Here, in this article I follow on from Part 1 that focused on webcams and thermal cameras and I report on some of the capabilities spaceborne sensors, which can detect thermal signals, map out volcanic flows and detect/measure volcanic plumes and clouds in real-time. The data from this equipment can then be used for systematically detecting changes in volcanic activity.
Satellite-based remote sensing
Satellite remote sensing has been used for monitoring and analyzing a volcanoes thermal activity, one can even go back to Oppenheimer (1998) who provides an excellent overview. Sensors available today can measure from the ultraviolet (nanometers) to the microwave (cm to m). Here, Ii focus on the use of ultraviolet – thermal infrared wavelengths and report on example from certain satellites on the different volcanic features that one can capture.
For the detection of thermal signals, sensors such as the U.S. National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) can provide measurements at approx 1 km and 90 m spatial resolution respectively. For the MODIS sensor, it is aboard two NASA satellites and as such there are generally four overpasses per day, more in Polar Regions.
ASTER data is collected through a tasked system and as such, for volcanoes, is not routinely collected. Other useful sensors include the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) and Visible Infrared Imaging Radiometer Suite (VIIRS), NASA Advanced Land Imager (ALI) and United States Geological Survey (USGS) LANDSAT-8 sensors.
Figure 1 shows some examples, from my blog, http://volcanodetect.blogspot.com/, where thermal signals have been detected in the data from these sensors. Harris (2013) provides an excellent overview of thermal detection of volcanic features.Figure 1A, is an ASTER image of Shiveluch volcano from March 4, 2014 (http://volcanodetect.blogspot.com/2014/03/aster-imagery-of-shiveluch-volcano.html). Here in the thermal infrared range, the temperatures are from +19 to -20 C, hence the ‘white’ and more elevated region close to the summit of the volcano.
Figure 1B is a LANDSAT-8 view of Pacaya volcano from March 3 2014 (http://volcanodetect.blogspot.com/2014/03/pacaya-volcano-march-3-2014-0440-utc.html). This is from Band 10 at 11 µm. Figure 1C shows a NASA ALI image from May 18, 2013 of Pavlof volcano. This is a Red-Green-Blue (RGB) view of the visible channels, illustrating the thermal signals from the volcanic activity and the water/steam and volcanic ash. Figures 2 and 3 show some examples of the different volcanic ash cloud examples that are possible from the different satellite sensors. Prata (1989), Pavolonis and Sieglaff (2010) and Webley et al. (2009) are just three example of the brightness temperature difference (BTD) methodologies applied for the detection of volcanic ash clouds, using TIR data. Figures 2 and 3 are examples from AVHRR data from the 2006 eruption of Augustine volcano (Bailey et al., 2010) and the 2009 eruption of Redoubt volcano (Webley et al., 2013).
There are also methods that can be applied to compare RGB imagery to that from the different TIR bands. The example highlighted here is for the 2014 eruption from Sinabung volcano, Indonesia. The data in Figure 4 is from NASA ASTER and was collected at 03:56 UTC, or local daytime. Figure 4A shows the RGB imagery of the Visible-Near IR (VNIR) channels from Bands 3, 2 and 1 in ASTER. Compare this to the decorrelation stretch using the TIR data from bands 14, 12 and 10 in RGB and the ash is highlighted, Figure 4B. This tool is useful at local night-time, when the RGB data in Figure 4A would not be available. This data can be seen at my blog entry, http://volcanodetect.blogspot.com/2014/02/aster-imagery-of-sinabung-volcano.html
In addition to the detection of volcanic ash, volcanic gases such as sulfur dioxide, SO2, can be recorded from space, both in the TIR and the ultraviolet. Figure 5 illustrates two examples, one from the 2009 eruption of Redoubt volcano using NASA Ozone Monitoring Instrument (OMI) data in the ultraviolet, Figure 5A, and another example using a MODIS decorrelation stretch on the 2009 eruption of Sarychev Volcano, Russia, Figure 5B. These two sensors have very different spatial resolutions and so the OMI data looks ‘blocky’ in comparison to the MODIS data.
For satellite remote sensing of volcanoes, one can also measure in the microwave wavelength range. This time, the data comes from an active sensor, where a radar pulse is sent to the surface and the time to return to the satellite is record. Using this information, with the wavelength of the sensor, and orbital information, one is able to record the altitude of the ground surface to mm accuracy; Figure 6A shows an example from Merapi volcano of the dome at the summit of the volcano. Combining multiple images together and one is able to watch the change overtime from radar data, analyzing subtle changes in mm to m/yr. This data and methodology, known as satellite synthetic aperture radar (SAR) interferometry (InSAR), see Hanssen (2001), then is critical for mapping small scale changes at a volcano, which could then lead to large eruptive events. Figure 6B shows how, from Lu (2002; 2007), that InSAR measurements can be used to map out up to 17 cm of uplift at Peulik volcano in Alaska from 1996 – 1997.
In this report here, the use of webcam imagery, thermal cameras and satellites and their sensors has been highlighted for remote sensing of active volcanoes. Ground based measurements are useful as they can provide continuous views of the volcano and their activity. Short term campaigns can provide more data that can be used to calibrate/validate the long term ground instruments. But not all volcanoes can have a webcam/thermal camera, and so satellite data has been used to analyze in real-time volcanic activity. Whilst not always being able to see the volcano as it erupts, the change over time can be use for those in hazard assessment and to detect significant changes that could lead to large scale activity.
Dr. Peter Webley is an Assistant Research Professor at the Geophysical Institute, University of Alaska Fairbanks. Dr. Webley’s focuses upon using remote sensing data to analyze natural hazards, such as volcanic events, forest fires, landslides and coastal erosion. Dr. Webley has designed new mechanisms to visualize the development of volcanic ash clouds. He has taken the three-dimensional dispersion model simulations that used to be visualized on two-dimensional maps and displayed them in their original three-dimensional form. Dr. Webley has been the guest editor for two special issues of the Journal of Volcanology and Geothermal Research (JVGR) in 2009 and 2013. His paper collaborating on eruption source parameters, Mastin et al. (2009) and listed in his selected publications is the highest cited publications in JVGR since 2008 with over 95 citations.
Recently in 2013, Dr. Webley, along with Dr. Jon Dehn, an Associate Research Professor at the Geophysical Institute, University of Alaska Fairbanks, formed a company called V-ADAPT, Inc [Volcanic Ash Detection Avoidance and Preparedness for Transportation], (www.vadapt.net), from their research at the University in analysis of volcanic activity and dispersion modeling of volcanic ash clouds. V-ADAPT, Inc. provides data, tools, analysis, and risk assessment of volcanic ash for the aviation and other transportation industries. They offer a comprehensive system to help in planning and response to volcanic eruptions for its clients. It is based on over 20 years of the founders’ experience in mitigating hundreds of eruptions in the North Pacific. The company focuses on volcanic hazard assessment and scenario planning through research and development, consultancy and service-orientated web-based tools.
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Webley, P. W., Lopez, T.M., Ekstrand, A. L, Dean, K. G., Rinkleff, P., Dehn, J., Cahill, C. F., Wessels, R., Bailey, J. E., Izbekov, P., and Worden, A., 2013. Remote observations of eruptive clouds and surface thermal activity during the 2009 eruption of Redoubt volcano. Journ. of Volc. and Geo. Res., 259, 185-200, http://dx.doi.org/10.1016/j.jvolgeores.2012.06.023