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October 2016
31
3.3.3 How to do ?
To perform a Langley type calibration, choose a day of good and stable weather
to have a constant optical thickness throughout the day. That is to say, a clear sky
without clouds above sea level, without wind.
The sites in altitude, away from cities offer more easily this type of sky. We must
stay on the same site for all measurements.
So take action one or two hours after sunrise until solar noon least the place.
(Red Sun is going to pale yellow Sun on the previous graph).
Continuing the afternoon, we get the "down" curve, which theoretically merges
with the "rising" curve. This can be a weather stability index of the day.
It is not recommended to perform calibrations during winter because the sun is
low on the horizon, the air mass is not enough to approach 1 (over 2.5 on the
winter solstice so that it reaches 1.07 at the summer solstice for example in
Toulouse, in the south of France).
During the measuring morning of measurements, you should take at least five
series from 3 to 5 measurements.
Here are measurements taken August 21, 2013 near Toulouse in blue color. The
data were gathered in a spreadsheet and the equation of the trend line has been
displayed, allowing us to calculate the CN
0
parameter.
CN
0
_465 = exp(
8,1503851986
) => CN
0
_465 =
3465
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12:09:00
10:40:00
10:01:00
08:51:00
08:17:00
07:55:00
07:19:00
07:07:00
06:50:00
06:33:00
06:08:00
06:00:00
06:00:00
05:40:00
Содержание CALITOO
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