Reson SeaBat 7125 ROV, Operator'S Manual

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ACTIVE SONAR USAGE
SeaBat 7125 ROV Operator‟s Manual
Page 94 May 30, 2011
Version 3
6.4 Use of Displays
6.4.1 Equidistant versus Equiangular Beam Mode
RESON offer both equiangular (EA) and equidistant (ED) beam modes in the SeaBat
range of multibeam echosounders. In EA mode the beam center-center angular spacing
is constant across the swath and in ED mode the spacing is modified to maintain an
equal horizontal distance between soundings on the seafloor assuming a flat bottom. It
is recommended that this mode be used for general survey applications where the
requirement to achieve a specific number of sounding per cell in the across-track is
critical, or where the seafloor is generally flat.
In areas of significant relief and in particular when surveying features such as wrecks
and vertical structures such as harbor walls, EA mode should be used in preference to
ED mode. In extreme conditions, using ED mode over complex structures can cause
magnified artifacts due to the large overlap between beams towards the edge of the
sector.
For instructions on how to switch between the beam modes, see
section 3.3 Starting the
7k Control Center and Sonar .
6.4.2 Wedge versus B-Scan Display
The sonar wedge is the default view of the SeaBat sonar system. Change to B-scan
view when operating long distance. For further details on wedge and B-scan displays,
see
section 5.3 Primary Display Tab .
6.4.3 A-Scan, Phase and Magnitude Displays
With the A-scan displays it is possible to analyze the signal in a single beam (or group of
beams) to determine whether the bottom detection point is trustworthy.
The magnitude display is suitable to use for analysis of the middle beams and the phase
display is suitable to use for analysis of the outer beams of the swath. Signal Operator
Mode must be selected to make the phase display available (see
section 4.2.1 Data
Display & Format ).
For instructions on how to switch between the available A-scan displays, see
section
5.3.2.1 Available Displays .
6.5 Compensation for Environmental Conditions
As sound propagates through the underwater environment, the energy is absorbed by
the liquid caused by molecular interactions that convert acoustic energy into heat. A
propagating sound field also spreads geometrically, which means that the sound
pressure decreases with increasing distance from the sonar. Other mechanisms such as
bubbles, plankton, tidal currents, currents from rivers etc. may influence sound
propagation, but these mechanisms are difficult to measure and model, as they vary with
time and only appear in a limited number of areas. However, as absorption and