Ground control point

What mapping and surveying accuracy do I need for my mining exploration project?

By Gerry Mitchell, P.Geo, President PhotoSat

GPS survey of a PhotoSat survey ground control point.

Accurate topographic mapping and surveying of a mining exploration project requires a significant investment of time and resources.

 

For early stage mining exploration project work, 3m survey accuracy is sufficient.

Early stage mining exploration project work:

  • Geological mapping and outcrop sampling
  • Geochemical surveys
  • Geophysical surveys: magnetics, electromagnetics, induced polarization, gravity

Most early stage mining exploration projects require mapping quality topography, accurate to about 3m horizontally and 3m in elevation. This is similar to the accuracy of the hand held GPS units used by most exploration geologists to record geological observations and sample locations.

 

For exploration drilling up to the “discovery” drill hole, 3m survey accuracy is sufficient.

The initial exploration drilling will be focused on geological, geochemical or geophysical targets. Location of drill collars to 3m in XYZ is usually sufficient accuracy for the initial exploration drilling.  Once there is a discovery drill hole, project focus shifts to the confirmation and delineation of inferred resources.

 

When drilling to delineate resources after a discovery drill hole, you need better than 50cm survey accuracy.

Once the focus of the drilling campaign shifts to confirmation and delineation of inferred resources, survey quality topographic accuracy is required for the project. This is accuracy of better than 50cm in XYZ for drill hole collar locations and the locations of surface samples and trenches.

 

First, establish a survey benchmark with GPS.

The first and most important step in accurately surveying an exploration project is establishing a survey benchmark that is accurate to better than 10cm in easting, northing and elevation. The most reliable way of establishing an accurate survey benchmark is to record 12 hours of GPS signals with a dual frequency geodetic quality GPS receiver. PhotoSat provides guidelines for establishing survey benchmarks.

Mining project survey benchmark with the coordinates, horizontal projection, horizontal datum and vertical reference listed on the plaque.

 

GPS survey the drill hole collars, trenches and ground control targets.

The drill holes, trenches and at least three ground control targets should be surveyed with differential GPS.  For differential GPS surveys, the GPS signals at the benchmark, and the survey point must be recorded at the same time.  Many of the survey points can be surveyed while the benchmark survey is being recorded for 12 hours. The GPS signals at each of these survey locations should be recorded for at least 30 minutes plus one minute for each kilometer of distance between the survey benchmark and the survey location.

 

LiDAR, PhotoSat or Drone topographic survey of the project area

Depending on the size of the area, vegetation cover and location survey the project area to an accuracy of better than 50cm in elevation with airborne LiDAR PhotoSat or a Drone survey. The advantages of the different survey methods are discussed in a PhotoSat surveying white paper Comparison of PhotoSat, LiDAR, GPS and Drone surveying.

This survey will provide the topographic surface needed by the mining engineers preparing the reserve and resource volume calculations for your Preliminary Economic Assessment (PEA).

1m elevation contours and the locations of drill holes on the Almaden Ixtaca mining exploration project.

 

3D satellite image of the Almaden Minerals Ixtaca project showing drill hole locations and the discovery drill hole.

For more information, see the following:

Satellite Surveying
Mining Exploration
How accurate is PhotoSat surveying?
Accuracy Studies

How can modern satellites photos possibly be accurate to 20 centimeters in 10 kilometers?

By Gerry Mitchell, P.Geo, President PhotoSat

ground control survey points in eritrea test area

3D WorldView-1 satellite view showing the ground survey points in PhotoSat’s Eritrea test area.

 

My intuition rebels at the notion that a satellite orbiting 750 kilometers above the earth, traveling at 7 kilometers per second, could possibly take photos of the ground accurate to 20 centimeters in 10 kilometers. When you take into consideration that these satellites have scanning cameras which take their photos like push brooms, with the north end of the photo taken a few milliseconds before or after the south end, and that the whole satellite is vibrating while the photos are taken, it boggles the mind. It just does not seem that such high accuracy should be possible. However, the satellite photos themselves, checked with tens of thousands of ground survey points, clearly demonstrate that the accuracy is real.

How do the satellites and cameras work?

We engineers and geoscientists in the commercial realm don’t actually know how these satellites and cameras work. Almost all of the technical details of the imaging satellites, their cameras, and their ground processing stations is classified. Or if it’s not classified it’s certainly very difficult to discover. I’ve had many conversations with satellite engineers who seem like they’d love to tell me why their satellites perform so amazingly well. Sadly, they simply aren’t allowed to discuss classified technology with anyone without the proper security clearances.

