Unit installation

FS70 Trawl Sonar System
8 974-24007001/4.1
2 THEORY OF OPERATION
2.1 Introduction
This section explains the theory of operation of the Vertical and
Sounder Scanning Trawl Monitoring Sonar System.
2.2 Basic Principles
Sound waves travel very efficiently through water.
A sound pulse can be projected through water in a controlled
direction with the sonar transducer.
An object in the path of the projected sound pulse will reflect some
sound pulses back toward the sonar transducer.
The speed of the sound pulse projected through the water can be
predicted for given conditions.
2.3 Determining Target Position
The trawl scanning sonar processor measures the time from the start
of the sound pulse projected through water, to the reception of the
sound pulse reflected back to the sonar transducer. The measured
time is then converted to distance by using the value of sound speed
through water.
Since the sound pulse is projected in a known direction, the bearing
of the reflected object is also known. This makes it possible to
locate the object with respect to the sonar transducer; the
information will be used to plot the position of the reflected target
on a video graphic display monitor.