Zupt Inertial Survey Technology
Select a category to learn more:Technology Overview
Land Seismic Background
In many active geographical regions of land seismic exploration the canopy (trees/forestation) is such that RTK GPS cannot be used for the precise installation of survey stakes. The signals from the satellite segment of the GPS system cannot penetrate through to the receivers being carried by the field surveyors.
Global Positioning System (GPS) is based on satellites providing range data to a receiver at the location to be surveyed. We can reliably position a point today in an open space with GPS. We can accurately survey if we use Differential GPS – DGPS (1m to 2m). We can very precisely survey if we use Real Time Kinematic GPS – RTK (5cm to 15cm).
If we try and position using GPS in areas where the signals are masked or disturbed such as the urban setting seen right, we will degrade our positioning capability significantly.
If we were to try and position under trees (canopy) we can see that GPS will fail as the signals from the satellites are being masked (attenuated) by the trees.
If we combine the few GPS ranges we get with a good quality inertial unit we can maintain accurate survey grade positioning in these areas of poor (stand alone) GPS performance.
What we can also do is align the inertial unit to an installed monument and then position throughout the day just with the inertial unit. Alignment is maintained through the use of zero velocity updates (zupt’s) while surveying under canopy. When convenient, the unit is tied to a control point or survey monument and all data is re-processed to minimize errors.
This, although a very simplistic explanation, is how Zupt delivers very productive land survey positioning for seismic exploration.
Marine Construction – A basic introduction
Subsea precise positioning is achieved today through the use of Long Baseline (LBL) acoustic positioning systems (LBL provides relative accuracies of between 30cm to 3m depending on frequency). In a similar manner to GPS, ranges are measured to stations. In the case of LBL systems, multiple stations are deployed onto the seabed to provide the local coverage needed. These stations (transponders) are then calibrated (relatively [location with respect to each other] and absolutely [Lat, Lon and Depth]). Once calibrated the system is ready to be used for precise positioning. The type of work these arrays are used for is pipeline installation, sub sea manifold installation and general measurements during offshore oil and gas field construction. Remotely operated vehicles (ROV’s) are used today in the place of divers for deep water construction support. LBL systems are often used to position ROV during these tasks.
On the left we start to look at the example of a Remotely Operated Vehicle (ROV) involved in the installation of some subsea components (well-head, manifold, jumper, etc.) The ROV will be positioned with respect to this LBL array. To provide adequate coverage, positioning reliability and accuracy, a number of (usually 6 or more) transponders will be deployed and calibrated to form a LBL “array”. This “array” deployment and calibration will consume several “spread” days. The cost of this spread (vessel, ROV/personnel, survey equipment/personnel) will be in the region of $55K/day to $90K/day.
If we combine the measurements (observations) from just two transponders with a good inertial unit, pressure transducer and a velocity log we can provide the same positioning precision with much greater reliability. The spread time consumed to deploy these two beacons and calibrate them will be on the order of 30% to 40% of the time taken to deploy and calibrate the complete LBL array shown above. For each location Zupt’s services and equipment will shave between $100K and $200K off the overall cost of the operation. These oerations are ongoing throughout any deep water offshore field development.