http://www5.ncdc.noaa.gov/plwebapps/plsql/ssmimain
Auswahl folgender Parameter: Global - Wetness - Full Field
http://www5.ncdc.noaa.gov/plwebapps/plsql/ssmigetimage/
Thema: Oberflächenwasser pro Monat in % (Liquid Water observed
on the surface per months in %)
Beobachtungszeitraum vom Dez. 1997 bis Nov. 1998
Originalgröße der Gesamtbilder: 792 * 612 Pixel, nach
der Bearbeitung Kartenausdehnung 654 * 338 Pixel
Zur Erläuterung der Karten soll folgende Intensitätsskala dienen:
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How to interpret the maps:
The products presented on the National climatic Data Center (NCDC) web page
include full and anomaly fields for land surface temperature, wetness, and snow
cover (peer reviewed references are provided below). These climate products
are derived from the Special Sensor Microwave Imager (SSMI), a polar orbiting
satellite with global coverage. The wetness products represents the percentage
of the radiating surface that is liquid water. Since this spectrum of microwave
radiation can penetrate vegetation, the radiating surface can be vegetation
and/or the ground. Liquid water can originate from recent rainfall, melting
snow, ponding and/or flowing surface water, and/or irrigated fields.
Surface water does necessary equate to soil moisture, since the signal does
not penetrate any appreciable depth below the surface. Ignore the wetness and
snow cover anomalies over Glacial ice (Greenland and Antarctica), since the
microwave emission originating deep within the ice pack can product some unique
(false) signatures. All three of the above climate products have been developed
by the National Environmental Satellite and Data Information Service (NESDIS)
at two cooperative centers NCDC and Office of research and Application (ORA).
Satellite measurements offer a possible way to fill in the data voids and obtain
a complete map of surface temperature, surface wetness and snow cover over the
entire globe. To accomplish this, we identify numerous surface types and make
dynamic adjustments for variations in emissivity. Training data sets were used
to define the relationship between the seven SSM/I channels and the near surface
temperature. For instance, liquid water on the surface reduces emissivity; therefore
we developed an adjustment to correct for this reduction. Other surface types
(e.g., snow, ice, and deserts) as well as precipitation are identified, and
numerous adjustments and/or filters were developed. The Global and U.S. networks
of first order and cooperative stations, quality controlled by NCDC, serve as
validation.
The surface water depresses the emissivity and therefore dynamic adjustments
are necessary to derive the correct surface temperatures, and this emissivity
reduction provides the signal for the surface wetness index. Multiply frequencies
available on the SSMI instrument have different responses to the liquid water
on the land, and this response across the microwave spectrum indicates the percentage
of the ‘radiating surface’ that is water. Once this percentage is
known, we can use the emissivity of water and dry ground to make the correction
for the actual surface temperature. The snow cover product identifies the frequency
of snow observed on the surface, and it is presented as a monthly percentage.
This product relies on the fact that snow reflects high frequencies more than
low frequency, known as a scattering signature. Therefore when a scattering
signature is observed and false ones removed, the satellite observes the global
distribution these derived products as it continues to rotate between the poles
14 times each day.
Die einzelnen (bereits ausgeschnittenen) Karten wurden im WWW Gif Animator zu einem animierten GIF zusammengestellt. Dabei mußte auf die Reihenfolge der einzelnen Images geachtet werden.