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'Not another hobby', exclaims my wife - more clutter in the cupboards to go with the golf clubs, climbing gear, camera equipment, mountain bikes etc. So how can I justify this and why did I start such a strange pastime? What measurements do we actually take and where is this hobby going?
I belong to a group of ageing hill walkers who have been bagging Munros, Corbetts, and Grahams etc. for over 20 years, so obviously we have a keen interest in mountain summits. When the GPS revolution took place a few years ago, several of us bought these instruments. Although never replacing map and compass, we have used them quite extensively on the hills as an aid to navigation. One key property of these machines is their ability to provide ten-figure grid references. They are not accurate enough to pinpoint locations to within one metre, but we get reproducible results if we quote positions to the nearest five metres in each direction. However, these instruments are not good for accurate and reproducible height measurements, and so we do not use this function at all in surveying.
We soon found merit in recording ten-figure references of summit positions in a hills database. They are particularly useful when fed into a GPS instrument to locate difficult tops, e.g. a summit somewhere in a forest fire-break. Finding the exact position of any summit in bad weather is a doddle too. I can think of several hills I have had to repeat, having not found the actual summit in poor visibility.
So, we have the technology to go to a precise grid reference, but how can we be sure that is the summit of the hill? There are lots of hills out there where the summit position is not obvious. The solution I guess most of us adopt is to go to all the candidate positions so that we are sure the summit has been reached. Although I have always done this and will probably continue to do so, I felt there must be a better way to identify summit positions more accurately for the hills database, and this led me toward hill surveying.
At this point I knew nothing about surveying other than you had to buy a yellow jacket and always wear a hard hat even though there was nothing for 20 miles that could fall on your head. A quick read of a few Internet articles soon put me on the right track, but it was clear this could be a diverse and quite complicated subject - people do university degrees in it under the sexy name 'geomatics'. The key question I had to ask myself was 'what exactly do I want to do?', so I started with a list of criteria. I wanted an instrument I could put in my rucksack, was lightweight, accurate and inexpensive. I could not see myself going for a walk over the hills carrying 20kg of equipment costing £20000 (as some accurate GPS instruments do) on the off chance I would need it to locate a summit position. After all, one needs room in the sack for lunch. This led me to look at lightweight optical levels. Essentially these are telescopes with magnifications from X1 to about X5, with an attached spirit level. The technique is simple; look through the instrument from one point to another, once it has been set horizontally. Does the other point appear above or below the horizontal datum line? If it appears above, then your standing position is lower than the other point - high-point located, QED.
The simple optical level is great for a qualitative view of height differences, but is there anything that can give quantitative measurements too? Well the answer is yes, and the instrument is called an Abney level. (Not new technology; look in Wikipedia if you want to know more about Mr Abney, and look at the York Survey website if you are interested in buying one). Essentially this is a hand-held optical level but with the spirit level mounted on a steel protractor. The result is that you can measure an angle from one point to another. Knowing the distance between the two points, for example from the GPS grid reference or a tape measure, then by simple trigonometry the height difference of the two points can be calculated. So now we had a method of quantifying height differences as well.
Using Abney levels, Graham Jackson and I have been able to more accurately identify the summit positions of several hundred hills, and all this data has been fed into our hills database. This is all very well, but the instrument does have its limitations:
However, all this encouraged us to go further to a much more accurate instrument, so we purchased a kit of surveying staffs, tripod, automatic optical level plus other bits and bobs. Although not particularly heavy, this is still the sort of equipment that you would not take out on a country walk 'just in case'. So this is the kit we now take when we set out to go surveying. We have been focusing on a number of the double tops recorded in Alan Dawson's RHB updates. An automatic optical level is really a very sophisticated version of the hand-held level. The telescope has high magnification, and instruments range from X20 to X45, allowing objects to be seen easily at large distances. Also, the instruments have an automated compensating device, so that once they are set horizontally on the tripod, the automated system kicks in to make sure horizontal set-up is to within about 0.0002 degrees. So with this type of level, and using surveying techniques to eliminate systematic errors like earth curvature, refraction, instrument alignment etc., we are able to measure height differences of a few centimetres over several hundred metres of distance.
So what have we established with this more sophisticated gear? Some of our full surveying reports have been posted in the files section of the RHB newsgroup, so full details can be read there. However, to summarise, last year we:
Confirmed that Calf Top does not exceed 2000 feet.
So, where to from here? We have learned a lot about hill surveying techniques and have been able to improve them to gain greater accuracy in our quantitative measurements. We still have a list of double tops to look at, plus a number of other hills that will keep us busy. We are more than happy to investigate suggestions from any member of the RHB group, though our instruments do not enable us to measure differences between summits and cols over 150m lower. Also, any member of the group who wishes to join us on a surveying expedition would be more than welcome - some already have done so. Let me know through the RHB newsgroup or directly at firstname.lastname@example.org.
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