NRI Grazing Land On-Site Data Collection
(03/23/20011) B-28
The estimate tends to be lower than reality. NCGC user experience indicates
that the estimate is anywhere from 25 to 50 percent too low. For example if
the estimate reads “15 feet” then the actual positional error is most likely
between 19 and 23 feet.
°
The signal strength bars. There are five gradations of strength in this data field.
Most, if not all, of the satellites the Map 76 is using for position computation
should be at the fourth level or higher. If they are not you might try:
Holding the receiver higher. Your body is very good at masking GPS signals.
Holding the receiver at arms length. This further reduces body masking.
Facing toward the southwest. This is the part of the sky with the highest
intersection of GPS orbital planes.
Facing toward the most unobstructed part of the sky. This will help you
reduce terrain masking.
Using an external antenna. An external has better gain (reception) than the
antenna in the receiver. It also can be easily mounted (using a backpack and
an antenna bar) at or above head level so you don‟t wear your arm out.
Paying attention to your environment. Are you standing on pavement, a rock
field, or next to a rocky bluff or cliff? If so you are in a multipathing
environment and the GPS receiver is receiving the same signal from several
different directions.
Try using a ground plane, a metal disk that mounts on top of the antenna bar.
Its diameter should be a little bit larger than the external antenna.
If you are trying to navigate to a point located in a high multipathing area then
you can stand outside the area – determine the distance and direction to the
point – then step off the remaining distance in the correct direction.
Navigation – Localizing the Target
Approach the target point while keeping an eye on the “Distance” field you have set
up on the Pointer Page. Remember that the point of the arrow should be aligned with
the bar at the top of the compass rose – this will indicate the proper direction.
When you see the distance decrease then suddenly increase you have gone past the
point.
Stop immediately and watch the Distance field.
Take two to several steps in the direction you just came from. Watch the alignment
of the arrow with the bar. Adjust your direction so they are aligned.
Continue to take two to several steps in the direction indicated by the arrow point and
vertical bar. Try to come as close as possible but don‟t spend a lot of time. You are
using autonomous (without corrections) GPS so your positions will be less precise.
