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| In the years between 1980 and 1991, a large area surrounding Mount St Helens was known to be deforming, resulting in a total of 1-3 cm of uplift. This uplift was measured by trilateration surveys conducted in 1982 and 1991 and was interpreted to be the result of post-eruptive recharge of a deep magma chamber beneath Helens. Interestingly, through the time of the eruption, no further deformation was measured through a synthesis of trilateration data, collected on a broad scale, and campaign GPS surveys conducted in 2000 and 2003, at 17 stations within 5km of the crater. However, if the total displacements from 2000-2003 were small, less than 2 cm, they may have been below the survey’s level of detection. Additional measurements made by a continuous GPS station located at the Johnston Ridge Observatory, approximately 9km away from the crater, did not indicate any surface deformation. | In the years between 1980 and 1991, a large area surrounding Mount St Helens was known to be deforming, resulting in a total of 1-3 cm of uplift. This uplift was measured by trilateration surveys conducted in 1982 and 1991 and was interpreted to be the result of post-eruptive recharge of a deep magma chamber beneath Helens. Interestingly, through the time of the eruption, no further deformation was measured through a synthesis of trilateration data, collected on a broad scale, and campaign GPS surveys conducted in 2000 and 2003, at 17 stations within 5km of the crater. However, if the total displacements from 2000-2003 were small, less than 2 cm, they may have been below the survey’s level of detection. Additional measurements made by a continuous GPS station located at the Johnston Ridge Observatory, approximately 9km away from the crater, did not indicate any surface deformation. | ||
| + | {{:mark:poland_and_lu.jpg}} | ||
| Because of the wide spatial and temporal spacing, and to a lesser extent, the levels of noise, in data collected by trilateration and GPS, no conclusions could be made about any potential surface deformation that may have occurred locally on the edifice or within the crater of Helens. The ability to produce spatially continuous maps of surface displacements gives InSAR the ability to resolve the question of whether localized deformation may have occurred at Mt St Helens prior to its 2004 eruption. A study conducted by Poland and Lu in 2008 attempted to image both pre and post eruptive deformation at Mount St Helens using interferogram stacking. Because of decorrelation caused by the presence of snow and dense vegetation, even stacks of interferograms were unable to obtain signal within the crater or on the edifice prior to the eruption (Fig ##). While the results prior to the 2004 eruption were inconclusive, post eruptive results successfully imaged subsidence around and on parts of the edifice. | Because of the wide spatial and temporal spacing, and to a lesser extent, the levels of noise, in data collected by trilateration and GPS, no conclusions could be made about any potential surface deformation that may have occurred locally on the edifice or within the crater of Helens. The ability to produce spatially continuous maps of surface displacements gives InSAR the ability to resolve the question of whether localized deformation may have occurred at Mt St Helens prior to its 2004 eruption. A study conducted by Poland and Lu in 2008 attempted to image both pre and post eruptive deformation at Mount St Helens using interferogram stacking. Because of decorrelation caused by the presence of snow and dense vegetation, even stacks of interferograms were unable to obtain signal within the crater or on the edifice prior to the eruption (Fig ##). While the results prior to the 2004 eruption were inconclusive, post eruptive results successfully imaged subsidence around and on parts of the edifice. | ||
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| In this study, the Stanford Method for Persistent Scatterers developed by Hooper et al. (2012) was applied to a set of eight SAR scenes collected by the ERS-2 satellite covering Mount St Helens over the pre-eruptive period, from 1996 to 2002 (Figs ##, ##). Many SAR scenes from track 156, frame 2673 were available, but only those from the summer and fall months were chosen in order to minimize the effects of snow. During processing, the number of scenes was further reduced to eight after interferogram pairs having poor perpendicular baselines and high decorrelation were eliminated. Additional SAR datasets from different track –frame combinations exists over Mount St Helens, but are more limited in the time they span, and their number of scenes. | In this study, the Stanford Method for Persistent Scatterers developed by Hooper et al. (2012) was applied to a set of eight SAR scenes collected by the ERS-2 satellite covering Mount St Helens over the pre-eruptive period, from 1996 to 2002 (Figs ##, ##). Many SAR scenes from track 156, frame 2673 were available, but only those from the summer and fall months were chosen in order to minimize the effects of snow. During processing, the number of scenes was further reduced to eight after interferogram pairs having poor perpendicular baselines and high decorrelation were eliminated. Additional SAR datasets from different track –frame combinations exists over Mount St Helens, but are more limited in the time they span, and their number of scenes. | ||
| Results | Results | ||
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| + | {{:mark:big_map.jpg}} {{:mark:table.jpg}} | ||
| StaMPS processing was run successfully on the pre-eruptive ERS-2 data, yielding a decent density of stable pixels both on the edifice and within the crater. Refined interferograms were created alongside maps of average velocity over the timespan of 1996-2002. An example interferogram and average velocity map overlain on Google Earth imagery are shown below (Figs ##, ##). | StaMPS processing was run successfully on the pre-eruptive ERS-2 data, yielding a decent density of stable pixels both on the edifice and within the crater. Refined interferograms were created alongside maps of average velocity over the timespan of 1996-2002. An example interferogram and average velocity map overlain on Google Earth imagery are shown below (Figs ##, ##). | ||
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| + | {{:mark:ex_int.jpg}} | ||
| + | {{:mark:stamps.jpg}} | ||
| **Discussion and Conclusions of StaMPS Processing** | **Discussion and Conclusions of StaMPS Processing** | ||
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| StaMPS processing of SAR data over Mount St Helens identifies pixels with low phase noise on the edifice and within the crater. This indicates that there is promise for Persistent Scatterers processing techniques like StaMPS to overcome decorrelation due to snow and trees and potentially image pre-2004 eruptive deformation. However, because of the possibility that StaMPS results are heavily influenced by atmospheric changes which are difficult to remove using the phase - elevation correlation alone, more work must be done before real signal can be differentiated from artifacts of the atmosphere removal process. It is this fact which motivates the second part of this study: an investigation of the effects of atmosphere on StaMPS processing at Mount St Helens. | StaMPS processing of SAR data over Mount St Helens identifies pixels with low phase noise on the edifice and within the crater. This indicates that there is promise for Persistent Scatterers processing techniques like StaMPS to overcome decorrelation due to snow and trees and potentially image pre-2004 eruptive deformation. However, because of the possibility that StaMPS results are heavily influenced by atmospheric changes which are difficult to remove using the phase - elevation correlation alone, more work must be done before real signal can be differentiated from artifacts of the atmosphere removal process. It is this fact which motivates the second part of this study: an investigation of the effects of atmosphere on StaMPS processing at Mount St Helens. | ||
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| + | **Section 2** | ||
| **Investigation of the Effects of Atmospheric Variability on StaMPS InSAR at Mount St Helens** | **Investigation of the Effects of Atmospheric Variability on StaMPS InSAR at Mount St Helens** | ||
