User guide

FS 20/25 Operators Manual 901-10037001/1.1

Theory of Operation Page 2.

Kongsberg Simrad Mesotech Ltd.

Port Coquitlam, BC - Canada

2. THEORY OF OPERATION

2.1 INTRODUCTION

This section explains the theory of operation of the Vertical and Horizontal Scanning

Trawl Monitoring Sonar System.

2.1.1 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 pulse

back toward the sonar transducer.

• The speed of the sound pulse projected through the water can be predicted for

given conditions.

2.1.2 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

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.

2.1.3 Forming an Image

The sound pulse projected will be attenuated as it travels through the water from the

transducer to the target and back. Much of this attenuation is a predictable function

of the total time or the distance the sound pulse traveled through water. Increasing

the receiving gain with time can compensate for this decrease in the signal level.

This is done automatically in the sonar with a Time Varying Gain circuit.