
82-6 Environmental
measured for the return path. In the absence of wind, the transit times are equal; but in the presence of
wi
nd,
th
e
wi
nd
co
mponent
al
ong
th
e
di
rection
be
tween
th
e
tr
ansmitter
an
d
re
ceiver
a
ects
th
e
tr
ansit
ti
me
. r
ee
su
ch
pa
irs,
mo
unted
12
0°
ap
art,
en
able
ca
lculation
of bo
th
th
e
wi
nd
sp
eed
an
d
di
rection
.
He
aters
i
n
th
e
tr
ansducer
h
eads
m
inimize
pr
oblems
wi
th
ic
e
an
d
sn
ow
bu
ildup
. e ab
sence
of mo
ving
pa
rts
e
liminates
t
he
n
eed
f
or
p
eriodic
m
aintenance
.
82
.2.4.3
Wi
nd Direction
Wind direction sensors are generally some variant of the familiar weather vane. Sensitivity is main-
tained
by co
nstructing
th
e
we
ather
va
ne
to ro
tate