Edited by Rachel Duncan 4th Edition ISBN 0-907649-91-2 London ...

60 RGS-IBG Polar Expeditions Manual
of compass and altimeter is a very powerful navigational aid but one that needs practice.
Reset it at every known height and be aware that indicated altitude is directly affected by
the changing atmospheric pressure. Using the altimeter as a barometer at a static camp can
assist in weather prediction.
6.4 Global Positioning Systems (GPS)
The variety and sophistication (and price) varies by the day! Most, as with other
computerised machines, have a selection of options far exceeding anything that is likely to
be required.
Features worth considering:
• Robustness;
• Reasonable water resistance (snow is wet!);
• Lightness;
• Ability to work at low temperature;
• Battery power and life required to run;
• Accuracy.
Batteries need to be long life (preferably lithium). The instruments (batteries) work
best when warm - therefore seek a model that easily fits your pocket or can be hung around
your neck and inside your clothing. LCD display can fail in extreme cold and you should
be aware of this and guard against it if possible.
The GPS is now almost considered standard navigation equipment, however, it is
not essential. Good map and compass work can be as efficient (and less likely to break
down) and certainly much cheaper. It will also make you much more observant of your
surroundings and save you quite a bit of money. In any case all GPS navigation should still
be backed up with normal map and compass use.
Many people also use GPS as a useful means of storing waypoints, as GPS: can follow
and even record points on the outward journey to enable you to race same route on return
journey, avoiding known crevasses, etc.
6.5 Sextants
Sextants have been so completely overtaken by new technology, particularly GPS, that
even mentioning them as anything other that as a historical footnote may seem odd.
However, historical re-enactment expeditions and retracing routes of polar pioneers is a
popular theme of current expeditions and therefore, this largely obsolete method is worth
mentioning briefly. Unless you are motivated by a particular desire not to use satellite
navigation systems ignore what follows and practise using a GPS.
Contrary to popular myth, the sextant is quite simple to use, particularly in the polar
summer where there are plenty of daylight hours. Two sun sights six hours apart could
position you to an accuracy of a mile or two. If you were to use a theodolite you could
bring the fix to within a few hundred yards. There are lightweight sextants available such
as the Zeiss Yachtmaster or even a plastic Ebco or Davies, although the plastics can be
affected by extremes of temperature. For serious polar journeys, metal sextants should be
used and these may have options of a built-in bubble in place of a mirror. A theodolite is
very expensive, heavy, requires a solid tripod and observations are time consuming.