SAN FRANCISCO — For decades, space-based instruments have provided scientists with detailed imagery of volcanic eruptions and helped researchers trace the movement of the ensuing ash clouds. Increasingly, researchers are investigating whether satellites could be used to help researchers detect signs that volcanic activity may be imminent.
On Aug. 18, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (NPP) weather and climate satellite spotted unusually high temperatures as a result of an upsurge in volcanic activity in Japan’s Mount Sakurajima. That high thermal reading was noted 14 hours before Mount Sakurajima erupted, spewing ash over nearby Kagoshima city.
Researchers caution that while VIIRS did detect rising temperatures in Mount Sakurajima, a single instrument on a polar-orbiting satellite is unlikely to provide much help in pinpointing global volcanoes on the verge of eruption. A variety of satellite instruments carried on geostationary and polar-orbiting spacecraft coupled with ground-based instruments and observations, however, may improve forecasts of volcanic activity.
VIIRS scans scenes in 22 wavelength bands, including a visible channel known as the day-night band, which is designed to identify sources of heat such as gas flares and volcanoes. The day-night is designed to obtain imagery in conditions ranging from bright sunlight to scarce light by amplifying light sources in individual pixels when necessary.
The first VIIRS instrument was launched on NPP in October 2011. NASA and NOAA plan to fly two additional VIIRS sensors on the Joint Polar Satellite System-1 spacecraft, scheduled for launch in 2017, and JPSS-2, scheduled for liftoff in 2021.
The VIIRS day-night band might be able to detect changes in surface heat signaling an imminent volcano, said William Straka, an atmospheric scientist at the University of Wisconsin’s Cooperative Institute for Meteorological Satellite Studies in Madison. “It is theoretically possible,” Straka said. “You might detect a small change in the temperature of the ground but it would have to be detected at a time when you were not getting regular daytime heating of the surface of the Earth.”
Moreover, VIIRS’s host satellite, NPP, travels in a polar orbit, circling Earth approximately 14 times per day. Unlike a geostationary satellite, it is not focused on a single area of the globe. “You cannot move the satellite into the right position to track one particular volcano,” Straka said. Spotting a volcano on the verge of eruption is “the luck of the draw.”
Still, thermal imagery could offer an indication of possible underground volcanic activity, as could visible imagery showing a rapid decrease in snow cover near dormant volcanoes. The most accurate way to forecast volcanic activity would be to couple that information with seismic sensors.
“If you rely on one source of information too much, you end up with a case of false detection,” Straka said. “Then people no longer believe you.”
Space-based radars provide another source of data on volcanic activity. Estelle Chaussard, a NASA graduate fellow in the active tectonic group at the University of California, Berkeley, used data drawn from the interferometric synthetic aperture radar flown on the Japan Aerospace Exploration Agency’s Advanced Land Observing Satellite (ALOS) to “detect centimeter scale ground deformation that typically characterize pressurization of a magma reservoir due to the arrival of new magma or the exsolution of gases.”
That type of deformation indicates that volcanoes are likely to erupt in the near future, Chaussard said by email. “Knowing which volcanoes deform could help constrain where ground based instrumentation should be deployed to successfully predict volcanic crises,” she added.
Chaussard and her colleague Falk Amelung of the University of Miami Rosenstiel School of Marine and Atmospheric Science in Florida used observations made by the L-band synthetic aperture radar on ALOS to study volcanoes in Indonesia and Mexico. The ALOS L-band sensor offered global coverage and its ability to make measurements in areas of dense vegetation, Chaussard said.
Launched in 2006, ALOS stopped gathering data in 2011 due to a power failure. Its successor, ALOS-2 is scheduled to fly in 2014. The L-band sensor built for ALOS-2 also is designed to detect land surface changes, including the ones that are characteristic of volcanic activity. However, because the satellite obtains imagery of specific areas only once every 14 days, it is not likely to be of significant use in volcano monitoring.
In contrast, planned NASA Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) mission and the German DLR’s TanDEM-L mission “should provide the high-temporal and L-band high-spatial resolution imagery needed to advance the assessment of geological hazards,” Chaussard said.
TanDEM-L is expected to launch in 2019 and DESDynI is slated for a 2021 launch.