IMAGENEX DT101Xi, Technical Manual

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The footprint on the seabed approximates an ellipse with semi-minor axis = ct (Eq 4) and semi-major axis =
lt (Eq 7). The semi-minor axis is the axis of interest as the long-track direction will be saturated with scans if
the correct survey speed is achieved (See Section 3.2.5 Ping Rate and Survey Speed). Since the sounding
grid is square, and not elliptical, a factor of 0.5 is recommended to reduce the square size to a square
inscribed by the ellipse (as shown in Figure 3-8 Square Inscribed by Ellipse)
Figure 3-8 Square Inscribed by Ellipse
The equation to approximate sounding grid size is therefore:
𝑆𝑜𝑢𝑛𝑑𝑖𝑛𝑔 𝐺𝑟𝑖𝑑 𝑆𝑖𝑧𝑒 = 𝑐𝑡 × 0.5
(Eq 10)
Where
ct = cross-track size (Eq 4)
3.2.7. Datum Set-up
Both the vertical (tide) and horizontal (geodetic) datums should be defined and set-up in the navigation
software. If a tide gauge is used to measure tide, it should be set to work prior to the commencement of the
operation. If predicted tide is to be used, the appropriate tide tables / predictions should be sourced in
anticipation of the survey. Tide files should be at the appropriate density to reflect the tidal regime in question.
High accuracy GPS such as RTK may also be used for tide measurement and the preparation for this should
be done in the appropriate software.
3.2.8. Navigation
There are many options to improve the quality and accuracy of GNSS. These include Differential GPS
(DGPS), Wide Area DGPS, RTN and RTK. There are many options for the reception of correction messages
associated with these systems including satellite, radio modems and GSM networks. Preparations for the
transmission and testing of these services should be completed during mobilization.
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Inscribed square
Elliptical footprint