Many of us have an altimeter as an integral part of our mountain watches, but how many of us know the skills of navigating with an altimeter?

Here are 5 tips on how to use an altimeter as a navigation tool.

Before we begin however, a note of caution, altimeter watches rely on barometric pressure to calculate altitude and as the barometric pressure fluctuates so does the altitude reading, and this can lead to serious errors if not addressed.

It is important to re-calibrate the altimeter regularly by re-setting it to the correct reading when a known altitude is reached, such as a summit, col or spot height. Read the height from the map, and adjust the altimeter accordingly. This is particularly important in areas where the pressure may change rapidly as weather systems track across the globe, for example over Ireland and the British Isles. Here adjustments should be made every couple of hours, as and when the opportunity presents itself.

 

  • Knowing how high you are (absolute altitude)

Knowing how high you are (your altitude) and how far you still have to climb is a great way of monitoring your progress. This is particularly helpful on a long uniform slope with little in the way of landmarks, or when visibility is reduced as clouds descend or when night falls.

In poor visibility, reading off the altitude can indicate if you are at the summit of your mountain, or merely a lower, subsidiary top.

 

  • Ascent rate

Checking your ascent rate is a great way of monitoring your progress. By checking both your increasing altitude and the time taken you can estimate your arrival time at the summit.

For example, if you have a 1,000 metre climb to undertake, and you have completed the first 200 metres of ascent in 30 minutes, then it should take you another 2 hours (4 x 30 mins) to reach the summit. You can check your progress against the estimated arrival time, and if all is going well, reach the summit. Equally, you can re-assess your plans or turn back if you are falling well behind the clock.

 

  • Descending a slope

Navigating with an altimeter (1) If you are descending a slope, perhaps in poor visibility, and you are required to make a change of direction to avoid steep and craggy ground, check the map for the height at which you need to turn off and when your altimeter reads that height, you can make the necessary change. (In the example below this is at the 790m contour).

This technique would work equally well if you were ascending a slope and needed to change direction.

 

 

 

  • Traversing (Contouring)

Maintaining the same height as you traverse around a slope, (following a contour line), can be notoriously difficult in bad weather. There is a strong tendency to lose height as you go, and drop down the slope.

Checking that the altitude reading on your watch remains constant allows you to maintain your height and traverse the slope without any problems.

 

  • Relocation (Aspect of Slope)

Navigating with an altimeterIn a previous blog on relocation techniques, I explained how to use your compass to determine the aspect (direction) of slope and thereby determine what side of the hill you were on:

Feb 2017 Relocation Techniques in Navigation)

This navigational technique can be combined with an altimeter reading to determine your exact location on that slope. In the example below the altimeter reads 600 metres, which places you at the red cross on the map.

 

 

Used in combination with other navigation skills, and your map and compass, an altimeter can be a valuable addition to your navigation toolbox.

One of the most important navigation skills is being able to relocate yourself when you have become ‘lost’ or more correctly, ‘temporarily misplaced’. Having the relocation techniques to deal with such a situation is a key element in being a competent navigator.

Firstly, do not panic. Stay calm and stay where you are.

Many people, on realising they are misplaced, will press on more quickly, or walk in any direction in the hope of finding something they recognise, thus making the problem worse.

Have something to eat and drink, this will both give you time to calm down and increase your blood sugar to help you think.

Gather All Available information

What can you see around you? Are any features in view, such as a forest edge or a stream, and what is the shape of the terrain around you, which way is the ground sloping?

How far have you walked since your last known position, (the location where you were last certain of your position). How long did it take you? What distinctive features did you pass, such as a path junction, knoll or forest edge?

See if you can locate any of these features on your map, and use the information to narrow down the possibilities.

Aspect of Slope

If the terrain you are on is sloping it is possible to use this important technique to help you find your position. Use your compass to take a bearing directly down the line of the slope, that is the line that a rolling ball might take, adjust for magnetic variation, and then search the map for slopes with that aspect.

Mountain Navigation - Aspect of slope

In the example above, if we know we are somewhere in the vicinity of hill 668, and we take a bearing down the slope of 198°, then we can eliminate all slopes that do not have that aspect.

With our bearing set on the compass, we can line up the orienting lines in the compass housing with the north-south grid lines on the map. By moving the compass around the map we can locate the slope(s) where the long edge of the baseplate is pointing directly down slope, (and is at right angles to the contours).

We can now locate ourselves somewhere on the southwest slope of hill 668.

Back Bearings

If you have been walking on a bearing, and the indications are that it was incorrect, then it is still possible to return to your last known position.

Instead of walking with the red end of the compass needle aligned with the orienting arrow, (keeping red in the shed), turn yourself through 180° and align the white end of the compass needle with the orienting arrow, (put white in the shed).

Following this bearing and remembering the paces, or time it took, you can return you to your previously known position. This will only work if you did not stray wildly off the original bearing, or wander around the hill hoping to see something you recognised.

Resection

Resection can be a time consuming process. It also relies on the fact that you can see far enough to identify two, and preferably three, major features that are also on the map such as hill tops or stream junctions.

It could be argued that if you can identify these features then you are not misplaced! However, under certain circumstances it can be a useful technique. If you are somewhere along a long, featureless ridge for example, and need to pinpoint your position more accurately.

Mountain Navigation - Relocation

 

  1. Take a compass bearing to a feature, and after converting it to a grid bearing, place one of the top corners of the compass baseplate on the feature identified on the map.
  2. Carefully manoeuvre the compass until the orienting lines in the housing line-up with the north-south grid lines on the map, being sure to keep the corner of the baseplate on the feature and the orienting arrow pointing north.
  3. Your position now lies somewhere along the long edge of the compass base plate, you can now plot this line on the map using a pen, (see red lines above).
  4. Repeat this for one or more features to pinpoint your position, depending on the accuracy with which you took the bearings your position will lie at the intersection of these lines.

 

Article by Russ Mills – Mountaintrails

These, and other navigation techniques, can be found in ‘Navigation in the Mountains’, published by Mountain Training and available through our website shop here:

http://mountaintrails.ie/shop/navigation-in-the-mountains-book/