In the field, the hiker needs a way to express the
direction to an object or the direction of intended travel. The two terms most commonly used for such
expression are bearings and azimuth.
Both are described by units of angular measurement.
Azimuth is the common term used by the military in land
navigation.
Bearing is the term most frequently used by those
recreating in the backcountry. Bearing
will be used during the rest of this discussion. Bearing is the horizontal angle measured
clockwise from North.
The degree is the common unit of measurement of a
bearing. A degree can be broken down
into the following terms:
A
circle = 360°
1
degree (1°) = 60 minutes
1
minute = 60 seconds
Thankfully, most direction information is expressed
simply in degrees. For example, the
direction to a destination calculated by a Global Positioning System (GPS)
receiver will be stated in degrees.
Degrees will always be described in relationship to a
circle and a starting point. A circle is
comprised of 360 degrees; check your compass dial to confirm. In land navigation, the starting point is
from north. Commonly, the angular
measurement is calculated from one of three options. These are True North, Magnetic North and
Grid North.
True
North is the direction from any point on the globe to the North
Pole. All lines of longitude are lines
that run true north and south. Angular
measurement is calculated from the starting value (0°) clockwise to the desired
direction. For example, east has a
direction of 90°. (The best practice is
to state the bearing in three digits, thus, 90° becomes 090°.) Bearings measured from the North Pole are
referred to as degrees true.
Magnetic
North is the direction to the Magnetic North Pole. Note that Magnetic North and True North are
not the same. The angular difference
between True North and Magnetic North is known as declination. (For more information read my post Declination). The
angular measurement is measured clockwise from the magnetic north arrow to the
desired direction.
Grid
North for the recreating hiker is in relationship to Universal
Transvers Mercator (UTM) grid. The globe
is bounded by 60 UTM zones that stretch north to south. The central meridian of the UTM zone is
aligned to true north.
For the backcountry navigator, the simplest method is to
use bearings that are in relation to true north. In my navigation classes I suggest that
students “match the map” that will be used in the field. In most cases a map is oriented to the North
Pole. A GPS can be setup such that the
receiver provides direction information in degrees true. I also recommend consider the purchase of a
declination adjustable compass such as the Suunto M3 or the Silva Ranger. Though the magnetic needle always point to
magnetic north, the dial provides direction data in degrees true. Thus, both instruments (GPS and Compass) will
match the map.
No comments:
Post a Comment