Page 129 - Fluid Power Engineering

106 Chapter Six

FIGURE 6-17 Picture of the Nomad TM SODAR unit. Size of the unit is 2 m ×
2m × 2 m and weighs between 350 and 450 kg. (Photo (copyright) Justin
Arcangeli. Courtesy Second Wind Inc.)

SODAR unit. Light Detection and Ranging (LIDAR) is based on shift
in frequencies because of reflection of light rays from small aerosol
particles in the air. Figure 6-18 is a picture of a LIDAR unit.
SODAR 9,10 works with three or five beams that are generated from
an array of speakers. The three beams measure the x, y, and z com-
ponents of wind speed in a volume of air. The x and y components
are measured by beams along the x and y axis at an angle of 10 to 20 ◦
from the vertical axis. The Doppler frequency shift is proportional to
the wind speed aligned to the path of the sound wave, which yields
the x, y, and z component of wind speed.
LIDAR uses light instead of sound and relies on the same Doppler
shift principle. However, in this case, the radiation is scattered by
aerosol particles like dust, moisture, and others.

Pros and Cons of Remote Sensing for Wind Measurements
The advantages of remote sensing compared to met-towers are
numerous: 11

Ability to measure wind speed at heights higher than “eco-

nomically” feasible by met-towers
Ability to measure over large range of heights from 40 to

200 m
Ability to measure wind shear directly over a large range of

heights
Ability to measure the vertical component of wind speed