1. Review Hardware Installation: Ensure that the two antennas remain fixed in place
relative to each other; otherwise there heading errors are present. Similarly, the position
of the primary antenna relative to the IMU should not change; such motion will cause
position errors in soundings.
2. Primary Antenna: Ensure that the primary antenna is closest to the IMU and connected
to the correct port.
3. Offsets: Measure offsets correctly to the nearest 1cm or better, and check that the signs
are correct.
4. Alignment: Ensure that the sonar (and IMU if separate) is closely aligned with the vessel
centerline (keel). Agreement to within ±0.5° is ideal if the sonar and IMU are within 5m
from one another.
5. Center of Rotation: If the IMU is not mounted at the CoR, it is important that the
processing software corrects for vertical motion using the CoR offset lever arm with roll
and/or pitch tilt as the heave sensor is less accurate than this. The heave should only be
used to determine the vertical displacement of the entire survey platform.
6. GNSS Corrections: Only Narrow Lane RTK is suitable for RTK tides. Position errors
increase with distance from the base station. DGNSS is accurate only to about 60cm
horizontally. Ideally use a post-processed kinematic solution. There are different options
depending on the GNSS equipment used during survey.
7. Surface Sound Speed: This may differ greatly in the upper 1m surface layer of the water
column. If this difference exists (check with a profiler) then, if possible, lower the sonar
below this layer boundary, but not so deep that the sonar pole cannot be controlled.
Generally, 1m is the limit. Compare surface sound speed from the WBMS with the sound
velocity profile at the draft depth. These speeds should agree within 1-2m/s.
8. Sound Speed Profiles: Should be taken as often as the changing conditions dictate. For
instance, once per day may be suitable in non-tidal areas of a river or lake while once
every 500m, or 1-2 hours, may be required for some regions where water temperatures
vary greatly.
9. Patch Test: Review multibeam roll, pitch, yaw and latency offset values. Repeat
measurements as and when required. Generally, during a single installation, roll should
not vary by more than ±0.02°, pitch by ±0.1° and heading by ±0.5°. Conduct a patch test
every time the sonar and IMU are moved.
10. Swath Angle: Bathymetric soundings are most accurate if they are within a ±70° area
from nadir (depending on water depth), or wider if the beam footprint and incidence angle
are very small, e.g. when the swath is perpendicular to a steep shoreline sloping up from
nadir. Soundings sloping down from nadir have a large footprint and incidence angle. It is
always better to ‘look’ up a slope than down one and therefore survey lines should
generally be parallel to the bottom contour.
9.8
Sonar System Diagnosis
In case of technical difficulties with the iWBMS system, users should refer to the guidelines below.
If possible, please have TeamViewer (or similar remote desktop control application of choice)
installed and ready to run, to allow NORBIT Support to control the system remotely. This
section explains how to diagnose sonar-related issues, while the following section discusses
Applanix-related problems.
In case the sonar starts to function erratically, NORBIT support will advise the user to perform
diagnostic checks, including, but not limited to the following:
1. Verify IP Address of Acquisition/Control PC: Should be 192.168.53.XXX, with XXX
being greater than 100 and less than 255. The system subnet mask should be
255.255.255.0.
2. Verify Power Supply: If WBMS GUI fails to connect to or detect hardware, first check if
the system is powered on. If so, check the power supply voltage with a voltmeter. Also,
To Next Page
Loading...
