Harold Garbeil

Automated volcanic eruption detection using MODIS

Abstract The moderate resolution imaging spectroradiometer (MODIS) flown on-board NASAs first earth observing system (EOS) platform, Terra, offers complete global data coverage every 1–2 days at spatial resolutions of 250, 500, and 1000 m. Its ability to detect emitted radiation in the short (4 μm)- and long (12 μm)-wave infrared regions of the electromagnetic spectrum, combined with the excellent geolocation of the image pixels (∼200 m), makes it an ideal source of data for automatically detecting and monitoring high-temperature volcanic thermal anomalies. This paper describes the underlying principles of, and results obtained from, just such a system. Our algorithm interrogates the MODIS Level 1B data stream for evidence of high-temperature volcanic features. Once a hotspot has been identified, its details (location, emitted spectral radiance, satellite observational parameters) are written to an ASCII text file and transferred via file transfer protocol (FTP) to the Hawaii Institute of Geophysics and Planetology (HIGP), where the results are posted on the Internet ( http://modis.higp.hawaii.edu ). The global distribution of volcanic hotspots can be examined visually at a variety of scales using this website, which also allows easy access to the quantitative data contained in the ASCII files themselves. We outline how the algorithm has proven robust as a hotspot detection tool for a wide range of eruptive styles at both permanently and sporadically active volcanoes including Soufriere Hills (Montserrat), Popocatepetl (Mexico), Bezymianny (Russia), and Merapi (Java), amongst others. We also present case studies of how the system has allowed the onset, development, and cessation of discrete eruptive events to be monitored at Nyamuragira (Congo), Piton de la Fournaise (Reunion Island), and Shiveluch (Russia).

Analysis of active volcanoes from the earth observing system

Abstract A study of volcanic activity and its effects on the atmosphere is one of 28 interdisciplinary investigations, for the Earth Observing System (EOS), due to be launched in 1997 and 1999. The volcanology investigation will include long- and short-term monitoring of selected volcanoes, the detection of precursory activity associated with unanticipated eruptions, and the detailed study of on-going eruptions. The data collected will allow us to address two aspects of volcanism: volcanic padforms and the atmospheric effects of eruptions. A variety of instruments on the two NASA EOS platforms, together with supplemental data from the Japanese and European platforms, will enable the study of local- to regional-scale thermal and deformational features of volcanoes, and the chemical and structural features of volcanic eruption plumes and aerosols. This investigation fits well within the overall goal of the EOS Project, which is to study the regional and global interrelationships between components of the Earth System, because it specifically investigates the links between volcanism, atmospheric chemistry and short-term (1–3 year) climate change.

Slopes of Western Galapagos volcanoes from airborne interferometric radar

The distribution of slopes on the six basaltic shield volcanoes in the Western Galapagos Islands is investigated using a digital elevation model derived from airborne interferometric radar (TOPSAR) data. These measurements have a spatial sampling of 10 m/pixel, a vertical accuracy of 3 to 5 m, and constitute the highest resolution, most complete, topographic data set available for the islands. Volcano heights are determined to range from 1,124 m (Sierra Negra) to 1,710 m (Wolf). Over extensive areas of each volcano, slopes exceed 25°, with the highest slopes being ∼37° on Wolf and ∼36° on Fernandina. We confirm that two morphologic subgroups exist: Cerro Azul, Fernandina, and Wolf, with deep calderas (depth between 40–60% of the subaerial height of the volcano) and steep (>20°) maximum slopes at elevations between ∼60 and 80% of the volcano height; and Alcedo, Darwin, and Sierra Negra, with shallow calderas (depth <25% of subaerial height) and slopes that remain <15° until ∼90% of the total height is reached. Our data show that steep slopes are not uniquely correlated with the occurrence of arcuate fissures at the summit, leaving the origin of the steep slopes unresolved.

Effects of viewing geometry on AVHRR observations of volcanic thermal anomalies

Abstract We investigate the influence of viewing geometry and dynamic range of the Advanced Very High Resolution Radiometer (AVHRR) sensor on detecting eruptions on poorly monitored volcanoes. Numerical models of sunwarmed flows and typical active features associated with Hawaiian eruptions (overturning lava lakes, surface flows of three different sizes, and lava tubes with skylights) show that new lava flows at ∼1000°C can be identified at all scan angles if the area of the activity exceeds ∼60 m 2 given a background temperature of 20°C. More difficult is the detection of small breakouts of lava flows or tube-fed flows when these features lie towards the edge of the swath; because of the dynamic range and gain setting of the sensor (Bands 3, 4, and 5 saturate at ∼49°C) it is possible that similar thermal signatures may be produced when inactive flows are heated by the Sun. The ability of the AVHRR to detect on-going activity in Hawaii in July 1991 is tested by comparing Landsat Thematic Mapper and nadir AVHRR scenes obtained within ∼3.5 hours of each other. For an active pahoehoe flow field with a well-developed tube system, this comparison shows that within the area of thermally alarmed AVHRR pixels

