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| Titel |
Sensitivity in the Correction of Long-Range Ground-Based Thermal Data. |
| VerfasserIn |
Anson Hancock, Mike James, Gaetana Ganci, Andrew Harris |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126918
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| Publikation (Nr.) |
 EGU/EGU2016-6714.pdf |
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| Zusammenfassung |
| Ground-based thermal remote sensing is a valuable tool for the study and monitoring of
volcanoes and their hazards. However, permanent monitoring installations often require the
camera to be positioned at relatively long ranges from the target (i.e. >1000 m). These
types of long-range deployments have been seldom analysed quantitatively due
primarily to factors such as atmospheric attenuation and across-image variations in
the target path-length resulting in substantial uncertainty in the derived surface
temperatures.
Here we examine the sensitivity of measurements at three different apparent temperatures
(400, 500 and 600 K) to uncertainty in the atmospheric conditions and type of path for the
INGV-Catania (Etna, Sicily) permanently installed thermal camera. The camera is
located at Mount Cagliato at an elevation of 1154 m asl and looks to the summit
area at ∼3000 m asl, over a distance of ∼8.5 km. Analysis was carried out using
MODTRAN to calculate atmospheric transmittance and upwelling radiance values for the
different scenarios. We then calculated corrected surface temperatures by applying an
atmospheric correction using two different temperature-to-radiance methods: a
top-hat wavelength integrated based method supplied by FLIR Systems in their
ThermaCam Researcher software and a mid-wavelength value method using the Planck
equation. Results indicate that calculated surface temperatures between the two
methods differ by as much as 382.5 K over a path-length of 8.5 km. Over path lengths
between 1 and 8.5 km, changing the atmospheric temperature to 288.15 (15 oC),
293.15 (20 oC) and 298.15 K (25 oC) resulted in increases in calculated surface
temperatures of 1.7–72.4 K using the FLIR top-hat method and 1.4–205.5 K using the
mid-wavelength method. For relative humidities of 40, 50 and 60 %, increases in
calculated surface temperatures of 1.0–58.7 K and 1.0–148.9 K using the FLIR
top-hat and mid-wavelength methods, respectively. We also found that calculated
surface temperatures differed by up to 69.9 K for an apparent temperature of 600 K
with the use of the MODTRAN ‘Rural, Visibility = 23 km’ aerosol model over a
path-length of up to 8.5 km. We were unable to get MODTRAN’s slant-path option to
work correctly for the oblique geometry characteristic of terrestrial cameras. As a
practical alternative, we propose the use of multiple stacked horizontal sub-paths
to represent the along-path changes in atmospheric condition with elevation. For
the INGV-Catania scenario we explore the effects of using different numbers of
sub-paths in comparison to the results from MODTRAN’s horizontal path results. |
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