The Echo Sounder

The echo sounder is an electrical device for measuring the depth of the water. It is now installed in almost every ship.

The principle of the measurement is as follows: the echo sounder sends a radio signal from below the ship to the seabed, where it is reflected back. The time taken to receive the reflected signal is a measure of the depth of the water under the ship. The radio pulse may be as short as 1 millisecond (thousandth of a second) and the frequency between 10 and 50 kilottertz (thousands of cycles a second). The received pulse is displayed on a chart by a pen recorder so that the navigator can see the outline of the bottom over which the vessel is passing.

An echo sounding apparatus consists of five basic components and operates as follows. Ultra-sonic oscillations are generated in the oscillation generator. These are of sufficient power to return echoes from several hundred fathoms. They are then supplied to the transmitting oscillator. The transmitting oscillator starts vibrating when the electrical oscillations are supplied to it, while the receiving oscillator, which is set vibrating by the echo, converts the mechanical vibration back into an electrical oscillation. The amplifier is used for strengthening the weak oscillations which the receiving oscillator has converted from sound vibrations. These oscillators can also be called transducers. The indicator or recorder measures and indicates the depth. Echo sounders can be divided into two kinds: recorders (echographs) and echometers. Echometres only indicate instantaneous depth, whereas echographs also record depths. If a vessel moves at a constant speed you can obtain an automatically recorded profile of the bottom of the sea along the route of the ship.