|
|
|
Hunting Technology – GPS So
what is “GPS”? GPS stands for Global Positioning System. It is a free, government-provided system for determining precise positioning anywhere on Earth. On the government end is the “constellation” of 24 satellites (plus three spares) which orbit the earth in various locations. On the user end is a handheld receiver, which does the mathematics of triangulation, and displays location and navigation information. What
do I need?
In the simplest of terms, a receiver with batteries. GPS was rolled out
in the early ‘90s, and earlier receivers were slow and expensive. Today, most
receivers have matured as far as their technical computation functions are
concerned. Now you can get a good, basic receiver for around $150.00. As the
name implies, a receiver is only a one-way device. It is only designed to
receive signals from the satellites. So how does it work? Well, it’s
complicated, and yes, it’s rocket science. Basically, each satellite knows
it’s own position and the position of the other satellites. Each satellite
sends a sting of data with information regarding its internal clock, position,
and the positions of nearby satellites. What the receiver does, is take the data
from the satellites (it needs three for position, four for altitude), and
computes a triangulated position based on the calculated positions of the
satellites. Believe it or not, it works very well! And it is now very accurate! What
can I use it for?
The best way to use a GPS is for location marking. What this means, is
that when you set up camp, or park your truck, you turn on your receiver, allow
it to position itself, and then save the position as a “waypoint”. Then shut
it off to conserve the battery. Later, when you are out, you simply power up the
GPS, let it compute its position, then select the navigation function for it to
direct you to the waypoint (as an example, your truck). Obviously, it’s VERY
important that you never rely solely on a GPS for your navigation. Why? Well, it
may work well, but there are factors in which a GPS is becomes worthless. Like
when the batteries die, or in the unlikely (but possible) event of a system
outage. The GPS can save you time and frustration by easily telling you the
distance and direction of a waypoint, but it can never replace common sense.
Always have a primary, and backup method (maps, compass, and a knowledge of the
land) for navigation. What
should I look for in a GPS
receiver?
Like I mentioned earlier, most receivers have matured on the technical
level. For example, most current receivers can receive up to 12 satellites. Why
not more? Because you can hardly “see” more than nine! Remember, half the
satellites are on the opposite side of the Earth. So what are the features and
options? The most basic receiver will provide your latitude and longitude
(position), speed, direction, basic navigation, plotting functions, and named
waypoints. In my experience, this is all you need. However, newer receivers are
coming out with color LCD displays, and built-in maps. Obviously, color can’t
be beat, especially if you plot your waypoints and path. Built-in mapping
generally includes street-level mapping details, which are good for finding
addresses, but are usually unnecessary in the field. Some units will include
mapping software on CD-ROM that will let you download info into the receiver for
trips. There are also aviation units, which include airport and navigation
information, but these are very expensive. Anything
else?
First off, I own two GPS units. I have an older Lowrance
GlobalNav Sport (which was a very slow five-channel), and a Lowrance GlobalNav
12. I used to have the Eagle version, but I found that the 12 VDC input was
incompatible with the 24 VDC electrical system of a Cessna 172, and blew it up!
I use my 12 channel for hunting, hiking, driving, and flying. For hunting, we
will usually set treestands, trail intersections, and camp as waypoints. With
this data, we can plot a map of our hunting area, and know where we are,
compared to other locations or camp. For hiking, I will set the truck and
trailhead locations, and usually not use it at all, unless I get a little
disoriented. In my opinion, owning a GPS should be mandatory for all hikers. You
can get them for as low as $90. How often have you heard on the news about lost
hikers dying of exposure, when they were only a couple of miles from their cars?
While my GPS has no map function, I will use it for driving, especially if I
want to know how far from home I am. It is also good to have while scouting out
hunting locations because you can have an idea how far (and what direction) from
camp you are.
For aviation, GPS can be either a big help, or a confusion while flying
VFR. Most aviation units are very expensive, because they have the airport and
navigation data built in. However, the databases are only good for so long, and
then you have to upgrade them. I enter the lat/long coordinates directly into my
GPS and name them as waypoints. I also enter VOR/NDB data. You can get all this
data in the Airport Facility Directory. While flying, it is nice to know the
distance and heading from an airport, but when the tower asks you for your
position, they prefer visual landmarks and approximate heading/distance reports.
Controllers are not too keen on hearing that Cessna 99X is 12.2 miles at 147o!
Selective Availability: SA was an intentional error signal that threw off
the accuracy of a civilian GPS. While the accuracy was okay, you could still be
off by up to 300 ft! SA was to prevent a terrorist from aiming a missile at the
White House and using GPS technology to guide it. Well, military GPS units were
not affected by SA, and as the explosion of GPS use in the civilian world
mandated 30 foot accuracy, it was found that SA was not really necessary. A
missile could still do plenty of damage if it exploded nearby, and civilian
mapping and surveying required accurate GPS signals. So, in late May 2000, Bill
Clinton signed the Executive Order which allowed the termination of Selective
Availability. My GPS now reads out in feet when you get close to a waypoint! Got
a good idea for using your GPS? Let us know! William Noll, Hunting Editor |
|
|