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Acoustic Multi Beam Survey Systems for Deep Draft Navigation Projects


Quiz Questions

1.___________________systems can also be configured for waters-edge to waters-edge coverage (i.e., over 180 degree swath), allowing side-looking, full-coverage underwater topographic mapping of constricted channels, lock chambers, revetments, breakwaters, and other underwater structures.
Multi-beam
Single-beam
2.Swath systems are typically designed with between_________________ beam spacing.
0.5 deg and 3.0 deg
1.5 deg and 3.5 deg
3.Multi-beam sonar’s bottom detection thus provides three pieces of information: (1) the angle of the beam along which the acoustic pulse traveled, relative to the sonar head, (2) the round-trip travel time of the acoustic pulse, and (3) a signal intensity time series of the bottom return.
True
False
4.Horizontal positioning accuracy is not dependent upon the ability of the system to compensate for pointing errors caused by vessel roll, pitch, and yaw (Figure 11-3).
True
False
5.As with single beam echo sounders, the smaller the beam angle, the better the system is able to discern true depth and resolve small features.
True
False
6.The electronic beam formed echo sounders use a common fan beam projector and an array of polymer receive elements physically pointed in the desired direction.
True
False
7.Beam direction is determined by measuring differences in signal arrival times on an array of receive elements (phase differentiation).
True
False
8.Multibeam systems are an effective quality control process on dredging projects requiring 100% bottom coverage to assess and certify project clearance.
True
False
9.Multibeam systems are not recommended for payment or clearance use on shallow-draft projects.
True
False
10.Multibeam sensors cannot be configured to detail pipelines, bulkheads, flood walls, lock walls, revetments, breakwater riprap, and other similar underwater structures.
True
False
11.Multibeam survey systems represent an effective mechanism for detection of shoals, rocks, wrecks, debris, or other navigation hazards lying above grade in a navigation channel.
True
False
12.Multiple-transducer, boom-mounted, channel sweep systems are generally preferred for use over multibeam survey systems in shallow-draft (<15 to 20 feet), sand/silt-bottomed navigation channels.
True
False
13.Multibeam systems are normally ______________ utilized on small, mobile survey vessels up to 26 feet in length, with the transducer assembly externally mounted over the side.
More cost-effectively
Less cost-effectively
14.Alignment and offset parameters must be measured for the various sensors making up the multibeam system, e.g., gyro alignment/offsets, transducer mounting angles/offsets, DGPS antenna offsets, static and dynamic drafts, vessel settlement/squat, and estimated latencies.
True
False
15.A performance test is not a quasi-independent test which is not used to assess the quality of data being collected and to verify conformance with the prescribed accuracy specification or object detection requirements for the project.
True
False
16.Static offsets of the sensors are the distances between the sensors and the reference point of the vessel or the positioning antenna.
True
False
17._______________ is the depth of the transducer head below the waterline of the vessel.
Transducer draft
Transducer offset
18.The multibeam transducer should not be installed near to the centerline of the vessel and level about the roll axis.
True
False
19.The__________ should be aligned with the x-axis of the vessel using an electronic total station and geodetic control points.
Gyro
Squat
20.Time delay in the positioning is the ______________ between the time positioning data are received and the time the computed position reaches the logging module.
Time lag
Time lead
21.Patch tests are periodically performed to quantify any residual biases in the initial alignment measurements described previously.
True
False
22.The maximum speed may be calculated by the following equation:
v = S • d • tan (b/2)
where sounder sampling rate per second is denoted by ____.
S
b
23.The following equation a = tan -1 [( da / 2 ) / (depth) ] denotes ___________.
Pitch offset
Along-track displacement
Water depth
24.The following equation y = sin -1 [ ( da /2 ) / XI ] denotes
Azimuthal offset
Relative across track distance
25.The roll offset can be estimated by the following equation: r = tan -1 [ ( dz / da ) / 2 ]. This equation is for ____________.
Small angles of less than 2 deg
Small angles of less than 3 deg