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| Titel |
Preliminary 4-band colour photometry of the Earth, using Earthshine observations. |
| VerfasserIn |
Peter Thejll, Chris Flynn, Hans Gleisner, Torben Andersen, Ahmed Darudi |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079211
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| Zusammenfassung |
| The terrestrial radiation budget determines, and depends on, climate
and is therefore valuable to study empirically, as it gives insights
into the state of the climate system as well as our own theoretical
understanding of climate processes and modelling skills. The long-wave
and shortwave components of the budget are typically observed with
quite different technologies. From space, shortwave outgoing fluxes are
commonly derived from satellite image data. The long term stability
of these is known to limit the accuracy to about 1%. Precision can be
much higher at a given moment, but the lack of high accuracy in the long
terms limits the insights that can be had from satellite-based studies
of the net shortwave flux.
Better long term accuracy is promised by methods based on using the
Earthshine intensity as a proxy for terrestrial shortwave outgoing
fluxes. We have designed and built an Earthshine observation system,
and operated it for 1 year at the Mauna Loa Observatory on Hawaii. We
present preliminary results from this observing period. The data were
obtained in 4 broad photometric bands and we can present the Johnson B-V
colors of the Earthshine, along with a color index similar to the NDVI
index commonly used to investigate the presence of vegetation on Earth
in satellite images.
Scattered light has to be removed from the data before analysis, and we
show results following two independent paths for coping with this.
While Earthshine observing methods may be precise at any given moment,
and more accurate in the long run - since it is a self-calibrating
method - the overall signal to noise ratio is dominated by the natural
variability of Earth's reflectivity, and data must be gathered, just
as with satellites, for a long period before the potential benefits
of Earthshine observations are felt. The Earthshine technique remains
much less expensive than satellite technologies and can be a valuable
independent means of complementary data. |
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