Heat Flux Monitoring Using Satellite Based Imagery at Karapiti (Craters of the Moon) Fumarole Area, Taupo, New Zealand

Authors: Md. Bodruddoza MIA, Chris J. BROMLEY, Yasuhiro FUJIMITSU
Keywords: radiative heat flux,geothermal heat flux, Landsat TIR data, Karapiti fumaroles, New Zealand
Conference: Stanford Geothermal Workshop Session: Geophysics
Year: 2012 Language: English
Geo Location:
Abstract: LANDSAT thermal infrared data (30 m pixel resolution), supported by spot ground measurements, were used in this study to investigate changes between 1990 and 2011 in the radiative heat flux (RHF) from the 0.5 km2 Karapiti fumarole area, at Wairakei Geothermal Field, Taupo, New Zealand. An objective was to calculate the net RHF of the geothermal area in order to reduce the effect of solar heating in these satellite infrared images. The result showed that the RHF decreased between1990 and 2011 by a total of about 29 MW. The net RHF (geothermal radiative heat flux) decreased by about 13 MW from 2000 to 2011. Another method of estimating net RHF, by subtracting the total incident direct solar heat load, also showed a decreasing trend, from about 96 to 67 MW during the study period. A vegetation index from the LANDSAT-TM/ETM+ VNIR bands (NDVI) was used to undertake a land-cover study. Results implied that the area of healthy vegetation at Karapiti progressively increased during this period. This supports the evidence for a decrease in geothermal heat losses, because the health of thermally-stressed vegetation is inversely related to shallow ground temperature. Images of apparent land-surface temperature (LST) were statistically sampled using a random spatial distribution of 100 points. Though the results show large variations with time, overall, there is a decreasing trend. As expected, there is a strong correlation between LST and RHF from all analyzed images. Spot ground estimations of heat flux using a calorimeter, when repeated, also showed, on average, a decreasing trend of heat flux between 2000 to 2009, although several sites showed stable heat flux. Further supporting evidence came from repeated ground-based temperature-depth profiles, which showed that the near-surface boiling point depth lowered in level at most sites between 2000 and 2011, although several sites located in actively-steaming bare-ground (~98°C at ~0.1m depth) remained relatively stable. In conclusion, satellite imagery and supporting ground-based evidence suggest a pattern of gradual decline (despite some time and spatial variation) in overall heat flux over the past decade from the Karapiti fumarole area.
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