Minoru Urai

Size and volume evaluation of the caldera collapse on Piton de la Fournaise volcano during the April 2007 eruption using ASTER stereo imagery

[1] The scale of summit collapse during the April 2007 eruption of Piton de la Fournaise volcano, Reunion Island, western Indian Ocean, was evaluated using before-and-after differential digital elevation models (DEMs) derived from nadir and backward-looking images from the Advanced Spaceborne Emission and Reflection radiometer (ASTER) instrument. The dimensions of horizontal length and width, volume and depth of the depression were estimated as 1,100 Â 800 m, 9.6 Â 10 7 m 3 and 320 m, respectively. These estimates show excellent agreement with field survey data. A ring shaped thermal anomaly (diameter of about 500 m) was found at Dolomieu Crater during or just after the collapse on nighttime ASTER SWIR image. It may correspond to the high temperature areas associated with the cross section of a hydrothermal zone at a constant altitude inside the crater. Our analysis of ASTER orbital data documents topographic and related thermal changes as a result of the 2007 eruption and demonstrates the power of ASTER as a volcanological tool. Citation: Urai, M., N. Geshi, and T. Staudacher (2007), Size and volume evaluation of the caldera collapse on Piton de la Fournaise volcano during the April 2007 eruption using ASTER stereo imagery, Geophys.

Heat discharge estimation using satellite remote sensing data on the Iwodake volcano in Satsuma-Iwojima, Japan

A series of heat discharges from the Iwodake volcano was estimated using nighttime Landsat TM data. The data includes heat discharge only from steaming ground and excludes fumarole, hot spring activities and others. The heat discharge was estimated at 40–80 MW from 1989 to 1993 using temperature distributions derived from Landsat TM band 6, and started to increase since 1995. From the error analysis, the true heat discharge will be in the range from −60% to +20% of the calculated discharge of this method. Two hot spots in the northeast to southwest direction correspond to the high temperature fumaroles seen in the temperature distributions derived from band 7. A new hot spot corresponds to a new degassing vent has been observed on the southern end of the summit crater since January 1992, and expanded to the same size as the other two hot spots since December 1993.

Identifying Surface Materials on an Active Volcano by Deriving Dielectric Permittivity From Polarimetric SAR Data

Dielectric permittivity εr measured on the Earths surface is an effective property for characterizing surface materials in terms of rock type and water content, particularly in highly changeable environments such as active volcanoes. We propose a technique termed dielectric permittivity from polarimetric synthetic aperture radar (dPSAR) to quantify εr using a single scene of polarimetric SAR data, based on the small perturbation model of backscattering (SPMB). For an optimal solution, the Nelder-Mead simplex method was combined with SPMB. The application of dPSAR to a scene of ALOS PALSAR data from the vicinity of Mt. Merapi, Indonesia, correctly identified the relative value ranges of εr for pyroclastic flow and tephra deposits accompanying large eruptions that occurred on November 5, 2010; their means were 2.55 and 3.07, respectively. Pore water within porous ashes is a plausible factor for increases in the εr of the tephra.

ASTER Applications in Volcanology

Satellite remote sensing is a powerful tool for volcano monitoring. The Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER), which was launched on the Terra platform in 1999, is a high spatial resolution imaging spectroradiometer in the visible to near infrared, shortwave infrared (SWIR), and thermal infrared regions (Yamaguchi et al. 1998). ASTER data are useful to study volcanoes through the following activities: (1) topographic and geologic analysis, (2) mapping volcanic products, (3) eruption plume analysis, (4) discolored seawater and crater lake monitoring, (5) generating digital elevation models, (6) surface temperature mapping, and (7) sulfur dioxide emission analysis (Pieri et al. 1995). The unique features of the ASTER instrument such as along-track stereo imaging and multispectral thermal infrared radiometry allow deriving additional information about volcanoes. In this chapter, we discuss some of the capabilities of ASTER for volcanological observations and analyses, and summarize some case studies.

Analysis of Coastal Sedimentation Impact to Jakarta Giant Sea Wall Using PSI ALOS PALSAR

The Jakarta province proposed the Jakarta Giant Sea Wall as the waterfront city for the new urban settlement zone and the deep seaport for the new economic zone along the coastal areas at northern Jakarta. This letter investigated land deformation at 11 watersheds of the West Java Mega Urban Region using the persistent scatterer interferometry technique of the Advanced Land Observing Satellite phased-array-type L-band synthetic aperture radar data. The result shows that land deformation at the study area, particularly the Bandung city area gives a significant impact to sedimentation velocity along the eastern Jakarta strait, particularly the deep seaport for 43 years later. This letter recommends to evaluate land conservation at upland watersheds and the well management of artificial canals to reduce the impact of sedimentation at the Jakarta strait, particularly the new depth seaport.

