The view from the rim of Mt. St. Helens may be thrilling, but one of the best and safest ways to study volcanoes is from space. New spaceborne instruments let scientists peer deep into volcanoes and learn about their behavior.
"We now have a view toward the center of Earth," says volcanologist Michael Abrams of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Previously, we had to depend on on-site observations not easily accomplished when a volcano was actively erupting. Now we can safely view them from space and obtain fast, accurate information from satellites."
Erupting volcanoes cause casualties, destroy property and devastate local areas. They can also affect regional air quality and visibility with implications ranging from public health to air traffic control. For example, a large eruption by the Popocatepetl volcano near Mexico City has serious consequences for the more than one million people living within 30 kilometers (19 miles) of the volcano.
Now, instruments such as radiometers, spectrometers and interferometers fly far above Earth's surface year-round. They provide scientists with continual coverage of the approximately 500 active volcanoes around the world. The new information they provide makes it possible to do long-term monitoring, develop new research techniques and create detailed images and videos, according to JPL researchers.
Data collected over time can be turned into computer animation that provides dynamic evidence of changes to scientists, government officials and the interested public. "We are pioneering the use of powerful commercial animation software to visualize dynamic volcanic processes such as lava flows, ground deformation, and the appearance and growth of hot spots," says Dr. Vince Realmuto of JPL's Digital Image Animation Laboratory.
The Advanced Spaceborne Thermal Emission and Reflection Radiometer is an imaging instrument flying on Terra, a satellite launched in December 1999 as part of NASA's Earth Observing System. It is being used to obtain detailed maps of land surface temperature, radiation emissions, reflectance and elevation. The instrument helps scientists monitor volcanoes worldwide as they look for unusual thermal features and changes in the output of sulfur dioxide, a major air pollutant that is vented by some volcanoes. Particular attention is currently being directed to Popocatepetl, as well as Kilauea in Hawaii and Mount Etna in Sicily.
Also flying on Terra is the Multi-angle Imaging SpectroRadiometer. Viewing the sunlit Earth simultaneously at nine widely spaced angles, this instrument produces detailed images of Earth in four colors at every angle. These images are carefully calibrated to provide accurate measures of the brightness, contrast and color of reflected sunlight. The instrument can identify even very thin clouds of airborne particles emitted by volcanoes and can sense the cloud height, particle amount and type.
"The multi-angle imaging techniques pioneered by this instrument allow us to detect very small amounts of airborne particles, including volcanic plumes, from space. We can also distinguish non-spherical particles such as mineral dust from pollution and maritime particles, which helps us identify aerosols of volcanic origin," says JPL's aerosol scientist Dr. Ralph Kahn.
The Shuttle Radar Topography Mission, launched on Space Shuttle Endeavour in February 2000, uses a technique called radar interferometry. Differences between two radar images taken from slightly different locations allow for the calculation of surface elevation. According to Dr. Tom Farr, a JPL geologist, "The three-dimensional shapes of volcanoes we get with this data gives volcanologists information on the types of eruptions, ash flow and erosion patterns."
Synthetic aperture radar interferometry data from the European Remote Sensing satellite enables researchers to see how the volcano "breathes," or the changes within and beneath the volcano that cause the surface to expand or contract. "InSAR is one of the keys to revolutionizing our ability to view volcano deformation with complete spatial coverage of almost the entire globe," says Dr. Paul Lundgren, a JPL geophysicist.
The Terra and SRTM missions are included in NASA's Earth Science Enterprise, whose goal is to obtain a better understanding of the interactions between the biosphere, hydrosphere, lithosphere and atmosphere. JPL is managed for NASA by the California Institute of Technology in Pasadena.