Radiance Trends and Magma Flux at Hot Volcanoes

Donegan, Stephen James (2005). Radiance Trends and Magma Flux at Hot Volcanoes. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f64f

Abstract

In this thesis I use a range of remote sensing data, ranging from simple ground-based radiometers, through thermal imaging cameras to the latest space-based high-resolution multispectral instruments for the observation of active volcanic phenomena. I consider small scale degassing events within the Pu'u'O'o crater of Kilauea volcano, and provide a critique of the often used "dual-band" method for obtaining sub-pixel thermal information. I go on to use improvements of this method to provide the basis of a comparison of the existing and well understood Landsat7 ETM+ with the new EO-1 ALI with respect to volcanic observations.

This thesis falls into two main sections. In the first section I use thermal data from an array of simple radiometers operated by the University of Hawaii and the USGS Hawaii Volcano Observatory, coupled with basic RSAM data to identify degassing events at a small vent within the Pu'u'O'o crater. I relate these events to the semi-diurnal and fortnightly lunisolar tides. I show that there is a very weak relationship between these events and the semi-diurnal tide, but conversely a stronger relationship exists between the degassing events and the fortnightly tide. I show that these observations are consistent with previous observations of the fluctuating levels of the 1919 Halema'uma'u lava lake on Kilauea, and may be used as part of a synergistic approach to aid understanding of the complex Pu'u'O'o plumbing system. I go on to use thermal diffusion modelling to determine the mass of ejecta associated with certain degassing events that appear to possess well defined cooling curves in the radiometer data. By using software modelling iteratively applied to thermal diffusion equations, I show that the time taken for the temperature record from a spattering event to return to the ambient temperature is a function of the mean size of spatter blebs associated with the event. I use both laboratory tests and actual data recorded from a two month study period in 2001. This section of the thesis highlights that it is possible to obtain high-value information of active volcanic events without the cost of satellite data.

The second section of this thesis deals mainly with analysis of the dual-band method for extracting sub-pixel thermal information from multispectral satellite data. I use high-resolution ground based thermal imagery to generate simulated EO-1 ALI pixels, which can be adjusted to simulate a variety of likely volcanic scenarios. The second section of this thesis deals mainly with analysis of the dual-band method for extracting sub-pixel thermal information from multispectral satellite data. I use high-resolution ground based thermal imagery to generate simulated E0-1 ALI pixels, which can be adjusted to simulate a variety of likely volcanic scenarios. I apply the dual band method to this simulated imagery and analyse the response in detail. I show that it is preferable to use relative estimates of sub-pixel thermal structure rather than the exact estimates provided of the resulting factors. I also show how the results returned by the dual-band method may change ifthe lava flow is angled with respect to the instrument, due to the combined effects of ·the slope angle down which the flow is moving and the instrument look angle.

I finally assess the response of the recent E0-1 AdvanGed Land Imager to the remote sensing oflava flows in comparison to the established Landsat7 ETM+. I use the dual-band technique as the basis of this comparison, despite the flaws previously discussed, because it proviµes a valid means of comparison that remains valid if used in a relative fashion. I show that the E0-1 ALI is of great use for the remote sensing of lava flows due to the provision of extra channels within the SWIR, not present on the ETM+. These extra channels provide better solutions to the dual-band method as they are less susceptible to saturation and better placed within the spectrum for detection of volcanic products, than those of the ETM+.

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