Spectral Measurements of Solar Irradiance and Radiance in Clear and Cloudy Atmospheres - Short-Wave Solar Radiation in the Earth's Atmosphere - page 122

3.6
Ground and Satellite Solar Radiance Observation in an Overcast Sky

This section presents brief information about the experiments whose results
have been used for the retrieval of the cloud optical parameters. There are
groundobservationswith the spectral instruments described invarious studies
(Mikhailov and Voitov 1969; Kondratyev and Binenko 1981; Radionov et al.
1981; Gorodetskiy et al. 1995; Melnikova et al. 1997) and satellite observations
with the POLDER instrument on board the ADEOS satellite (Deschamps et al.
1994; Breon et al. 1998).

3.6.1
Ground Observations

Thegroundobservationshaveincludedthetransmittedspectralradiancemea-
surements for several viewing angles. The conditions of their accomplishment
arelistedinTable3.3(thenumerationinthetablecontinuesTable3.2).The
first experiment was performed under overcast conditions at the drifting Arc-
tic station SP-22 on the 13th August and on the 8th October 1979 (Radionov
et al. 1981). The measurements had been carried out in the spectral interval
0.35-0.96 µ µ m, but the results were processed only at

11 spectral points in each spectrum. The error of the transmitted radiancemea-
surements was evaluated within 3% (Mikhailov and Voitov 1969; Radionov et
al. 1981). There were extended, horizontally homogeneous thick clouds during
the experiment.
The second experiment was accomplished under the overcast condition in
St. Petersburg's suburb on 12th April 1996 (Melnikova et al. 1997) with the
spectral instrument, constructed by the authors of the study by Gorodetskiy
et al. (1995) on the basis of the CCD matrix detector and with spectral res-
olution 0.002

m with resolution 0.001

µ µ m (Gorodetskiy et al. 1995).

Use of this spectrometer allowed registration of the signal within the spectral
ranges 0.35-0.76

m and spectral range 0.35-0.76

µ m simultaneously in every spectral point. The instrument

was characterized with small size and was PC or Notebook compatible thus,
it was convenient for field observations, provided the diminishing of some
observational uncertainties and allowed the initial data processing at once.

Tab l e 3 . 3 . Details of the ground radiative experiments

µ 0 ϕ

, ◦ ND te

No. Experiment A s Other conditions

11 Arctic drifting

station SP-22

0.500 85 13 August 1979 0.60 Surface is wet snow

12 Arctic drifting

station SP-22

0.275 85 08 October 1979 0.90 Surface is fresh snow

13 Petrodvorets 0.620 60 12 April 1996 0.70 Surface is fresh snow