INSTALLATION OF MONITORING STATIONS - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 64

180° 135°W 90°W 45°W 0° 45°E 90°E 135°E 180°

70°N 70°N

60°N 60°N

2 20

45°N 45°N

30°N 30°N

15°N 15°N

0°
15°S

1 10

0°

1 10

15°S

30°S 30°S

2 20

45°S 45°S

3 30
4 40

3 30

4 40

60°S 60°S

-90 -90
-100 -100

70°S

70°S

180° 135°W 90°W 45°W 0° 45°E 90°E 135°E 180°

Figure 5-1. Map illustrating magnetic declination for the world in 2004. Blue lines indicate
that magnetic north is west of true north, while red lines indicate the opposite. Source: US
National Oceanic and Atmospheric Administration.

If a correction from magnetic north is required, the local magnetic declination (in
degrees) must be established. This correction can be found on topographic or isogonic
maps of the area (an example is provided in Figure 5-1). How the correction is applied
depends on whether magnetic north is to the west or east of true north. To the east,
the declination is expressed in degrees west of true north, and the bearing toward
true north therefore equals the declination. To the west, the true north bearing is 360 ◦
minus the declination. In both cases, the true north bearing must be added to the
direction relative to magnetic north to obtain the direction relative to true north. For
example, suppose a sensor boom has an orientation of 150 ◦ from magnetic north. If
the local magnetic declination is 15 ◦ W, then the boom orientation from true north is
135 ◦ . If, however, the magnetic declination is 15 ◦ E, then the boom orientation from
true north is 165 ◦ .

5.6 TOWER INSTALLATION

5.6.1 New Tilt-Up Towers
Tilt-up towers can be erected almost anywhere, but the task is much easier if the
terrain is relatively flat and free of trees. If the tower is erected on sloping or uneven
ground, the guy wires may need to be adjusted often as the tower is raised. If the tower
is erected in a wooded or otherwise obstructed area, there must be a clearing around
the tower, which should be large enough for the tower to lie flat and the guy wires to
be anchored. The required clearing for guyed tilt-up towers can be large. For example,
a 60-m tilt-up tower is guyed in four directions from the tower's base. The outermost