Tips and Techniques For GPS Usage In The Desert


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A GPS needs a CLEAR VIEW OF THE SKY to "see" the satellites. It is a line of sight device. Of course you cannot see the satellites but the GPS can see the signals being sent. It may work on an iffy basis in the deep woods, it will not work at all in a deep canyon and of course it does not work in caves, buildings or tunnels. It DOES WORK very well in the desert where a clear view of the sky is almost always available. Weather for the most part is not a factor.

The interesting thing about GPS, as I may have mentioned before, is that they are so accurate, that in some cases when comparing your position to a map, you may think you are NOT on the designated trail. Keep this point in mind. The original GPS signal with SA (a form of fooling or spoofing the signal) turned on was 100 meters. In rough figures that is the length of a football field. With SA turned off as it is these days your accuracy is 35 meters, or around 100 feet. Newer units incorporate WAAS and if your GPS is receiving the WAAS signal then accuracy is around 3 meters or 10 feet. Think about that again, 10 feet! Just 3 long steps and you are in a known circle! Just a little bigger area than the Round King sized bed at that fancy Las Vegas Hotel.

Now look again at the Topo map in your hand. Somewhere it may say NAD27. What that means is the original map was based upon surveying instruments and procedures from the 1920's. Many of the more remote Topo maps are still from that era. Yes, it may have been "updated" in 1984 but just be aware of how the map was made. In other words, be knowledgeable and smart when using today's technology with your Great Grandfathers map When I first started with GPS I kept getting "lost" only to realize I was trying to be too perfect when the map wasn't. Think again of the maps that Christopher Columbus made and even the US maps from 1850's and you get the general idea. Your GPS is FAR more accurate than the trail drawn on an older Topo map.

One other point passed on to me by my friends at the USGS. The altitudes shown on some Topo maps are notorious for being a "WAG". Today's GPS units, when combined with a Thommen hand help altimeter, are decades ahead of the printed altitudes on some of these Topo maps. Once again don't assume you are lost and at the wrong altitude because your GPS shows you at 5400 feet but the Topo map may says 5600 ft. Your GPS and Thommen altimeter, assuming it was set correctly for the prevailing barometric pressure, will probably be correct.

While we are talking about maps, the newer ones from a publisher such as Tom Harrison for example, are pretty good. In fact I would almost say they are better than pretty good but someone will accuse me of peddling Tom's stuff, so I won't. Not true, but if you want to try your navigation skills with your new High Tech Toy then you will enjoy maps produced by publishers such as Harrison and others. They will build your skills and make you a better navigator. When you do buy maps be sure to get the newer versions with GPS compatibility. Older Topo maps will not have that feature but all maps usually have Longitude and Latitude of some type printed on them.

It can get bewildering on knowing which form of navigation to use. In a nutshell UTM is better for hiking than Long and Lat. Yes, I can hear the chorus swelling behind me saying, "that is not true", but I will let you be the judge later. Lat Long is great is you truly understand the world is divided into 360 degrees, London is at zero and San Francisco at 118 or so. So do we really hike from London to San Francisco? No, and in that vein UTM has Lat Long beat. If you are flying from SFO to LHR then Lat Long wins hands down but are you a pilot?

UTM works well because most of us can visualize the length of a football field at 100 meters or so. If we are going to hike 3000 meters then simple math tells us that is 30 football fields. The GPS can count up or down this 3000 meters. If you use Lat Long the GPS may tell you you have zero degrees, 1 min and 37 seconds to go in degrees, not time. What does that all mean? Why bother, just stick with UTM and make life easy. However things get to be fun when your map is printed in Lat Long and you want to use UTM. Tom Harrison, (remember what I said about his maps?) where are you? Don't get turned off by all this mumbo jumbo techno talk, it really is easy. I just brought it up to let you know that two major systems exist.

(This story will continue as time allows)