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

3D satellite photo showing some of the 775 ground survey points

PhotoSat publishes 21 new satellite surveying accuracy studies

3D satellite photo showing some of the 775 ground survey points

3D WorldView-2 satellite photo of Asmara, Eritrea, showing some of the 775 ground survey points that determine the 14cm PhotoSat surveying accuracy.

21 PhotoSat surveying accuracy studies from seven different stereo satellites

PhotoSat has published 21 new satellite surveying and mapping accuracy studies, now available on our website. The studies include data from seven different stereo satellite systems. The best results show elevation surveying accuracies of better than 15cm.

The accuracy studies include stereo satellite data from the following satellites:

  • WorldView-1
  • WorldView-2
  • WorldView-3
  • Pleiades-1B
  • KOMPSAT-3A
  • SPOT-7
  • ALOS PRISM

 

PhotoSat has measured accuracy on over 750 stereo satellite surveying projects

PhotoSat has delivered over 750 satellite surveying projects since 2007 and we have carried out accuracy evaluations on the majority of them. Most of the survey data on these projects belongs to our customers and cannot be shared publically; however, customers have provided feedback on many of these projects.

The results of these 21 new accuracy studies are consistent with our project accuracy evaluations and customer feedback.

 

PhotoSat accuracy test areas in Eritrea and California

The accuracy studies were conducted over two test areas. One test area is west of Asmara, Eritrea where PhotoSat has access to more than 45,000 ground survey points over a 50km by 20km block.

The second area is in SE California where PhotoSat uses a very accurate Opentopography.org open source LiDAR survey.

 

The effect of different numbers of ground survey points

The studies employed different numbers of ground survey control points for each test area and each satellite system. For some of the satellite stereo pairs the accuracy is significantly improved by increasing the number of ground survey control points.

For example, the WorldView-2 survey for Eritrea is accurate to 19cm in elevation with two ground control survey points, and accurate to 14cm in elevation with 21 ground control points.

In contrast, the accuracy of the WorldView-3 survey for the California test area is not improved by additional ground survey points. This WorldView-3 survey is accurate to 13cm in elevation with one ground survey control point and with 153 ground survey control points.

 

PhotoSat has been continuously producing satellite accuracy studies since 2007

In order to provide objective quantifiable accuracy data for stereo satellite surveying and mapping, PhotoSat has been continuously producing accuracy studies since 2007. We have previously published nine of these studies. The rest of the studies were used for calibrating and improving our processes.

 

21 new accuracy studies all processed with the same version of the PhotoSat processing system

The 21 new accuracy studies were produced with the most recent version (2016) of the PhotoSat processing system. Where possible we used satellite data produced by the 2015 or 2016 versions of the satellite operators’ ground processing systems.

 

Summary of PhotoSat 2016 accuracy study results

Satellite Test area km² GCP RMSE
WorldView-3 California 150 1 13cm
WorldView-3 California 146 153 13cm
WorldView-3 Eritrea 100 21 15cm
WorldView-2 California 173 1 15cm
WorldView-2 California 173 153 12cm
WorldView-2 Eritrea 100 21 14cm
WorldView-1 California 174 153 14cm
WorldView-3 Eritrea 198 2 19cm
WorldView-2 Eritrea 400 2 19cm
WorldView-1 Eritrea 100 21 19cm
WorldView-1 California 174 1 23cm
WorldView-1 Eritrea 420 9 23cm
Kompsat-3A California 144 14 21cm
Pleiades-1B Eritrea 189 74 26cm
Pleiades-1B Eritrea 189 1 28cm
Kompsat-3A California 144 1 50cm
Kompsat-3A Eritrea 130 11 48cm
Kompsat-3A Eritrea 130 1 53cm
SPOT 7 Eritrea 1,458 1 4m
ALOS PRISM Eritrea 2,300 3 2m
ALOS PRISM Eritrea 2,300 1 4m

See PhotoSat’s accuracy studies overview for full details.

For more information about PhotSat’s surveying accuracy, please see our satellite surveying case histories or visit the following links.

Satellite surveying

Mexico onshore oil and gas blocks

High Accuracy Surveying and Satellite Photos for Mexico Round 1 Onshore Blocks

As you probably already know, Mexico’s oil and gas blocks are up for auction and the next round includes the onshore fields. For bidding companies, detailed satellite elevation mapping and high resolution ortho photos can significantly help understand and assess the surface topography.

View the brochure for Mexico blocks satellite data (PDF).

Mexico onshore oil and gas blocks

Mexico onshore oil and gas blocks for bidding

 

PhotoSat can provide 30cm vertical accuracy, 1m bare earth elevation grids (DEM) for all blocks. These DEMs are produced from archive satellite images.

The benefits of having high accuracy surveying include:

  • Assessing environmental conditions including drainage and flood risk assessment.
  • Engineering grade accuracy allows for accurate assessments of the location of existing infrastructure (well sites, roads, pipelines etc).
  • Knowledge of the ground conditions reduces risk.

If the available satellite images used to produce the topographic data are too old for your purposes, we can acquire new satellite images on request. Contact us at info@photosat.ca for information on the data available over the block in question, and for pricing.

We can accommodate custom coordinate systems and are able to use many types of surveys for ground reference points. We can also produce the mapping without ground control points if nothing is available. More information on our 30cm accuracy satellite elevation mapping can be found on our main website.

If detailed base mapping is not required yet, we can also provide high resolution satellite ortho photos only over the desired block.

The following table outlines the existing 50cm resolution satellite images that are immediately available for all blocks. Included are the size of the block and the most recent ortho photo date. If you need more current information, we can task a satellite to collect new images.

Campos Burgos:
Block Size (sqkm) Archive ortho image date
Anahuac 30 October 2014
Duna 37 March 2014
Mareografo 30 March 2014
Calibrador 16 March 2014
San Bernardo 29 November 2013
Benavides 136 November 2013
Pena Blanca 26 June 2015
Carretas 90 November 2013
Ricos 24 August 2013
Campos Norte:
Block Size (sqkm) Archive ortho image date
La Laja 10 July 2014
Ponton 12 August 2015
Paso de Oro 23 October 2014
Tecolutla 7 January 2014
Barcodon 11 March 2015
Campos Sur:
Block Size (sqkm) Archive ortho image date
Moloacan 47 June 2015
Calicanto 11 May 2015
Cuichapa Pte 42 June 2015
Mayacaste 22 April 2015
Tajon 28 April 2015
Paraiso 17 April 2015
Fortuna Nacional 22 June 2015
Mundo Nuevo 28 May 2015
Topen 26 May 2015
Catedral 58 May 2015
Malva 22 May 2015
Secadero 10 May 2015

 

Our standard delivery is an ortho photo centered on each block covering 100 sq km. Pricing is based on the square kilometer, and custom sizes and shapes are available on request.

View the brochure for Mexico blocks satellite data (PDF).

Feel free to contact us for a quote, or for any questions: info@photosat.ca, 604-681-9770.