Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 1 Athanassios Ganas &*, Evangelos Lagios †, G. Petropoulos ‡▼, Basil Psiloglou # & Geodynamics Institute, National Observatory of Athens, P.O. Box 20048, Athens , Greece. † Space Applications Unit in Geosciences, Dept. of Geophysics & Geothermics, University of Athens, Panepistimiopolis – Ilissia, Athens , Greece. ‡ Department of Geography, King’s College London, Strand Campus, WC2R 2LS, London, UK. # Institute of Environmental Research and Sustainable Development, National Observatory of Athens, I. Metaxa & Vas. Pavlou Str., Athens, Greece. ▼Now at: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK. *corresponding author: Thermal Imaging of Nissyros Volcano (Aegean Sea) using ASTER data: Estimation of radiative Heat Flux.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 2 Aims and Objectives the present study investigates the use of information from multispectral infrared sensors orbiting from space, like ASTER, as a very promising method for the estimation of geophysical variables that are related to the monitoring of hydrothermal volcanic activity. Radiative heat flux is of key interest as this consists often an important indicator of the complex processes underlying the event of a possible eruptive condition. The present study comprises the first comprehensive attempt to invert for this important feature using ASTER satellite data in Nissyros volcano, one of the many hydrothermally active volcanoes in the Mediterranean. Thermal Imaging of Nissyros Volcano (Aegean Sea) using ASTER data: Estimation of radiative Heat Flux.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 3 Setting of Nissyros volcano in the south-east Aegean Sea. Inset box shows the location of the Quaternary volcanoes of the Aegean Arc and ages of volcanism. Image from the GEOWARN web site:

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 4 Geophysical instrumentation on Nissyros volcano in the south-east Aegean Sea.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 5 Geological Map of Nissyros.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 6 Air-photograph of Nissyros volcano in the south-east Aegean Sea. View to the West-southwest.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 7 Field photograph of the Nissyros caldera (20 May 2002). View to the South. The crater areas are shown together with normal faults that dip towards the interior of the caldera.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 8 EO Data Four (4) cloud-free night-time ASTER images acquired over the area of interest on: 7 April 2001, 13 June 2002, 26 October 2002 and 23 July 2005.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 9 ASTER Data Processing a height-independent, corrected temperature (θ) was calculated for each pixel in order to remove surface temperature variations caused by cooler air temperatures at higher altitudes where T is the ASTER derived surface Temperature (product AST08), h is surface altitude and α is the adiabatic gradient (0.006  C m -1 ). Heat Flux (Qrel) is a function of surface emissivity, temperature and water vapour. e is vapour pressure (mbar) and Δθ is the difference in  C between maximum θ within the thermal anomaly (crater) and minimum θ from all pixels near to the anomaly (Gaonac’h et al., 1994). Spectral emissivity was determined from AST05 product. Water vapour from the Heraklion Airport midnight radiosonde launches.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 10 Temperature map of the Nissyros volcano. Increasing brightness indicates warmer surface temperatures. The map shows theta values for 13 June 2002 (left) and 26 October 2002 (right).

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 11 Temperature map of the crater region inside the Nissyros caldera on 13 June 2002 (left) and 26 October 2002 (right). Thin white lines are elevation contours (interval 20 m). Red lines on the left image indicate normal faults Red polygons on the right image indicate extent of thermal anomalies used to calculate total flux in the Nissyros caldera.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 12 Diagram of radiative heat flux (Qrel) measurement from ASTER data for Nissyros volcano over the period Date format on axis X is DD/MM/YY

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 13 Diagrams showing non-linear vs linear dependence of radiative heat flux (Qrel) on vapour pressure (a) and spectral emissivity (b). Qrel estimates refer to the October 2002 ASTER image.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 14 UTM grid showing the location of hot pixels for all four ASTER images. All hot spots are grouped in three areas except for the outlier in the Polyvotis region ( ). Double line with dots indicates location of fissure. Pixel size is 100 m

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 15 Conclusions a) Image analysis of ASTER night-time scenes of Nissyros volcano suggests an almost steady state of heat flux over the period b) An average value of 36 MW (± 6 MW) of radiative heat flux is obtained inside the caldera at the time of ASTER overpass. This value is the “background” reference heat-flux for this volcano. c) Heat-flux estimates are highly sensitive to water vapour pressure, so radiosonde data from launches closer to this volcano would provide more accurate results.

Naples, November 2008 Second workshop on Use of Remote Sensing Techniques for Monitoring Volcanoes and Seismogenic Areas (USEReST 2008). 16 Nissyros EO Publications GANAS, A. and LAGIOS, E., 2003, LANDSAT7 thermal imaging of the Nissyros Volcano. International Journal of Remote Sensing, 24, GANAS, A., VASSILOPOULOU, S., LAGIOS, E., and SAKKAS, V., 2003, Thermal Imaging of Nissyros Volcano (Aegean Sea) using ASTER data. Bulletin of the Geological Society of Greece, 35, LAGIOS, E, VASSILOPOULOU, S, SAKKAS, V, DIETRICH, V, DAMIATA, BN and GANAS, A, 2007, Testing satellite and ground thermal imaging of low-temperature fumarolic fields: The dormant Nissyros Volcano (Greece). ISPRS Journal of Photogrammetry and Remote Sensing, 62 (6), SACHPAZI, M., KONTOES, CH, VOULGARIS, N, LAIGLE, M, VOUGIOUKALAKIS, G, SYKIOTI, O, STAVRAKAKIS, G, BASKOUTAS, J, KALOGERAS, J, and LEPINE, JCL, 2002, Seismological and SAR signature of unrest at Nissyros caldera, Greece, Journal of Volcanology and Geothermal Research, 116 (1- 2), SYKIOTI, O., KONTOES, CC., ELIAS, P., BRIOLE, P., SACHPAZI, M., PARADISSIS, D., and KOTSIS, I., 2003, Ground deformation at Nisyros volcano (Greece) detected by ERS-2 SAR differential interferometry, International Journal of Remote Sensing, 24(1),