erroneous measurements being achieved by effecting time interval measurements only with respect to those pulses for which the output signal from the receiving transducer in response to reception of each such pulse exceeds a selected threshold value during a predetermined time interval subsequent to passage of that output signal above a given comparison value which is less than the threshold value.