IMAGENEX DT101Xi, Technical Manual

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Doc no: 430-041-01 14 of 64
3.2.3. Vessel Dimensional Control / Shape File
Most navigation packages allow the user to input the size / shape of the vessel and define various points of
interest by means of a shape file. It is recommended that the Surveyor generates such a shape file as a
means of quality control and that during survey operations, the locations of, for example the MBES, GPS
antenna, etc., are shown on the nav screen. This also allows the coxswain of the vessel to have a refence
which will assist in keeping the MBES transducer nadir on the survey line.
3.2.4. Survey Line Generation
Most navigation packages allow the Surveyor to generate survey run-lines. Since the swath width projected
by the MBES is a function of water depth, swath angle, tilt angle, sound velocity, temperature, salinity, sea
state and bottom type, the width covered will vary through the survey and between surveys.
Note: Some software packages assess attained coverage in real time and adjust run-lines according to a
user defined coverage % parameter. In additions, some users may not pre-plan lines, but observe a coverage
plot within the MBES acquisition software, and decide on run-lines in real time. This method is clearly limited
to small survey areas and small vessels
The equation describing swath width is shown below (Eq 1):
𝑆𝑤 = 2. 𝑍. tan (
∆∅
2
)
(Eq 1)
Where
Sw = Swath width (m)
Z = Water depth (m)
ΔØ = Angular coverage (°)
The DT101
Xi
and DT102
Xi
have the option of dynamic roll correction (either through an integrated MRU if
fitted, or external MRU) through the sonar control software. In this configuration, beam steering is adjusted
as a function of roll. This allows the outer beams to be held parallel to the run-line and improve coverage
even during excessive roll. If this feature is
not enabled, consideration should be made to compensate for
shifting swath during excessive roll.
Through the Sonar Control Software, a sonar tilt angle of b/- 30° may be set. If such an angle is set,
consideration should be made when planning line spacing
It is recommended with a MBES system, to steer lines parallel to the mean depth contours. This will mean
that the depth variation along-track will be kept to a minimum and allow for robust planning of survey run-
lines as can be seen in Figure 3-6 Line spacing example [Manual on Hydrography]