Observing 2006–2010 ground deformations of Merapi volcano (Indonesia) using ALOS/PALSAR and ASTER TIR data

Understanding precursory signal leading to a large and explosive eruption, such as Merapi eruption in 2010, is the key to a successful hazard assessment in the future. Towards resolution of this problem, time series of Differential Interferometric SAR (D-InSAR) of ALOS/PALSAR data together with thermal radiance at summit area were analyzed to characterize magmatic process. The D-InSAR could detect deformation changes in between two eruption episodes of Merapi in 2006 and 2010. The maximum uplifting rate ∼0.7 mm/day is observed twice: two years and one month before eruption in October 26, 2011. The first uplift is related to magma ascent and the later is precursory to an imminent eruption. Thermal radiance of ASTER data not only served as indicator on the arrival of fresh magma near the surface, but also to confirm whether or not the deformation signal is related to the imminent eruption.

Analysis of land deformation velocity using PSI ALOS PALSAR: Impact of coastal sedimentation to future Jakarta giant sea wall and waterfront city

In this research, we held study on land deformation at eleven watersheds that influence the sedimentation around Jakarta strait using PSI technique of ALOS PALSAR images. The result shows that land deformation at Jawa Barat province, especially Bandung city area gives significant impact to sedimentation velocity along eastern Jakarta strait, especially deep seaport as new economic zone of Jakarta Giant Sea Wall plan. We recommend to evaluate land conservation at Jawa Barat province and well management of artificial canals at eastern Jakarta strait to reduce the sedimentation.

East-Asia land surface emissivity maps generated from Terra/ASTER data archives

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a high-spatial-resolution multispectral imager on the Terra satellite launched in December 1999. The ASTER thermal infrared (TIR) subsystem has five spectral bands with a spatial resolution of 90 m in the TIR spectral region, which are used for generation of the standard products of surface temperature and surface spectral emissivity. High-resolution surface emissivity at five spectral bands is unique, and is particularly useful for geological mapping. However, the emissivity product is not always easy to use, because (1) its image size is about 60 km square which is not large enough for regional-scale studies, (2) its imaged area is not fixed to the world reference system (WRS) due to a flexible pointing system, and (3) standard atmospheric correction often fails under humid conditions. Thus, in order to improve the usability of the ASTER emissivity product, we are generating land surface emissivity maps in a regional scale by applying improved retrieval algorithms and stack/mosaic processing to an ASTER orthogonal projection dataset which have been produced from the ASTER data archives by the Advanced Industrial Science and Technology (AIST), Japan. In the present paper, we introduce East-Asia land surface emissivity maps as the first result of this project. A comparison study with MODIS monthly emissivity products (MOD11C3) indicates that the generated maps give more reasonable emissivity spectra with higher spatial resolution than the MODIS emissivity products, though the maps have missing pixels in high latitude areas and humid areas.

Observing lava dome roughness on synthetic aperture radar (SAR) data: Case study at Mt. Sinabung and Merapi — Indonesia

Detecting ground surface changes at active volcanoes is crucial for better hazard mitigation. Ground based measurements are commonly used to detect surface changes especially on the flanks near to the summit. However, the selection of observation points is limited by field conditions such as rough terrain and topographical barrier. The few number of observation points may lead to miss-interpretation when the displacements related to magma ascent occurred beneath unobserved flanks. This classical problem is common for dormant volcanoes. Overcoming the problem, we used the Synthetic Aperture Radar (SAR) data to observe surface roughness changes at the summit of active volcanoes. This paper discussed the potential capability of the SAR backscattering intensity to observe ground surface changes in view point of surface roughness around the summit. We presented two study cases at Mt. Sinabung in North Sumatra and Mt. Merapi in Central Java - Indonesia. Mt. Merapi was selected for comparison following published references. Mt. Sinabung is currently active since the first phreatic eruption has been occurred in August 2010. Time series of lava dome roughness on SAR (drSAR) method were used to detect ground surface changes prior to the eruption. Based on this method, the ground surface at the summit of Mt. Sinabung changed from 5121 to 6584 m2. The temporal pattern slightly agreed to the ground surface changes at summit of Mt. Merapi prior to the 2010 eruptions. Observing ground surface changes related to surface roughness at the summit might be used as new tools for observing volcanic activity.

Volcano observations with aster and ASTER Image Database for Volcanoes

ASTER was launched on December 1999 and has observed many volcanic eruptions. Through these observations, ASTERs ability to monitor volcanic activities, such as thermal anomalies, topographic changes, volcanic gases, among others, has been validated. A web-based ASTER Image Database for Volcanoes that contains all ASTER images of 964 volcanoes is developed and released. All ASTER images that include a part of the 20 km by 20 km area centered on the geographic location of volcano are stored in the database. Usually newly acquired image is added to the database within a week. It helps to promote the use of ASTER images to volcanologists.