Smart surveying in the Outback

When someone imagines the Australian outback, they’re picturing Australia’s largest state, Western Australia (WA), which occupies an entire third of the continent.

Nearly all WA residents live in Perth, with the rest of WA reminiscent of the United States’ historic Wild West — sparsely populated towns with little infrastructure. That wild beauty and remoteness can also make surveying a less-than-beautiful experience.

“The outback of WA is a real test on my adaptability and logistics skills,” said Phil Richards, a professional surveyor and associate director with 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.”

Technological challenges that add to the complexity: limited mobile phone service, time-consuming RTK base station setups, inconsistent RTK cellular or radio communication, and geodetic control points that are difficult to access.

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

Camp breakfast: The R10 receiver rests on a spur while Phil Richards dines out. (Photo: Trimble)

The case for a new approach

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

Managing 10 prospect sites across 300 km, the number of drill holes can vary from year to year, but there can be as many as 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 the distance to each, Richards would set up between two and nine RTK base stations on known control points to set project control. Using his Trimble 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 had added hours onto 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 numerous 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,” said 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 or move it. The reduced number of collars and the increased distances between them required a more efficient method to make the project profitable.”

Taking the R10 off the vehicle mount. (Photo: Trimble)

Richards decided to test Trimble’s CenterPoint RTX correction service as an alternative. 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 at 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-centimeter horizontal accuracy in WA, Richards said the technology regularly delivered on performance. Most importantly, this technique enabled him to work without a base station and obtain real-time GNSS positions with centimeter accuracy even in isolated WA.

Integrating Trimble’s CenterPoint RTX into his workflows enabled Richard to use a single GNSS receiver system, much like working within the VRS networks available in the more populated areas of Australia.

Into the Outback

For the 2019 campaign, Richards and a colleague were contracted to acquire accurate 3D positions for 13 drill-collar holes stretched across two major prospects about 150 km apart. Their area of interest was 700 km northeast of Perth.

Within a 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 the positions of each collar hole. Despite the rough terrain, they finished both prospect sites in 1.5 days, compared to 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,” Richards said. “It’s far quicker than setting up base stations — I saved 50% of the time using RTX on this campaign. I’m 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.”

Featured photo: Trimble