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Summary of Proposal MTH0373

TitleA model to Segment volcanic superficial deposits in volcanoes of Mexico using Aster and TerraSAR images.
Investigator Davila, Norma - UNIVERSIDAD AUTONOMA DEL ESTADO DE MEXICO, Faculty of Geography, Laboratory of Remote Sensing and Geographic Information S
Team Member
researcher Lira, Jorge - Institute of Geophysics, National Autonomous University of Mexico., Natural resources
SummaryThe application of remote sensing for volcanic evaluation processes depends in great measure on the intensity of volcanic activity. Published studies are restricted to recent volcanic activity. In this proposal a segmentation model to volcanic superficial deposits using ASTER and TerraSAR-X data will be generated. A canonical expansion analysis and a ruggedness descriptor will be evaluated from Aster stereoscopic capability for the quantification of the spectral key response of volcanic spectral signatures that characterize the recent and ancient volcanic superficial deposits. On the other hand, the textural descriptor will be evaluated from TerraSAR-X data due to the fact that radar data shows a great textural content of the scene. Differential interferometry from multi-temporal Interferometric pairs Spotlight will be used, in order to assess deposits gradually eroded associated to both recent and ancient volcanic activity. Such analysis may therefore be useful for evaluation of volcanic hazard and risks assessment during a period of volcanic crisis.
Final ReportI. Results in terms of "Coherence Change Detection" (CCD)
I.I Grounds of CCD
The CCD is linked to Differential Interferometric Analysis (DIA) which is calculated the phase difference related to the rate of change between subjects or geodynamics events from two interferometric images by time series. This form, four maps of coherence change (CCD) were generated. Each map consist in a RGB composite, where each of the output bands that make up the composite image is resulting of a rate of change in magnitude and coherence, it means, the CCD can be analyzed like a decorrelation process between a complex pair (SLC) where the phase difference implies a rate of change manifested in a gain or loss in coherence and magnitude values.
Therefore, the result is an 8-bit image, where low values of coherence are pixels associated with change detection.
Thus, the RGB is generated in terms of the CCD and the difference of magnitude (DM) between interferometric pairs. Thus the composite image is defined as follows,
R: image result of CCD
G: image derived from the average magnitude between interferometric pairs
B: image generated from the difference in magnitude (DM) between interferometric pairs.
Therefore, 5 RGB images results in terms of CCD were generated.
It is important to mention, the combination of best pairs was based on minim baselines (tens of meters), an increase in the baseline produce a degradation in the values of coherence image.
I.II Identification of superficial volcanic deposits: piroclastic flows, lava flows, ash fall and undifferentiated deposits
The result in terms of CCD are showed in the figures 1 to 4. Each one of RGB images result linked to CCD is constituted in three segmentation units: the first segmentation unit named "total change areas" (TCA) is shown in dark green hues, while the second segmentation unit "medium change areas" (MCA) is shown in light green hues, and finally the third "no change areas" is shown in pink hues (NCA). It should be noted that the results presented below were verified based on fieldwork, which consisted identification of volcanic deposits units "in situ" using a GPS of high resolution and matched with the images result CCD.
Thus, in the four cases (figures 1 to 4) the TCA segmentation was associated to atmospheric noise, therefore, it was cataloged as total loss information; in geomorphologic terms the same area correspond to a debris avalanche sited 7000 years ago, and correspond to the last explosive period activity of the Nevado de Colima Volcano, located north of the Colima Volcano. It is important to mention that debris avalanche is cover for a dense vegetation characterized by coniferous forests and pine, so, the SAR signal can not penetrate through tree's foliage.
The second segmentation unit MCA correspond to two situations, first is linked debris flow emplacement on the proximal zone of ravines, constituting the source material of secondary events like lahars; second is linked to the effect of SAR incidence angle on volcanic slopes above 30°; this phenomenon is evident in Figures 2 and 3 where all right slope is illuminated by radar sensor (slange range) with a look direction: right, and orbit direction: ascending. The third segmentation unit NCA correspond to lava flow and pyroclastic flow historics near to the summit with a distance less than 6km, most of these volcanic deposits are associated to a specific activity period as years 2000, 2005 and 2008. In the case of far volcanic deposits correspond to alluvial fans and historic debris flows (lahars).
On the other hand, for this work, is the special interest the areas with pixels named "TCA" and "MCA" but keeping connectivity with pixels named "NCA". This have a direct relation with the recent volcanic activity of the Colima Volcano, in specific with its domic activity characterized by recurrent periods of growth and partial collapse of the dacitic dome, forming block and ash deposits and lava flows principally.
