Infrared radiometer experiments
CARRIAGEWAYS STATE MONITORING
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Several winter campaigns for the monitoring of the state
and temperature of the carriageway, dedicated to ice and
frost forecast, were carried out by the LOA in collaboration
with CIMEL Electronique and the Ministry of Transport. The
view above, shows the station of Pecquencourt ( Nord, 50
km of Lille).
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During the night of the 26 Feb, around 2h27, the spectral
signature of the carriageway suddenly changedwhile the sky
was clear as confirmed by the radiometric measurements.
So this signature change cannot result from clouds occurrence
- this is confirmed by the instantaneous and steady character
of this change. Indeed, the signature change results from
a damping of the carriageway, as indicated by the probe
of damping of the instrument. This must result from the
condensation of water (on the carriageway and the probe);
or most likely of frost deposit due to the negative temperatures
observed.
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A field blackbody is viewed by the radiometer, and its
direct temperature measurement with a platinum probe is
compared to its radiometric derivation.
The difference between both determinations is typically
0.1°C, representing the uncertainty of the radiometric measurements.
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SEA SURFACE TEMPERATURE MONITORING
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The radiometer was flown over the English Channel during
an experiment primarily dedicated to check its behavior
in airborne conditions. It measured the radiance at nadir
in order to determine the sea surface temperature.
The atmospheric correction was performed using a split-window
technique between channels N11 and N12. The retrieved temperatures
are compared to the temperatures from the satellite ATSR
(the field of ATSR seasurface temperature).
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DESERT DUST MONITORING : Comparison
between radiometer radiance values and theoretical simulations
Simulation
Using the Longtin desert aerosol model [Longtin
et al. 1988], a study [Pombo, 1996] was performed in order to
calculate theoretical values of sky radiance for different columnar
water vapor amounts. These values were represented according to
the integrated mass of aerosol (the curves with non-filled symbols).
Experimental radiometric data
Firstly we represented the experimental radiometric
values of sky radiance function of the aerosol optical depth (provided
by Sun photometric measurements). Then, using the same desert
aerosol model, we established a relation between this optical
depth and the integrated aerosol mass. Thus, we represented the
experimental radiance function of the integrated aerosol mass
(the filled symbols).
The radiometric data are in accordance with the
theoretical simulations and we observe a different behaviour of
the experimental points corresponding to different seasons: dry
(filled square symbols) and rainy (filled triangle symbols).