Whenever I have one of these conversations, it always seems to me that part of what the engineer knows is public and part is classified, but the engineer cannot be sure that he or she can remember what is still classified and what isn’t so it’s safest to say nothing. I’ve had satellite engineers decline to confirm information that is published on their own company’s website. Needless to say, this can make for some very awkward conversations.

We engineers and geoscientists in the commercial world only have access to the satellite photos themselves, and very general public information about the satellites and their cameras.

How accurate are the satellite photos?

When the Digital Globe WorldView-1 (WV1) satellite photos first became commercially available in 2008, PhotoSat acquired stereo photos for a test area in Eritrea where we have over 45,000 precisely surveyed ground points. When we shifted the WV1 photos 3m horizontally to match any survey point, we were amazed to discover that all of the survey points within 10km matched the satellite photos to within 20cm. We eventually documented this discovery in an accuracy study white paper that is now published on our website.

Now, eight years after that initial WorldView-1 accuracy study of the Eritrea test area, we have processed hundreds of satellite photos from the WorldView, Pleiades, SPOT and KOMPSAT satellites and have come to expect this incredible accuracy. I’m still in awe that this is possible and I still don’t know how it is achieved. I do know that the photos are amazingly accurate.

black and white photo of over 15000 ground survey points in PhotoSat Test Area

WorldView-1 satellite photo over the PhotoSat test area in Eritrea. The over 15,000 ground survey points used to confirm that the satellite photo accuracy is better than 20cm in 10km are shown as black dots. The completely black areas are survey points every 20m along lines separated by 100m.

 

 Colour image of a one meter PhotoSat survey grid produced from the WorldView-1 satellite photos

Colour image of a 1m PhotoSat survey grid produced from the WorldView-1 satellite photos. The ground survey points demonstrate that the PhotoSat grid is accurate to 35cm in elevation.

 

 

satellite photo of a tailings beach.

Improving Safety for Mine Survey Teams: How Ground Surveying Fits Seamlessly With Satellite Topography

Mine survey teams perform a job that’s increasingly vital, increasingly technological – and more dangerous every day. When they’re doing preliminary work to acquire geophysical data for exploratory purposes, or scouting out pit placement, they’re subject to dangers including rockfalls and environmental dangers that can include severe weather and wild animals. Many mine sites are in inaccessible locations, in rugged terrain far from habitation, where it’s hard to put teams and even harder to get them out again fast when someone gets hurt.

At the same time, the industry is expanding into new regions where mining has previously been carried out with pick and shovel or even literally by hand. In sometimes socially-volatile places where old mine workings don’t show up on maps that are often themselves inaccurate, mine survey teams are saving the lives of miners by supplying engineers with accurate data – but they’re endangering their own safety to do it.

And what about when ground survey teams visit a working open mine to check for bench integrity? They’re sharing their working environment with heavy trucks and putting themselves in the way of slumping bench walls and falling debris.

PhotoSat’s 30cm accuracy satellite topography can provide a solution by filling in part of the puzzle. Mine survey teams will always be needed, but their exposure to risk should be minimized. When you get your elevation data from LiDAR or GPS, it can be significantly slower than PhotoSat’s unique geophysical processing technology. You’ll typically wait weeks, especially for aerial LiDAR. PhotoSat usually provides a client with engineering quality elevation mapping within 5 days, and there’s no boots on the ground so safety risks are minimized.

That doesn’t mean ground survey teams, LiDAR or other scanning technologies are redundant. Just look here to see how one of our clients, Suncor, combines multiple scanning technologies to get the data they need.  In 2014, Suncor and PhotoSat presented on the benefits of incorporating satellite surveying into their survey process for their Tailings Reduction Operation (TRO). With many areas of the TRO cells inaccessible to ground surveyors, the satellite-based technology reduced exposure to hazards.

But it does mean there’s a way to get a fast, engineering quality mine survey that can be used for multiple engineering and planning applications – without putting anyone in harm’s way.

To find out more about PhotoSat’s 30cm accuracy satellite topography for mine surveys, contact us at info@photosat.ca or 604-681-9770.

satellite photo of a tailings beach.

High resolution satellite photo of a tailings beach.

elevation image of a tailings beach

PhotoSat elevation image of a tailings beach