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| Titel |
Estimates of radiance reflected towards the zenith at the surface of the sea |
| VerfasserIn |
E. Aas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 6, no. 4 ; Nr. 6, no. 4 (2010-10-05), S.861-876 |
| Datensatznummer |
250003677
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| Publikation (Nr.) |
 copernicus.org/os-6-861-2010.pdf |
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| Zusammenfassung |
| Remote sensing of water colour by ship-mounted sensors represents an
important tool for the validation of satellite products and the monitoring
of water quality. The recorded radiance from the sea has to be corrected for
the surface-reflected radiance from sun and sky in order to obtain the
water-leaving radiance. Here the simple case of radiance reflected towards
the zenith is studied. A set of observed sky radiance and solar irradiance
data from Oslo has been used together with a Gaussian slope distribution for
the sea surface in order to estimate the reflected radiance. The spectral
range studied is 405–650 nm, the solar zenith angles are in the range 37°–76°,
and the wind speeds are up to 10 m s−1. The analysis of the
results show that the reflected radiance has to be separated into three
contributions: sky radiance and sun rays reflected at the foam-free surface
and irradiance reflected by whitecaps and foam. It is then demonstrated that
by using four input values, namely the downward irradiance, the sky radiance
from the zenith, the solar zenith angle and the wind speed, it is possible
to obtain by simple expressions estimates of the reflected radiance that
only differ from the former calculated values by relative errors of less
than 5%. The analysis also indicates that for the spectral range studied
neither the water-leaving radiance nor the surface-reflected radiance can be
disregarded relative to the other one in the Case 2 waters of the
Oslofjord-Skagerrak area. The results form a first step towards the study of
reflected radiance in viewing angles differing from the nadir direction. |
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