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How correction services enhance remote surveying

Western Australia (WA) is the resource center of Australia. It contributes some 58 percent of Australia’s Mineral and Energy Exports, according to the Department of Mines and Petroleum. With 92 percent of its 2.6 million inhabitants living in the southwest corner, the rest of WA is a variation of the “Wild West”––sparsely populated towns with poor infrastructure, rugged terrain and a landscape of reds, greens, coppers and browns that stretch into the horizon. In other words, when someone pictures the Australian outback, they’re picturing WA. That same rustic beauty and isolation can make surveying a challenge.

“The outback of WA is a real test on my adaptability and logistics skills,” says Phil Richards, a professional surveyor and associate director of Perth-based RM Surveys. “It can take 1.5 days to get to your first site and once there, you’re totally isolated, with no resources and climate conditions that can range from 0 to 50 degrees Celsius. The sparse, rugged road systems make navigating anywhere a long journey. And if the weather turns bad on your job and you didn’t plan well, you could be completely stranded.”

On top of the inherent unpredictability of the outback, there are technological challenges that increase its complexity: limited cell phone coverage, inconsistent RTK cellular or radio communication, and geodetic control points that are hard access.  

Advances in precise point positioning (PPP) technology, however, have helped to resolve these obstacles and enable surveyors to optimize their real-time productivity without compromising accuracy. For Richards, who specializes in remote surveying work, this next generation GNSS enhancement has helped tame the wilds of WA, enabling him to increase data collection efficiencies, reduce costs and boost the company’s bottom line.

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The case for active mining

With his aptitude for remote surveying, Richards has focused much of his work in WA on supporting active mining companies. For example, for the past 15 years, one iron ore producer has contracted him to travel more than 600 km from Perth to measure exploratory drill hole collars. Drill collars, the remnants of drilling activity, are 3-mm-thick segments of PVC, about 150 mm in diameter, which protrude about 300 mm out of the ground at typically a 60-degree angle. Measuring the center of that above-surface collar is critical in the exploration process to enable the company to develop a geological model of its mineral resource underground.

Managing ten prospect sites across 300 km, the number of drill holes could vary from year to year, but often they would have up to 100 holes spread out over a few prospects at a time. Since 2007, Richards has been using Trimble® R8 and, more recently, Trimble R10 GNSS receivers and RTK technology to acquire the drill collar measurements.

On average, each prospect is 5 km by 2 km and has its own coordinate network. Depending on the number of collars and distance to each, Richards would set up an array of RTK base stations (between two and nine) on known control points to set project control. Using his GNSS receiver, he’d either drive or walk to each drill collar, set the foot of the range pole on the center of the collar at ground level, take a reading and record the measurement in Trimble Access™ field software on a Trimble TSC3 controller. Although the need for multiple base stations added hours to the projects, the RTK method consistently provided the needed accuracy.

X hits the spot

In 2015, the iron ore company restructured its mineral exploration program.  Rather than drill large numbers of exploratory holes across a few prospects, the new focus was to drill fewer holes spread over the entire project area. That was going to be problematic for Richards’ traditional RTK routine.

“Previously, when it was predominantly surveying and less traveling, the RTK approach worked well for the project, even though setting up base stations is time consuming,” says Richards. “But when that switched to less surveying and more traveling, continuing with RTK was going to increase costs because each time I have to set up my base station, that’s an extra hour. If I have 10 drill-collar zones, that’s 10 hours. And if my base station is 10 minutes away, it adds more time and expense if I have a problem with it or I can’t get a reliable signal, and I have to travel back to it to fix it. The reduced number of collars and the increased distances between them required a more efficient method to make the project profitable.”

Richards’ dream solution would enable him to use a single GNSS receiver system, much like working within the VRS networks available in the more populated areas of Australia. The approach would give him mobility and flexibility and consistent real-time GNSS measurements.

