02-05-2011, 04:32 PM
ABOUT YOUR SONAR
TERMINOLOGY:
The following is an explanation of the basic terms used by Imagenex to describe their sonar
techniques.
Color: The different colors used to represent the varying echo return strengths.
Echo: The reflected sound wave
Echo Return: The time required for the echo to return to the source of the sound
Sonar: The principle used to measure the distance between a source and a reflector (target)
based on the echo return time
Target: The object that you wish to obtain information about.
IMAGING: Fan shaped beam
Scans surfaces at shallow angles, usually through a horizontal angle
Displays color images or pictures
Complete echo strength information for each point
Primarily for visual interpretation
In Imaging a fan-shaped sonar beam scans a given area, by either rotating or moving in a
straight line, through a series of small steps, (see Figure 1). The beam's movement through the
water generates points that form a sonar image of the given area. The different colored points,
representing the time (or slant range) of each echo return, plot a line on a video display screen.
The image, consisting of the different colored lines, depicts the various echo return strengths.
The following characteristics are necessary to produce a visual or video image of the sonar
image:
! the angle through which the beam is moved is small
! the fan-shaped beam has a narrow angle
! the transmitted pulse is short
! the echo return information is accurately treated
These visual images provide the viewer with enough data to draw conclusions about the
environment being scanned. The operator should be able to recognize sizes, shapes and surface
reflecting characteristics of the chosen target. The primary purpose of the imaging sonar is as a
viewing tool.
PROFILING: Narrow pencil shaped beams
Scans surfaces at a steep angle usually on a vertical plane
Displays individual points or lines
Accurately cross-sections a surface
Echo strength for each point higher than a set threshold
Digitizes a data set for interfacing with external devices
Data set is small enough to be manipulated in a small computer
Primarily a measurement tool
In Profiling a narrow pencil-shaped sonar beam scans across the surface of a given area
generating a single profile line on the display monitor, (see Figure 2). This line, consisting of a
few thousand points, accurately describes the cross-section of the targeted area. A key to the
Profiling process is the selection of the echo returns for plotting. The sonar selects the echo
returns, typically one or two returns for each "shot", based on a given criterion for the echo return
strength and the minimum profiling range. The information gathered from the selection criteria
forms a data set containing the range and bearing figures. An external device, such as a
personal computer or data logger, accesses the data set through an RS-232 interface with the
sonar.
The profile data is useful for making pen plots of bottom profiles, trench profiles, internal and
external pipeline profiles. The primary purpose of the profiling sonar is as a quantitative
measuring tool.
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