37
ATMOS 41W
When powered on, the ATMOS 41W measures the air temperature once every 3 s and records
the instantaneous values. At the end of the measurement interval, the ATMOS 41W outputs
the average of the instantaneous values measured during that measurement interval and the
minimum and maximum instantaneous air temperature measurements.
NOTE: The ATMOS 41W body and especially the temperature sensor should not be painted or coated.
Temperature sensor
Figure 20 Temperature sensor
AIR TEMPERATURE THEORY
The ATMOS 41W uses an energy balance correction to adjust measured temperature to
actual air temperature according to
Equation 3
.
Equation 3
T
corr
=
T
uncorr
−
α
S
S
t
c
p
k u / d
⎛
⎝
⎜⎜
⎜⎜
⎜⎜
⎞
⎠
⎟⎟⎟
⎟⎟⎟
where:
α
s
= the absorptivity of the surface to solar radiation
S
t
= the total solar radiation measured
c
p
= 29.3 J mol
–1
C
–1
, k is a constant
u
= the wind speed
d
= the characteristic dimension
Although these values can be assumed, some (
α
s
and
k
) were optimized using a Levenberg
Marquardt Least Squares analysis. Optimal air temperature was obtained using an Apogee
TS-100 Aspirated Radiation Shield. Data were collected over several weeks and final values
are shown in
.
NOTE: A maximum value optimization for
S
t
was added because radiation values higher than that cause the corrected
temperature to deviate from actual values more than when a maximum
S
t
was used.
