Methods for analyzing surface texture effects of volcanoes with Plinian and subplinian eruptions types: Cases of study Lascar (23 S) and Chaiten (42

📝 Abstract

This paper presents a new methodology that provides the analysis of surface texture changes in areas adjacent to the volcano and its impact product of volcanic activity. To do this, algorithms from digital image processing such as the co-occurrence matrix and the wavelet transform are used. These methods are working on images taken by the Landsat satellite platform sensor 5 TM and Landsat 7 ETM + sensor, and implemented with the purpose of evaluating superficial changes that can warn of surface movements of the volcano. The results were evaluated by similarity metrics for grayscale images, and validated in two different scenarios that have the same type of eruption, but differ, essentially, in climate and vegetation. Finally, the proposed algorithm is presented, setting the parameters and constraints for implementation and use.

💡 Analysis

This paper presents a new methodology that provides the analysis of surface texture changes in areas adjacent to the volcano and its impact product of volcanic activity. To do this, algorithms from digital image processing such as the co-occurrence matrix and the wavelet transform are used. These methods are working on images taken by the Landsat satellite platform sensor 5 TM and Landsat 7 ETM + sensor, and implemented with the purpose of evaluating superficial changes that can warn of surface movements of the volcano. The results were evaluated by similarity metrics for grayscale images, and validated in two different scenarios that have the same type of eruption, but differ, essentially, in climate and vegetation. Finally, the proposed algorithm is presented, setting the parameters and constraints for implementation and use.

📄 Content

Methods for analyzing surface texture effects of volcanoes with Plinian and subplinian eruptions types: Cases of study Lascar (23° 22’ S) and Chaiten (42 ° 50’ S), Chile.

Abstract: This paper presents a new methodology that provides the analysis of surface texture changes in areas adjacent to the volcano and its impact product of volcanic activity. To do this, algorithms from digital image processing such as the co-occurrence matrix and the wavelet transform are used. These methods are working on images taken by the Landsat satellite platform sensor 5 TM and Landsat 7 ETM + sensor, and implemented with the purpose of evaluating superficial changes that can warn of surface movements of the volcano. The results were evaluated by similarity metrics for grayscale images, and validated in two different scenarios that have the same type of eruption, but differ, essentially, in climate and vegetation. Finally, the proposed algorithm is presented, setting the parameters and constraints for implementation and use.

Keywords: subplinian eruption, co-occurrence matrix, wavelet transform, similarity metrics.

L. Fernández • G. Álvarez Universidad de Antofagasta, Ave. Angamos 601, Antofagasta, Chile e-mail: luis.fernandez@uantof.cl

G. Álvarez e-mail: gabriel.alvarez@uantof.cl

R. Salinas Universidad de Santiago de Chile, Ave. Bernardo O’Higgins 3363, Santiago, Chile e-mail: renato.salinas@usach.cl

1 Introduction In the process of a volcano eruption in general, it is possible to appreciate some spatial deformation of the volcano, also, depending on the type of eruption it is possible to measure the effects of the eruption on the surface (Fernandez L, et al. 2012). Studies have been conducted to evidence of multi deformations pre- eruptive disorders, post-eruptive and assess the impact of the eruption (Ortiz 1996). The methods can be grouped into two: On one side, the direct methods, which are inclinometry, leveling, check, distance using the impedance, etc. On the other side, we have the distance methods, by which measurements can be performed through a remote sensor. In this group, there is a huge range of devices, including laser ranging, photogrammetry, radiometry, GPS, etc.

It has been documented in the literature about surface deformations using satellite images (Whelley et al 2010; Pavez et al., 2006). As for images captured by passive sensors, Landsat have been used primarily for the study of thermal anomalies (Glaze et al 1989a, 1989b; Wooster 2001), morphologic classification (Bailey et al., 2007), evolution of the volcanic dome (Francis and Rothery 1987; Oppenheimer et al., 1993), among others.

Because of the deformation of the surface of the Earth, one can hope detecting these changes with a remote sensor; however, remote sensors depending on your bandwidth and radiometric resolution are not able to detect these changes on the surface or, in other words, the change of the terrain texture (Haralick et al. 1973). Specifically, in the range of visible wavelengths some shape changes do not alter the colour field, in this case the changes go unnoticed, on the other hand, in the range of radar wavelength it is impossible to detect changes in form altering the earth’s surface that are parallel to the line of flight of the satellite platform (azimuthal direction).

The texture theme discussed in the literature distinguishes four methods, mainly: statistical, geometric or structural, based on models and based on transforms or signal processing (Tuceryan and Jain 1998; Materka and Strzelecki 1998; Epifanio 2002; Sucar and Gómez 2003; Fernandez A, 2007; Iglesias 2009). Because of these methodologies, a number of products obtained need to be validated, it is necessary to establish measures that allow a comparison sizing the existence of changes. In the case of grayscale representations, it is common to use similarity metrics (Svedlow et al. 1976), correspondence regions (Marcello et al. 2007) or disparity maps (Colodro et al. 2012).

2 Hypothesis Volcanic eruptions have shaped the surface of the Earth from its early origin. Movement of magma through the volcanic edifice characterizes these processes. This process can occur with deformation of the surrounding surface or it may be overlooked from the geomorphological point of view, however, the impact on the surface of the Earth of volcanic ash, Pyroclastic flows and morphological deformations, depending on the scale, may become evident and measurable by sensors deployed in satellite platforms in almost all ranges of the electromagnetic spectrum. Algorithms such as co-occurrence matrix, wavelet transform, Sobel operator and growth regions have been successful to classify satellite images for their texture. Therefore, if there are changes in the texture of the surface of the Earth in a volcanic eruption process, they should be classifiable and measurable to a scale consistent with the resolution of the

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