Geoscience Reference
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through the accuracy of the lamp SI-8 signal measurements. It was 15% in the
UVand10%intheVDandNIRspectralregions.
To control the stability of the instrument sensitivity during the observation
the special internal standard was installed inside the instrument - an incan-
descent bulb with a stabilized supply. During the observation, the internal
standard spectra were monitored (about every 5 min). To correct the possible
deviations of the sensitivity, these spectra were compared with the average in-
strument spectrum, which had been registered during the calibration. For this
purpose, after every internal standard spectrum registration the mean ratio of
this spectrum to the average instrument spectrum was obtained over the spe-
cially chosen intervals (each interval contained 10 wavelengths) within every
spectral regionof the instrument (UV, VD, NIR) toprovide three correcting fac-
tors . Further, all measured spectra of the solar irradiances or radiances, which
followed this internal standard spectrum, were divided by these correcting
factors.
The external standard spectra similar to the internal ones (the spectra of
theincandescentbulbinstalledoutsideoftheinstrument)wereregisteredto
correct for a factor of the transparency variations of the opal glass (due to
contamination) during the measurement process together with the difference
ofthetransparenciesoftheupper(fordownwardradiation)andlower(for
upward radiation) opal glasses. During the airborne observational process,
the recordings of the external standard through the opal glasses of the light
conductor were being accomplished on board of a landed aircraft. Analogously
to the above-considered procedure of obtaining the correcting factors, the
curve to correct for a factor of the transparency variations was plotted from
theratiooftheexternalstandardspectratotheSI-8lampspectrum,registered
through the light conductor.
The computer code of the initial processing, whose last version was realized
on PC, allowed the fulfilling of all initial procedures (including the graduation
and calibration) in an interactive regime, with different levels of researcher
interference to the process: from step-by-step control to an automatic regime
directly outputting the desired spectra (Vasilyev O et al. 1995).
Nowadays all the obtained spectra forms a computer database of the Air-
borne Spectral Radiative Observations (ASRO product) containing the obser-
vational results since autumn 1983 and including about 30,000 spectra. Every
spectral file contains all necessary information concerning the observational
process (date and time of the registration, altitude of flight, solar zenith angle,
geographical coordinates, etc.) essentially simplifying and accelerating further
dataprocessing.Thisdatabaseisalsoprovidedwithaflexibleinterface,allow-
ing different procedures either with a separate spectrum or with groups of
spectra, e. g. table output, the examination of plots, interactive regime correc-
tion, arithmetic operations with spectra (addition, subtraction, multiplying,
division), smoothing, approximation with polynomial, elementary statistics
(computing the mean value and the variance), etc.
Additional secondary processing of the obtained radiances and irradiances
is necessary for determining the spectral reflectance characteristics of the sur-
faces and the values of radiative flux divergence in the atmospheric layers,
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