Spectral Measurements of Solar Irradiance and Radiance in Clear and Cloudy Atmospheres - Short-Wave Solar Radiation in the Earth's Atmosphere - page 97

Fig. 3.8. Vertical profile of the spectral semispherical solar irradiance from the results of the
airborne sounding 16th May 1984. Water surface, solar zenith incident angle 43 ◦
extinction of the upward radiation is weaker than its increasing caused by
backscattering of the downward radiation.
As has been mentioned in the previous section not all spectrum points are
independent and hence informative after the secondary processing. Figure 3.9
illustrates only the informative points of the same spectra as Fig. 3.6 does.
In practice, the real number of the informative points differs very much for
different spectra that seems to link with non-ideal weather conditions together
with the errors during the registrations.
The spectral region is excluded from the further processing when there are
lessinformativepointsinit.Thus,Fig.3.9demonstratesasoundingofhigh
quality. An example of a “bad” sounding is shown in Fig. 3.10 that is analogous
to Fig. 3.8 excluding the non-informative points.
The uncertainty of measurements is themost important characteristic vary-
ing strongly in different soundings. Figure 3.11 shows the minimal relative
standard deviation over all realizations for downwelling and upwelling irradi-
ances. It is easily seen from the comparison of the relative standard deviation
with the initial values (Table 3.1) that the statistical processing significantly
improves the accuracy of the results.
The vertical profiles of the spectral albedo of the “atmosphere plus surface”
system characterizing three types of the surface are presented in Fig. 3.12.
Thefiguredemonstratestheresultsofthesoundingsabovethesandsurface
(16 October 1983) - solid lines, above the snow surface (29 April 1985) - upper
group of dashed lines, and above the water surface (16May 1984) - lower group