When you hear that your GPS is
accurate to 15 meters, just what does that mean to you in the backcountry?
This is a frequent topic in my GPS
land navigation class.
Today, a GPS receiver is accurate to
the design specifications of the model. Generally, a GPS is accurate to plus or
minus 15 meters (a circle with a15 meter radius or 30 meters in diameter.) Many
models offer more accuracy through the technology of the Wide Area Augmentation
System (WAAS); 3 meters is possible. (Note that to take advantage of WAAS that
option must be "enabled" in the setup function of the main menu.)
There are several factors that
contribute to the accuracy of the signal data received and geographic
coordinates displayed. Some of these factors include:
- Number of satellites signals being received
- Multi-path interference (signals reflected
off a surface yet being received)
- The age of the unit and antenna model/type
- Receiver sensitivity
- Atmospherics (such as solar flares and sun
spot activity)
To counter the factors
listed above the wilderness traveler has only a few options and these include:
- Buying a new unit
- Relocate to an area with a clear sky view
(get away from trees)
- Give the receiver more time to capture and
process the satellite signal
Giving a receiver the
time to capture and process data received is especially true with the older
models. For example, I have students attending my classes bringing in the older
Garmin 12, Garmin Etrek Summit, Magellan 315 and Magellan Sport Track. These
are old but functional, usable and models that will definitely get one back to
the truck or trail head. My recommendation is to give the receiver the time to
do the job; this could be five minutes. (If it takes longer than 5 minutes you
may have a problem with the receiver.) Remember, with the older models, if your
travel over 50 miles from the location where the unit was last used, it will
take more than 5 minutes to "re-initialize;" check the owner's
manual.
No matter what the age of the GPS
receiver is, my recommendation is to consider that the traveler is moving down
a lane in the backcountry. See below:
In the example above, the hiker will
be somewhere in the lane traveling from "start" to "elk
camp." At one moment in time the hiker may very well be in the center of
the lane but a short time later his actual position will shift ahead, to the
side and so on.
I understand that this may not be as
"spot on" as some would like but overall the GPS will provide adequate
information to reach the destination.
Depending
on the model, I've found GPS compass information to be variable. Rather than
use the GPS compass/electronic compass information exclusively I'll use my
magnetic compass too.
Don't rush navigation. Navigation
deserves the time, patience and attention to detail as does any other skill of
the backcountry.