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.

 

 

Surface topography image and pipeline routes

Surface topography and pipeline route selection

Oil and gas pipeline routes are absolutely pivotal information. The route that a line has to take is always a trade-off between what you’d ideally like to have and what you have to accept: an ideal oil pipeline would run in a trench across a totally flat surface with constant temperature and no seismic activity. In real life, we have mountains, deserts, heat and cold fluctuations, seismic activity of all sorts, permafrost or rocky outcrops that necessitate raising the line on supports, and other obstacles. (And that’s without mentioning regulatory environment…)

On the one hand, knowing the terrain you have to get across lets you know what kind of pipeline you can have. On the other, knowing the pipeline plans lets you know what kind of geotechnical data you’re going to need to bring it home safely and efficiently.

When you’re researching pipeline route corridor alternatives, you’re equally faced with compromises. You need reliable, accurate surface topography data for the whole potential route corridor. Solid geotechnical data allows correct pipeline route selection and implementation, but getting it by traditional means is costly, time-consuming and environmentally damaging and can run the risk of damaging your local reputation.

Surface topography image and pipeline routes

PhotoSat elevation image and pipeline route options

 

PhotoSat’s highly accurate, engineering-quality digital surface topography allows you to examine and select multiple pipeline corridors and plan final routes, based on elevation data accurate to 30cm vertically. You can do it without risking survey teams in inaccessible locations or hostile environments. Usable engineering survey data is generated fast, typically within five days. We’ll typically supply our oil and gas clients with an engineering quality 1m topographic grid accurate to 30cm in elevation, 50cm or 1m contours, and a 50cm satellite ortho photo. And after it’s been used to select pipeline routes, the surface topography can be used for all phases of the project, because it’s accurate and comprehensive enough for most engineering tasks.

The accuracy of our surface topography has been proven in many accuracy studies using tens of thousands of ground survey points for comparison. View our proof of accuracy reports for more information. We have completed over 500 projects all over the world.

To learn more about our revolutionary satellite image processing system, or to find out how it could facilitate your oil and gas project, contact us at info@photosat.ca or 1-604-681-9770.