Deep impact craters in the Isidis and southwestern Utopia Planitia regions of Mars: High target material strength as a possible cause

] Using THEMIS, MOC and MOLA data, we havefound 51 craters in the diameter range 6–11.8 km withinsouthwestern Utopia Planitia and Isidis Planitia that aresignificantly deeper than typical fresh craters in the northernlowlands of Mars. The restricted geographic distribution ofthese craters, their simple morphology, and data fromimpact and explosion crater studies suggest that unusuallystrong target materials (as much as a factor of 2 greater thanaverage materials in the Martian lowlands) are the cause ofthe excessive crater depth. We propose that the greater targetmaterial strength acts to delay gravity-dominated collapse tolarger crater sizes. Furthermore, we suggest that a regional,olivine-rich mafic to untramafic rock unit identified by TESand THEMIS is a reasonable candidate for these strongmaterials. The unit is exposed on the southern edge of Isidisbasin and in crater ejecta within the basin, and forms layersthat dip toward the Isidis Basin center.

Ground-based Infrared Monitoring Provides New Tool for Remote Tracking of Volcanic Activity

Thermal monitoring of active volcanoes has long been the domain of satellite and airborne remote sensing (for reviews of current capabilities, see Harris et al. [2002]). However, ground-based thermal sensors offer considerable benefits in that (1) they can be located beneath cloud decks that prohibit aerial views; (2) they allow small thermal targets to be resolved; (3) they observe targets with a constant viewing geometry for long periods of time; and (4) they provide data at high sample rates (tens to hundreds of Hz). This latter capability is extremely attractive when tracking transient or rapidly evolving events, such as volcanic explosions. In addition, when used in conjunction with other geophysical data sets, thermal time series reveal clues as to the manner in which a volcanic system is erupting.

Geometry of Martian impact craters: First results from an interactive software package

[1] We have developed a new interactive computer program that facilitates the easy collection of geomorphic data for Martian impact craters, using the MOLA 128th degree digital elevation model of Mars. We describe the method for ensuring that accurate measurements of crater diameter, depth, rim height, rim volume, cavity volume, ejecta thickness, and ejecta volume are obtained. We compare our measurements of crater diameters and rim heights to results obtained by Garvin et al. [2000], who employed centerline MOLA profiles. Statistical regressions between the two methods give R 2 values of 0.930 for crater depths and 0.984 for crater diameters. The new interactive program facilitates the rapid compilation of large data sets to allow a comparison of crater populations in different settings. Preliminary results are presented for 354 craters on ridged plains materials in Hesperia and Sinai Plana to demonstrate the value of the program for regional comparisons and the analysis of degradational processes on Mars. INDEX TERMS: 5420 Planetology: Solid Surface Planets: Impact phenomena (includes cratering); 5494 Planetology: Solid Surface Planets: Instruments and techniques; KEYWORDS: geomorphology, impact craters, Mars

Digital topography of volcanoes from radar interferometry: an example from Mt Vesuvius, Italy

A new airborne radar technique can generate digital topographic data for volcanoes at a scale of 10 m spatial and 1–5 m vertical, with a swath width of ∼6.4 km. Called TOPSAR, the intrument is an interferometric radar flown on the NASA DC-8 aircraft. TOPSAR data permit the quantification of volcano slopes, volumes, and heights, and as such will be valuable for the analysis of lava flows, domes, and lahar channels. This instrument will be flown over several volcanoes in the near future, providing volcanologists with valuable data sets for the analysis of high-resolution topography. We briefly illustrate the potential use of TOPSAR data through examples from Mt Somma and Vesuvius, Italy.

TIRCIS: thermal infrared compact imaging spectrometer for small satellite applications

TIRCIS (Thermal Infra-Red Compact Imaging Spectrometer), uses a Fabry-Perot interferometer, an uncooled microbolometer array, and push-broom scanning to acquire hyperspectral image data. Radiometric calibration is provided by blackbody targets while spectral calibration is achieved using monochromatic light sources. The instrument has a mass of <10 kg and dimensions of 53 cm × 25 cm × 22 cm. The optical design yields a 120 m ground sample size given an orbit of 500 km. Over the wavelength interval of 7.5 to 14 microns up to 90 spectral samples are possible. Our performance model indicates signal-to-noise ratios of 400-800:1.

Topographic change on volcanoes from SRTM and other interferometric radars

Data from the Shuttle Radar Topographic Mission (SRTM) will permit extensive analysis of volcanoes and volcanic processes in many parts of the world that are infrequently studied by field volcanologists. In preparation for the release of the SRTM data, we have been conducting several studies of volcanoes using digital elevation data collected either from airborne interferometric radars (the TOPSAR and Star-3i systems) or from repeat-pass radar interferometry from the ERS-2 spacecraft. We report here on our results from these preparatory studies in the Philippines, Java and the Galapagos Islands, and suggest how SRTM observations will enhance future work in these areas.