He began testing other modern solutions, including Trimble’s CenterPoint® RTX correction service. CenterPoint RTX is built on a network of GNSS tracking stations around the world that stream multi-frequency, multi-constellation data to the company’s network control centers. Advanced data processing algorithms analyze the three main error sources: satellite orbits, clock offsets and atmospheric effects and develop models and correction data. This information is delivered to GNSS rovers via L-band satellite communications. The rover combines the correction data with its own satellite observations to produce accurate positions.

Richards ran five trials in conjunction with varied exploration surveys to test the reliability, efficiency and accuracy of the RTX approach as a viable alternative to RTK. Choosing different test sites across 1,000 km of terrain, he took RTX measurements of survey control points with his R10 and compared them to the same positions acquired with RTK. Although the CenterPoint RTX can take up to 15 minutes to reach sub-2 cm horizontal accuracy in WA, Richards says the technology consistently delivered on performance. Most importantly, this technique would enable him to work without a base station and obtain real-time GNSS positions with centimeter accuracy anywhere––even in isolated WA.

Based on the trial results, he adopted the CenterPoint RTX technology to integrate into his survey workflows.

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Into the outback

The R10 and CenterPoint RTX technology have been Richards’ core technology for each campaign since the drilling project.

“With CenterPoint RTX, I can get right to work as soon as I reach my first drill collar site,” says Richards. “I don’t need to spend time with a base station so I’m much more mobile and that alone can save me a whole day’s work. I’m not limited by distance or the base station’s signal.  It’s a brilliant tool and it’s a game changer for remote surveying.”

A couple of years ago Richards was contracted to survey 40 drill collar holes spread around all ten of the client’s prospects. Richards and his colleague mounted the R10 GNSS receiver on their vehicle and set out for the first site at sunrise one morning. About 30 minutes from arriving on site, they activated the CenterPoint RTX and monitored the initialization via Bluetooth from inside the cab. With the RTX solution initialized and ready to go, Richards carefully dismounted the R10 and set the range pole onto a control point he previously established to calibrate site control. He navigated to the first stake indicating a collar, verified the collar number given, set the R10 on the center of the collar and via the TSC3’s software he entered the collar number and recorded the RTX 3D position. He then moved on to the next stake and followed the same routine, repeating it 39 times over 2.5 days.

“With the distances involved and the large area we’re working in, the RTX really comes into its own for this project,” Richards says. “If I had had to use an RTK approach, and set up multiple base stations 10 different times, it would’ve added at least another day to the job. If you take all the driving out of it, we reduced 10 hours work of actual surveying time to one hour. That savings not only pays for my yearly CenterPoint RTX subscription, it’s a smart way to increase your profit line.”

They processed the data back in their office in Perth. The measurements were verified and input into a spreadsheet for the client.

For last year’s campaign, Richards and a colleague were contracted to acquire accurate 3D positions for 13 drill collar holes stretched across two major prospects that are about 150 km apart. Their area of interest (AOI) was about 700 km northeast of Perth.

Using the small WA town of Cue as a base, they drove to the first prospect about 60 km away, using the travel time to initialize the CenterPoint RTX positioning solution. Within the 15-km-wide area, they had to acquire measurements for eight drill collar holes. They calibrated the R10 receiver to the nearest control point to tie into the site’s coordinate system and moved through the area, methodically recording positions of each collar hole. Despite the relatively few collars to measure, it took Richards and his colleague about five hours to collect the data because the rough terrain made the site difficult to navigate.

Still daylight, they drove to the next prospect, which contained five holes at significant distances apart. By the time they reached the site, they could only complete one hole, so they camped out on site and measured the remaining four holes the next day. All told, they finished both prospect sites in 1.5 days––a project that would have taken 2.5 days had they used RTK.

“Given the project format, with so much travel time and less surveying time, RTX is really the only way to do it,” says Richards. “It’s far quicker than setting up base stations––I saved 50 percent of the time using RTX on this campaign. I am more efficient; I’m able to keep costs down; and I have the confidence in the system that I know I’ll deliver on accuracy. It’s hard to justify using any other method.”

There is little Richards can do to reduce travel times in the remote areas of WA but venturing into the wild with a reliable and cost-efficient tool that can produce real-time, centimeter-accuracy positions in seconds is a reassuring advantage for staying competitive.

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