IMAGENEX DT101Xi, Technical Manual

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5. Operations
To cover all aspects and considerations is not possible due to the wide variety of environmental conditions,
job specifications, vehicle type and size, etc. The bullet points below represent some considerations to be
made during the data acquisition phase of the project:
•
It is highly recommended that during all data acquisition the Imagenex proprietary .IGX format file is
logged. In the Imagenex DT100 SIR software,
the user selects File > Record Start… and a file with
parameters determined by Setup > Automatic Filenames, Automatic Filename Type and Set
Maximum Filesize will be logged. These files may act as a diagnostic tool in the case of technical
issues, or as a back-up from which point and beam data (e.g. backscatter) may be extracted. The
IGX file may also be converted to a D1P format (via a utility in DT100 SIR) and in turn into an HSX
file via a Hypack utility. Since the IGX file logs only geographical coordinates (lat and long), the user
should be conscious of horizontal datum / geodesy and set the correct attributes during the
conversion to ensure no distortion of positional data occurs.
•
Latency, roll, pitch, and yaw corrections should be applied as per the patch test described in Section
4.2 and checked before commencement of any survey tasks.
•
SV cast at the start, upon completion and during the survey at appropriate intervals. The depth of the
cast should be appropriate to the survey depth; and at appropriate locations. (see Section 4.1).
•
Ray bending correction is disabled in the DT101
Xi
and DT102
Xi
and must therefore be applied either
in real-time during logging or afterwards during post processing by the MBES logging package.
•
Strategy for tidal correction should be defined and executed, including the possible use of external
tide gauges, RTK, etc. (see Section 3.2.7
– Datum Set-up).
•
The setting of a sounding grid cell size should be done (see Section 3.2.6).
•
Survey line spacing should be adequate to acquire sufficient coverage and data density. See (see
3.2.4).
•
Survey speed should be such that the sonar head is not subjected to excessive force, vibration or
induced noise and cavitation. (See Section 3.2.1).
•
Where possible, it is recommended to commence work in deeper water and work towards shallow
water. This is advantageous in terms of SV casts, as well as obstacle avoidance.
•
Constant monitoring of the navigation inputs should be undertaken. It is recommended to set up an
XY plot of the vessel position in the nav system and monitor any position jumps, navigation statistics
and additional data during data acquisition.
•
Gain and range should be adjusted so as to ensure good quality of data and depth determination
throughout. It is recommended that a real-time point-cloud be setup and monitored to ensure data
quality.
•
During data collection it is recommended that a waterfall display be opened in the MBES data
acquisition software so any SV anomalies will be detected. SV anomalies will manifest themselves
in ‘smiley’ or ‘frowny faces’ that are more pronounced at the edges of the swath and with deeper
water.
•
On a small vessel, it is recommended that movement of personnel be limited during data acquisition
to keep the patch test correction current. Periodic observations should be made of the draft marks
with respect to the mean sea level (Section 3.2.2)
•
Positioning, heading and attitude system should be monitored by means of time series plots, if
possible.
•
A comprehensive log should be kept at all times recording important settings, changes to any
settings, and a diary of events for use during processing.