Velocity

2013

NovAtel's Annual Journal of GNSS Technology Solutions and Innovation

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ACES/geophones " The NovAtel solution was environmentally much more acceptable for people who were doing oil and gas surveys, and it saved them all that time for surveying. " measurement inside the unit, you are sure about the measurement—which is very important." The self-surveying capability of the DSUGPS geophone and the power of post-processing enable customers to use the instruments across terrain where seismic campaigns might not previously have been possible or cost-effective. The dual-antenna capability solved another problem as well. To correctly place sensors without GPS capability, testing crews may have had to inflict unwanted damage on local ecosystems. "When they were deploying seismic surveys, they would actually have to cut down trees and remove shrubs—basically destroy the environment in order to create lines, cut lines, to plant the geophones in," says Ryley. "So, one of the things that we came up with was 'OK we can save you a bit of that on the survey side if we can tell you the position on each geophone within a metre of accuracy,' which is easy enough to do. But the second part of that was: 'We can do that even in a moderate to dense forest.'" "The customer can put the geophones in the ground anywhere they want, and we'll be able to identify the accuracy of the geophones within 12 to 24 hours," adds Ryley. Because the geophones are not normally moved for several days, the time of data acquisition is not really a problem. There is a day or two to set the instruments up; next the surveys are conducted; then the crews move the geophones the following day—a far cry from the week to 10 days required by traditional geophysical survey techniques and instruments. "Within that period we'd be able to tell them the position of each geophone in the field down to a metre of accuracy," Ryley say. "So that prevented them from cutting down a lot of trees. It was environmentally much more acceptable for people who were doing oil and gas surveys, and it saved them all that time for surveying." Thinking inside the Box Achieving the heading accuracy given the small platform was a challenge, said Ryley. The baseline was just eight inches between the two patch antennas, Ryley says. "To try to 14 velocity 2013 get three degrees of accuracy on an eight-inch baseline is quite tough." That means a lot of processing takes place on the receiver card that goes into each DSUGPS and the NovAtel-provided postprocessing software that runs on the Sercel system software. "We provided the receiver and the antenna as two separate components. We worked together with the vendor on their industrial design and the interface into their geophone including the communication network," said Ryley. "We basically worked with them to get it built into an enclosure that fit on top of the geophone" In order to save time on signal acquisition, NovAtel supplies a base station to provide timing and control for the GPS portion of the geophone system. The base station receiver tracks the GNSS satellites and passes along the ephemerides or orbital locations of all the spacecraft in view of the ground so that the geophone/ GNSS units don't have to search constantly for the signals. However, although the base stations improve signal acquisition, they could potentially add delays into the system. "That is one of the things that we have to manage," says Ryley, "to keep the timing so tight. They have a very high-speed digital communications system between all of the geophones. We had limits on how much delay could go through the system, and it was critical that we minimized delay in the design." A lot of effort also went into keeping the costs down. "The cards had to be at a decent enough price to go into the customer's product," says Ryley, "because when you are selling 10,000 geophones, you can't really have $500 or $600 worth of receivers and antennas on each one of those. We had a very, very tight price point that we had to hit." But all's well that ends well. The system has now been tested successfully in France, in British Columbia in an area of dense forest, and across a giant, swampy area in central Mexico—a test that lasted more than six months. For more Solutions visit http:/ /www.novatel.com

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