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| Titel |
Radiometric calibration of airborne laser scanning data: case study rockglaciers |
| VerfasserIn |
Hubert Lehner, Christian Briese, Rudolf Sailer |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055935
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| Zusammenfassung |
| In the last years airborne laser scanning (ALS) has become a state-of-the-art technology for
topographic data acquisition. Classification of the 3D point cloud into different categories
(e.g. ground, vegetation, and buildings) is one of the main challenges of ALS research in
order to use the point cloud for further applications. So far, most classification techniques
consider just the local geometry of the 3D point cloud or parameters which can be derived by
analyzing the neighborhood relationship of the point cloud or the number of echoes per
emitted laser shot.
Discrete echo systems directly deliver the amplitude (often referred to as intensity) of the
received signal in addition to the 3D position of the echo. In contrast to these systems
full-waveform laser scanners provide after Gaussian decomposition next to the amplitude also
the width of each echo. These physical observables describe the return power of the target
and can thus give information about the target without any analysis of the geometry of the 3D
point cloud. However, these observables are influenced by many different factors (e.g.
range, angle of incidence, surface characteristics, atmosphere, etc.). Therefore, the
comparability of these attributes between different sensors, different flight missions or
even different flight strips within one flight campaign is poor. The usability of ALS
amplitude data for landcover classification could already be shown, whereas the full
potential of the radiometric observables is yet not completely explored due to the
difficulty of calibrating them into physical units. By using reflectance values of natural
surfaces within the area of interest, e.g. determined with a RIEGL reflectometer and
Spectralon®Â targets, radiometric calibration enables to convert the amplitude and echo width
into absolute radiometric values which describe the characteristics of the observed surface.
With this procedure, classification becomes independent of sensor and mission
parameters.
Within this contribution the practical benefit of radiometric calibration will be presented
based on ALS data acquired in September 2009 with the Optech ALTM 3100 system of the
active rockglacier Hochebenkar, which is about 4.3 km south of Obergurgl (Ötztal Alps,
Tyrol, Austria). The monitoring of glaciers and permafrost (in particular rockglaciers) supply
important information on climate change impacts on the cryosphere. The results of the
remote monitoring of rockglaciers and permafrost are relevant for scientist (e.g. climate
change impact research, natural hazard research) and in case of permafrost related hazards for
stakeholders and public authorities too. In mountainous areas it can especially be shown that
the effect of different ranges due to the topography of the observed area effects the amplitude
measurements. As already mentioned before, radiometric calibration enables to gain
absolute radiometric values, which can then be used for various tasks, such as for
discrimination of different surface types. Moreover they enable to document the status of the
glacier over the years, in case of continuously repeated ALS campaigns as scheduled
within the ACRP project C4AUSTRIA (Climate Change Consequences on the
Cryosphere). |
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