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| Titel |
Validation of Land Surface Temperature Products and Site Characterisation with Ground Based Radiometric Measurements |
| VerfasserIn |
Frank Goettsche, Folke Olesen, Annika Bork-Unkelbach |
| 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 |
250072789
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| Zusammenfassung |
| Land Surface Temperature (LST) is an important quantity for the energy and water exchange
between the earth’s surface and the atmosphere and, therefore, an important parameter of
many environmental models. LST is derived operationally from several space-borne sensors,
e.g. the Moderate Resolution Imaging Spectroradiometer (MODIS) on EOS-Terra and the
Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat Second
Generation (MSG) and AVHRR onboard NOAA and EPS satellites. Ground based validation
of LST and Land Surface Emissivity (LSE) is largely complicated by the spatial scale
mismatch between satellite sensors and ground based sensors: areas observed by ground
radiometers usually cover about 10 m2, whereas satellite measurements in the thermal
infra-red typically cover between 1 km2 and 100 km2. Therefore, validation sites have to be
carefully selected and need to be characterised on the spatial scale of the ground radiometer
as well as on the scale of the satellite pixel. The permanent validation station near
Gobabeb, Namibia, is one of KIT’s four dedicated LST validation stations. Gobabeb is
located on vast and flat gravel plains (several 100 km2), which are mainly covered by
coarse gravel, sand, and desiccated grass. The plains are highly homogeneous in
space and time, which makes them an ideal site for validating a broad range of
satellite-derived products. However, for reliable product validation the effect of
the small scale variation of surface materials (e.g. dry grass, rock outcrops) and
topography needs to be closely characterised. Using a mobile radiometer system,
several field experiments were performed during which the radiometer was driven
along tracks of 20 km to 40 km length through the gravel plains. The results show a
high level of homogeneity and a stable relationship between station LST and LST
determined along the tracks from the mobile measurements with a small bias of about
0.4°C. LSEs of the dominant surface cover types at Gobabeb were obtained with
the so-called ‘emissivity box method’, which consists of a sequence of thermal
infrared radiance measurements and employs a box with highly reflective inner walls
to control the radiation from the environment. The in-situ LSEs for Gobabeb are
compared to LSE products obtained with different operational algorithms from MODIS
and SEVIRI data. Finally, the monitoring capability of the validation stations is
demonstrated with a 5 year time series of LST derived operationally by the Land
Surface Analysis – Satellite Application Facility (LSA-SAF) from MSG/SEVIRI data. |
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