I.III Surface Geomorphology of recent volcanic deposits associated to CCD
On the other hand, the surface geomorphology of the volcanic deposit can be estimated based on CCD, that is to say, from the image composite (RGB in terms of CCD) it was possible to get the superficial topography of the volcanic deposits and geoforms of the proximal area of the principal ravines. Thus 3d simulations were generated from RGB image (R: image result of CCD, G: image derived from the average magnitude between interferometric pairs, B: image generated from the difference in magnitude (DM) between interferometric pairs). Different type of deposits were selected, in specific those proximal deposits (pyroclastic flows and block and ash) to the summit where the erosive process is highest, and therefore topographic changes could be expected. Therefore, Monte Grande, La Lumbre and El Zarco ravines presented the highest erosive activity, in the same way has a direct relation with the volcanic activity level. It is important to mention, these proximal ravines and deposits as debris flow and block and ash are linked to the segmentation units "MCA" and "NCA". Above results could not be estimated from original SAR images. In Figure 5 two 3D simulations are shown, with the object to compare results in terms of CCD and apparent change through time; pyroclastic and lava flow deposits were selected. Thus, based on the four interferometric pairs, morphologic changes through time could be estimated between deposits. For example, in figure 5 the lava flow 3D simulation showed a half plane superficial geomorphology, in field verification correspond to deposit up and there was not evidence of topographic changes through time; while the pyroclastic flow deposits showed a erosion process characterized by lateral block terrace that is evidence of a constant topographic change over ravines along multi-temporal interferometric pairs.
II. CONCLUSIONS
Two descriptors spectral and textural were used for spectral enhance and segmentation of superficial volcanic deposits (pyroclastic flows, lava flows, no differentiated units and lahar deposits as secondary events) linked to the recent effusive-explosive volcanic phase at Colima Volcano, México; also, based on radar interferometric process was utilized for identification of topographic changes using multi-temporal radar pairs. From spectral descriptor was possible the spatial evaluation and segmentation of lahar deposits using Terra/Aster and Spot 5 sensors for period 2004-2009, thus a Spectral Lahar Index was generated from third principal component, it showed a spectral difference between original bands 3 and 4 for both sensors, therefore, we can estimated a increment about the area distribution along period 2004-2009.
A interferometric process was applied based on TerraSAR data. Based on minimum base lines methodology, 4 interferometric pairs could be calculated. Thus, coherence, interferogram, differencial phase maps were calculated for differentiate each one volcanic deposits, except lahar deposits linked to recent volcanic activity with respect old deposits linked to old volcanic activity. Second, a differential process was applied for estimate and segment volcanic units named "Coherence Change Detection" (CCD) and find the topographic changes and superficial geomorphology of volcanic deposits along multi-temporal analysis (period 2008-2011). Thus, based on CCD, three segmentation units were obtained: "TCA", "MCA" and "NCA".
Based on results, we sustain that the application of remote sensing techniques and radar interferometry are useful tool for evaluations and monitoring of superficial volcanic deposits during a explosive period at Colima Volcano. In specific, Terrasar data allowed a right characterization of volcanic deposits in centimetric scale, and allowing the minimum topographic changes. However, the application of InSAR methodology in volcanic environmental can be difficult because the high slope deformations.
NOTE 1:
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NOTE 2:
It was impossible uploaded the publications in PDF format, the system sent the following message:
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So the reference of publications is as follows:
1.- Norma Dávila-Hernández, Jorge Lira, Lucia Capra-Pedol, Francesco Zucca. (2010). A normalized difference lahar index based on Terra/Aster and 1 Spot 5 images: an application at Colima Volcano, Mexico. Revista Mexicana de Ciencias Geológicas. VOL 28, No. 3. Link: http://rmcg.unam.mx/
2.- Norma Dávila-Hernández, 2011. Modelo de segmentación de depósitos volcánicos superficiales en el Volcán de Colima, México utilizando imágenes ópticas y de radar de alta resolución (TerraSAR-X). UNAM. Link: http://bcct.unam.mx/web/tesiunam.htm.
3.- Davila, N; Lira, J. 2010. Interferometric process using TerraSAR-X: A study At Colima Volcano, Mexico. Cities on Volcanoes 6th, Puerto de la Cruz, Tenerife, Spain.

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