IMAGENEX DT101Xi, Technical Manual

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Doc no: 430-041-01 19 of 64
3.2.9. Background Graphics
Most navigation software allows for the loading of electronic navigational charts (ENCs). If used, ENCs
normally need to be purchased and loaded as an aid during survey. If ENCs are not to be used, it is
recommended to digitize and load the coastline and any navigation hazards that may exist in the survey area.
3.2.10. Time Synchronization
The DT101
Xi
and DT102
Xi
MBES have a well-designed and robust synchronization system that time stamps
all positional, attitude, heading and MBES systems via the supplied SIR unit. The PPS signal and NMEA
$GPZDA string for UTC (Coordinated Universal Time) are derived from the GNSS (GPS). This system
ensures highly accurate and synchronised timing for the application of auxiliary sensor data to the MBES
bathymetry.
The DT101
Xi
and DT102
Xi
provides a Transmit Sync Pulse to the SIR for accurate time stamping of each
ping. Sensor messages are time stamped and stored at their native update rates with a timestamp accuracy
of 100 microseconds. The navigation software then performs interpolation if required, and all sensors inputs
are calculated and logged for the correct instant in time. By convention, most software vendors log each input
at the times detailed in Table 3-1
Input Event Logged at
Heave Average of ping and receive time
Pitch Ping time
Roll Receive time
Heading Ping time
Position Ping time + 1-way travel time
Table 3-1
If there is a departure from the standard configuration, the Surveyor should ensure synchronization of all
sensors and equipment and ensure no latency exists. This is critical. Roll applied at an incorrect time
segment, for example, will lead to noticeable artefacts and a degradation in data quality. All PC clocks should
be set to the same time zone.
3.2.11. Survey Log
It is highly recommended that a comprehensive and detailed survey log be kept, either in handwritten or
electronic format. The format of such a log varies widely from operation to operation, but as a minimum, the
following should be included:
•
Make, model and serial numbers of equipment
•
Certification expiry dates
•
Software versions
•
Names of survey party members
•
Times, dates and locations of significant events
•
Static offsets (including a sketch)
•
Geodetic parameters
•
Tide stations (if used)
•
Patch test results
•
Start on line, end of line dates and times