How do you measure a mountain?
In the past week of so, you may have read about plans by Nepal to re-measure the height of Everest. Apparently being the world’s highest peak at 8,848m just isn’t enough – they want to use the latest satellite technology to get the most accurate measurement possible.
Everest
It’ll also an opportunity to settle a long standing disagreement between China and Nepal. According to the BBC, the Chinese argue Everest should be measured to its rock height, while Nepal maintains that any figure should include the snow on the summit – which would add about four metres.
This in itself is an interesting debate – what do you think is fairer?
Anyway, it’ll be two years before we hear the results, so in the meantime I thought it would be worth explaining how you actually go about measuring something as huge as a mountain.
Obviously Britain doesn’t have any peaks of Himalayan proportions, or any with 4 metres of standing snow, but whether it’s Everest or Ben Nevis, it’s not necessarily an easy task.
The most accurate method, which the Nepalese are using, involves using GPS satellite technology, or more precisely GNSS (Global Navigation Satellite Systems) technology, of which the American Global Positioning System is just one example.
Satellite technology will give you an instant position to a few metres, but the height will not be very accurate, so the GPS unit has to remain stationary and record data for a period of time – preferably several hours. Easier said than done in some conditions!
Photogrammetry
That data is then “post processed” where it is combined with data from other stationary receivers (what we call OS Net in Britain) to obtain a more accurate height measurement. The more data collected the more accurate the resulting height.
Using this method, accuracy of just a few centimetres can be achieved and I’m sure this is what the Nepalese government are hoping for.
So that’s the answer right? Well not quite. Satellite technology has transformed map making, however because of the time it takes to get an accurate height, it remains impractical to measure every mountain in this way. That’s why we use an alternative method for measuring most of Britain’s hills and peaks.
It called photogrammetry, something we’ve covered before on the blog. It involves flying the area to be measured taking overlapping, high resolution photos from which a 3D representation is then created. Measurements can then be taken that translate directly to positions and heights in the real world.
This allows large areas to be surveyed quickly and safely and to an accuracy of 3-4 metres – more than enough for most uses in what are usually remote areas.
Having said that, when a mountain is just above or below a special threshold, that margin for error is just too tantalising for some…
I hope that’s interesting, any questions just let me know.
[Everest image by claude_florin via Flickr]
GI explained, Using GI and maps
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Everest, global positioning system, GPS, how do you measure a mountain, how to measure a mountain, Mount, Ordnance Survey
Themocracy
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Hi, this is an interesting topic, thank you for sharing it. However it’s all very well knowing what height the summit is in regards to sea level or whatever datum the Nepalese use but how do you determine the actuall height of a mountain, what definition gives to base height?
Regards
Kevin Perrina
Hi Kevin, I’m glad you enjoyed the post.
It’s a good question, and honestly I’m not sure what they will be using for Everest, but the ‘standard’ way, and certainly the way on nearly all maps, is to measure the height of the summit above ‘Mean Sea Level’.
At Ordnance Survey this is the method we use, where Mean Sea Level has been determined by measuring the tide over many years.
There is a bit more information on that here – http://blog.ordnancesurvey.co.uk/2010/07/surveying-our-antiques/
Paul
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