
82-11Meteorological Measurement
e extinction coecient (k) is related to visual range (VR) by VR = 5/k (km). VR measurable by such a
system lie between about 0.3 and 60 km. Figure 82.5 shows the visibility sensor used in the ASOS net-
work
. A x
enon
ash
l
amp
s
ource
i
s
u
sed
w
ith
t
his
s
ystem
.
82
.2.7.2
T
ra
nsmissometers
ese
m
easure
t
he
a
ttenuation
o
f
a l
ight
b
eam
to d
etermine
v
isibility
.
82.2.8 Lidar Measurements
Lidar is optical radar in which a laser emits pulses of electromagnetic radiation. Scattered radiation that
returns to an optimally tuned detector at the laser site for observation is called echos. e time from emis-
sion
of th
e
pu
lse
to