| Pictures courtesy of Derek Mackay |
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| Pictures courtesy of Derek Mackay |
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Technical Specifications
SURFACE NAVIGATION 1 DGPS
MOD owns and operates Sercel NR103 and NR203 DGPS receivers
on the Veripos correction networks. The NR203 receivers have in-built multiref
capability either HF or RTCM inputs and has built into the firmware the UKOOA
DGPS QC facility.
SURFACE NAVIGATION 2 DGPS
MOD designed and owns the MODPoD system which is a stand alone
pod placed on the back deck of a tug for anchor positioning. The system is
completely self-contained and requires no technical knowledge from the tug
crew. Batteries in the pod allow for a minimum 72 hours of continuous use.
The pod contains and operates a Sercel DGPS receiver on the Veripos correction
network along with telemetry control.
PLATFORM POSITIONING 1
Accurig Software with EDM System(s) - MOD developed the Accurig
EDM system to meet the requirement for positioning jack-up rigs alongside
platforms. The system was accepted in May 1997 when Leica autotracking EDMs
were purchased although the software will function with up to 8 inputs that
may be ranges or bearings in any combination, i.e. Fan Beam Laser, RTK etc.
PLATFORM POSITIONING 2
Dual-frequency GPS Real-Time Kinematic (RTK) Positioning System
MOD utilize a Dual-Frequency Ashtech Z-12 Real-Time Kinematic GPS system for
use as an alternative to, or in conjunction with the Accurig EDM system for
the precise positioning of Jack-up rig's alongside platforms. Specified Accuracy's:
better than +/-0.1metre, system resolution 0.01metre relative to the platform.
Basic principle of operation: The system comprises two Ashtech Z-12 carrier-phase
dual-frequency GPS receivers plus two telemetry units. One GPS unit antenna
is located in a coordinated position on the platform offering good all-round
visibility to the GPS Satellite constellation. Precise coordinates of this
base GPS antenna position are input into the GPS receiver. The second GPS
antenna is located in a measured known point on the rig, also with good all-round
visibility. The telemetry system is set up for communication. Both GPS units
record simultaneous carrier-phase data from at least 5 common satellites,
with the base unit carrier-phase data and reference position being telemetred
across, input to and combined with the mobile rig GPS receiver data. By a
system of mathematical differencing computations, the precise bearing and
distance of the mobile GPS antenna relative to the base GPS antenna is calculated
and applied to the base GPS coordinates, thereby providing the mobile position
to a high order of accuracy.