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and 180
Figure A.2. Area (stippling) for which the between-beam angle
.
In this figure the two radars are located at x ¼ d and y ¼ 0 (not at x ¼ 0 and x ¼ x 2 , and
y ¼ 0 as in Figure A.1) (from Davies-Jones, 1979).
lies between
tion about the component of the wind normal to the ''baseline'', which is defined
by the line connecting the locations of two adjacent radars. Similarly, if the two
beams are nearly parallel to each other, so that the between-beam angle
approaches 0 , there is also no information about the component of the wind
normal to the radar beams. The optimum situation is one in which the radar
volume is positioned such that the between-beam angle is 90 . For targets very
close to the baseline, the between-beam angle approaches 180 ; for targets far
from and normal to the baseline, the between-beam angle approaches 0 .Itis
clear that the target must be located in certain restricted areas with respect to the
radars. For fixed site radars, one can only hope that a target will pass through the
optimum region. The length of the baseline is chosen so that target scatterers lie
within the acceptable between-beam angle to minimize errors and to ensure that
the spatial resolution of the radar volume is sucient to map out the wind field
for spatial scales that must be resolved.
During field operations using mobile radars, one can position the radars so
that the target will pass through the optimum region, but often this cannot be
done when the road network is inadequate. Airborne radars do not have this
 
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