Modes for active and passive sonar testing explained

Scanmatic manufacture systems within underwater acoustics.  These systems are often used for testing and calibrating naval ship sonars, as well as training sonar operators, using modes for active or passive sonar testing.

What is the difference between active and passive sonar testing? A simplified explanation is that active sonar testing works like an echo repeater, i.e. it will return an echo for received sonar pulses in the water, while passive sonar testing simply emits sound or noise in the water. The following elaborate briefly for each of these test modes, that is supported by all Scanmatic systems for underwater acoustics, except those dedicated for underwater recording only.

Active sonar testing

The mode of active sonar testing is often referred to as Echo repeater. The system will return an acoustic echo for sonar pulses received in the water, with an operator-selected accurate time delay on the reflected acoustics, as well as additional optional effects. In this way it is possible to simulate the reflected sonar pulses from a submarine, naval mine, or similar underwater targets.

The time delay simulates the distance between the naval ship sonar and the underwater target (e.g. submarine). In addition, the operator can modify the reflected signal with additional effects such as Doppler shift, modified target strength level and add highlights. The Doppler shift simulates that the underwater target moves at a certain speed, while highlights use multiple echoes with varying target strength level to simulate variations in the physical shape of the underwater target.

It is also possible to use the mode variation Store repeater, which return a pre-recorded echo instead of the trigger pulse. This mode gives the facility of full output power with no “sing around” problems, thus considerable higher target strength may be achieved.

Passive sonar testing

In passive sonar testing, acoustic sound or noise is emitted in the water, and the signal source is most often an audio file or a signal generator. The signal will be transmitted either continuously (sub-mode: Noise passive) or at predefined intervals (sub-mode: Pulse passive). Settings are available for varying the transmit level in time – either increasing or decreasing, to simulate movement.

Examples of use for passive sonar testing:

  • Transmit wideband noise to simulate the signature sound of a naval vessel, for instance imitate the propeller noise to a specific type of submarine.
  • Simulate the sound of a torpedo attack.
  • Simulate “a target among other targets”.
  • Simulate sonar pulses from a ship-mounted active sonar, using pre-stored pulses that is transmitted at operator-selected intervals, optionally with varying level, increasing or decreasing in time, to simulate movement.