A comparison of field- and satellite-derived thermal flux at Piton de la Fournaise: implications for the calculation of lava discharge rate |
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Authors: | D Coppola M R James T Staudacher C Cigolini |
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Institution: | 1. Dipartimento di Scienze Mineralogiche e Petrologiche, Università di Torino, Via Valperga Caluso 35, Torino, Italy 2. Department of Environmental Science, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK 3. Observatoire Volcanologique du Piton de la Fournaise, 14 RN3—Km 27, 97418 La Plaine des Cafres, La Réunion, France
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Abstract: | We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial
resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May–July 2003 eruption
at Piton de la Fournaise (La Réunion). Multiple oblique ground-based thermal images were merged to provide full coverage of
the flow-field. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance
emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption
reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements
represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless,
extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from
94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat
flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface
that were 6–24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge
Rate (TADR) ranged between 1.5 × 108 J m−3 and 3.5 × 108 J m−3. This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained
from GPS surveys (Coppola et al. 2005). Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements,
particularly in terms of calculating discharge rate trends. |
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