Geoscience Reference
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altitude registration was assumed equal to 100m. At altitudes below 500m the
true aircraft altitude was used because the distance between the aircraft and
surface was measured with high accuracy with the radio altimeter. There was
a gap between these two scales caused by the Earth's surface altitude above sea
levelandbythevariationsofpressureprofileoftherealatmospherecompared
with the standard model (Standards 1981). This gap was determined through
the comparison of the altimeter and radio altimeter registrations and was ac-
counted for while forming the common altitude scale (by the pressure) for the
irradiance profiles.
For accomplishment of the soundings, the areas of the Ladoga Lake, the
Kara-Kum Desert (Turkmenistan, near the town of Chardjou) were chosen.
This choice was conditioned by the demands of surface uniformity mentioned
in the previous section and by the airports situated in the neighborhood as
well. Correspondingly the soundings were carried out above three types of
surface: snow (on the ice of the Ladoga Lake), water (the Ladoga Lake) and
sand (the Kara-Kum Desert).
The most complicated stage of the secondary data processing was the initial
one, i. e. the preliminary analysis and correction of the irradiance spectra.
First, it was connected with the rather complicated conditions of the flights,
which caused themalfunctions of the equipment on board and the errors of the
registered spectra at some wavelengths. However, owing to the high scientific
value of the data (and owing to the high price of the airborne experiments) it
was inappropriate to exclude the whole spectrum because of the errors at one
or several wavelengths. Hence, careful analysis of the errors together with the
spectra correction was needed. Besides, the flight conditions did not allow us
to realize the ideal sounding scheme as a whole; it caused the necessity of data
correction while taking into account the deviation of the measuring procedure
from the ideal scheme.
The attempts to create the universal algorithm of error correction of the
measured spectra failed because of a huge variety of concrete errors. They
were revealed and removed by hand, using the visual interface of the database
described in the previous section. This algorithm was applied to observations
in an overcast sky. However, applying this approach to the spectra of the clear
atmosphere needed too much time because there were many more of these
spectra. Just this obstacle was the reason why a significant volume of the
data measured in 1983-1985 was processed only at the end of 1990th when
a system for fast processing was created. The basis of the system was the idea
of the semiautomatic regime . The data analysis was accomplished without an
operator but after the error was revealed the passage to hand processing in the
interactive regime occurred. In addition, the program code suggested different
solutions to the operator.
The brief description of the proposed system of spectra processing with the
detailed consideration of the approaches and schemes that could find a wide
application in the preliminary analysis of the results of solar radiances and
irradiances measurements are presented below.
At the first stage, the errors like an overshoot together with breaks of the
spectrum parts are revealed using the logical analysis of every spectrum. The
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