How can you navigate / determine your location in thick fog?

In the UK the prevailing wind blows from the south west and trees/ bushes grow away from the wind so assuming one can see a tree it should be easy to determine the other points of the compass. Elsewhere in the world it would be sensible to determine the direction of the prevailing wind prior to setting out.

posted about 9 years ago

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Marcle UK‭

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according to the boyscout handbook you can use moss (apparently it usualy/always grows on the North side of the tree...)

It is generally believed that in northern latitudes, the north side of trees and rocks will generally have more luxuriant moss growth on average than other sides. This is assumed to be because the sun on the south side creates a dry environment. South of the equator the reverse would be true. However, naturalists feel that mosses grow on the damper side of trees and rocks.[3] In some cases, such as sunny climates in temperate northern latitudes, this will be the shaded north side of the tree or rock. On steep slopes it may be the uphill side. For mosses that grow on tree branches, this is generally the upper side of the branch on horizontally growing sections or near the crotch. In cool damp cloudy climates, all sides of tree trunks and rocks may be equally damp enough for mosses. And different species of mosses have different moisture and sun requirements so will grow on different sections of the same tree or rock.

Wikipedia page on Moss

posted almost 13 years ago

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mjrider‭

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There's a whole bunch of standard map and compass techniques you can use without a GPS.

If you know your location before the fog came down, then you're not lost - you just can't see so far. Change your navigation strategy to have shorter legs, and pick tick points that will be within your vision. Pay particular attention to changes in trail direction and contour interpretation. If you have a good handrail feature (path/river/fence) use that too.

If you are 'lost' and need to re-locate yourself, start by looking around you. Are you by a path or stream, and if so, what direction is it going. What's the terrain doing around you. In particular, in the mountains, what is the slope aspect? (i.e. what's the compass bearing of the 'fall line'). If you have a (correctly set!) altimeter watch that can help reduce the possibilities too.

If you're lucky this will be enough to give you a definitive fix (or enough clues to tell you which way to go, even if you're not 100% sure of position.

But often, there aren't enough definitive clues within sight to fix your position. If so, it's time to move! Not far - maybe 100m or so. Choose the direction to move in based on your previous guesses (ie, pick directions where the presence/absence of particular expected features en route will narrow the possibilities) and obviously avoid directions that could take you near steep drops. Add the clues from your new position to those of the old one. Repeat, if necessary.

There's a whole bunch of books on navigation. My favourite is this one: Ultimate Navigation Manual.

posted over 12 years ago

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Roddy‭

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This depends of course on the tools you have and what your overall situation is.

For example, if you know that you are on a certain path and you have a compass, and if you are on a slope, you can try to figure out the direction of the slope and compare that to the slopes along the path you are on using your topographic map.

posted almost 13 years ago

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Lagerbaer‭

51 reputation 3 10 5 0

With fog, the only thing you're losing is extended visibility. This shouldn't throw off your plan too much, unless you were navigating by watching far away landmarks.

If you were on a trail, stay on it. There's no need to wander around. If you can't see anything and traveling is becoming dangerous or you're not sure where you're going, then stop and wait for the fog to lift.

If it's getting dark, you might have to setup camp. Hope you have an emergency kit!

Ultimately it's a judgement call. If you think you can keep marching on without getting lost, then don't worry about the fog. But if the fog is too thick, stop and wait it out. Remember, patience is a virtue :)

posted almost 13 years ago

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Hartley Brody‭

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In poor visibility you need to fall back on the basic navigational techniques of dead reckoning and any terrain features that you can still positively identify and follow.

Dead reckoning involved keeping close track of the direction you are walking in and how far you walk. With practice this can be reasonably accurate, especially if you can augment is with hints from the terrain eg whether you are going uphill or downhill. However the problem is that even with great care it is easy for errors to accumulate and difficult terrain can make distance estimation very difficult.

You can compensate for this to some extent be being conservative in your navigation eg by taking a route which is easy to follow rather than the quickest or most direct. For example by following a ridge, stream or treeline.

Similarly if you are aiming at a point on a linear feature for example a bridge over a river it is safer to 'aim off'. For example if you know there is a bridge due north of you crossing a river which runs east-west, then rather than taking a bearing due north aim off to the east by a good margin so that you know for sure that when you strike the river you need to head west to find the bridge.

Another key point is that if it looks like the weather might be closing in, that is the point to stop and make absolutely sure that you know where you are and double and triple check it. At this point make a decision about whether to continue on your planned route, stop, turn back, find an alternate route or head for an achievable place to wait out the bad weather.

If you know your exact location when visibility gets bad (which you should) then think carefully about the worst case scenario of getting badly lost falling off a cliff or stumbling into a bog is going to be worse than an unplanned night on a hill.

posted over 8 years ago

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Chris Johns‭

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If you know about the wind then that might help you. For example, a northerly wind blows from the north to the south, likewise an easterly wind is a wind that originates in the east and blows west and so on.

posted almost 13 years ago

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tushar‭

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Pacing and timing can be used to aid navigation in poor visibility. Both methods improve as you gain experience by practicing pacing and timing over different terrains.

• Pacing by counting steps (beads on your compass lanyard or a mechanical counter will help you avoid loosing count) to estimate distance travelled from a known location.
• Timing based on, for example, Naismith's Rule to estimate distance from a known location.

You could also use a rope of known length to measure distance.

A great example is safely navigating off the summit of Ben Nevis which requires following a bearing of 231 degrees for 150 metres, then following a bearing of 282 degrees.

posted almost 13 years ago

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Graham‭

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If you need to walk on a compass bearing in poor visibility, stand still, and send someone out in front of you on the correct bearing for a distance (probably as far as you can see). Have them stand still, then walk to them. Repeat. It's slow going, but you will be walking on the correct bearing, and more accurate than just holding the compass out in front of you.

Location finding is a bit trickier - I guess not being lost in the first place is the best idea! Look for any features that may be visible that would be on the map, or any identifiable features that you come across while walking. If you think you know roughly where you are, walk to a feature, like a stream, and if you don't find it then you need to reassess.

posted almost 13 years ago

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Chris‭

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