Introduction

Fifteen years ago this month the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard NASA’s Terra platform began returning images. The first image from ASTER’s thermal infrared (TIR) subsystem was captured on March 3, 2000, and focused on the western edge of the volcanic Afar Triangle in Ethiopia (see image below). This image represents not only ASTER’s first thermal image, but also the first high-resolution, multispectral thermal data collected by a sensor on a satellite. Since this first image 15 years ago, ASTER data has continued to be valuable to geologic and volcanic applications, as well as many other scientific disciplines.

Science Objectives

In Murphy et al., 2013 the authors measure thermal anomalies of four volcanoes, including Erta Ale, an isolated shield volcano located within the Afar Triangle and Ethiopia’s most active volcano. They calculate surface temperature from the high-resolution ASTER imagery and use it along with nighttime calibrated radiance from lower resolution data from the Moderate Resolution Imaging Spectroradiometer (MODIS) also onboard Terra. With these data, the authors were able to determine new locations of thermal anomalies and detect changes in existing anomalies, such as the rise or fall of Erta Ale’s lava lake. The ASTER Volcano Archive also monitors thermal activity at Erta Ale, among other volcanoes, on a consistent basis.

Instruments and Techniques Used

In addition to the TIR subsystem, the ASTER sensor has two other subsystems: the visible and near-infrared (VNIR) and the shortwave infrared (SWIR). The VNIR subsystem is also capable of collecting stereoscopic data, which provides topographic information. Spatial resolution varies among the data that the ASTER sensor captures: VNIR data has 15-meter resolution, SWIR has 30-meter, and TIR has 90-meter. The varying resolutions and data types allow for different aspects of volcano activity to be investigated. For example, the high spatial resolution thermal data from ASTER helps scientists to remotely determine and measure both obvious and subtle thermal anomalies.

Major Findings

The ASTER images below show Erta Ale’s different volcanic features. Erta Ale’s most recent eruption was in 1967, but the eruption has been continuous, leading to smaller fissure eruptions that have produced new lava flows. Erta Ale also has a molten lava lake in its crater. The lava lake is easily detectable and measurable from 90-meter ASTER TIR imagery. Like in the image of Erta Ale from 2000, the white pixels in the TIR image from March 2, 2015 (bottom left), show the extent of the hot lava lake. In the 30-meter VNIR image (bottom right), the lava lake, lava scars from past eruptions, and current lava flows, are differentiated by different shades of black. Scientists can use VNIR images to study past lava flows and construct the eruption history of a volcano.

References

Publication Reference

Abrams, M., Tsu, H., Hulley, G., Iwao, K., Pieri, D., Cudahy, T., and Kargel, J., 2015, The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) after fifteen years: Review of global products: International Journal of Applied Earth Observation and Geoinformation, v. 38, p. 292-301, at doi:10.1016/j.jag.2015.01.013.

Article References

JSS, 2012. Volcano Monitoring Using ASTER: Japan Space Systems (JSS) ASTER Science Project Web page, accessed March 6, 2015.

Murphy, S.W., Wright, R., Oppenheimer, C., and Souza Filho, C.R., 2013, MODIS and ASTER synergy for characterizing thermal volcanic activity: Remote Sensing of Environment, v. 131, p. 195-205, at doi:10.1016/j.rse.2012.12.005.

NASA JPL, [n.d.], Erta Ale: National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) ASTER Volcano Archive Web page, accessed March 2, 2015.

NASA Visible Earth, 2000, Thermal Infrared, Afar Triangle, Ethiopia, accessed March 1, 2015.

SI, 2013, Erta Ale: Smithsonian Institution, National Museum of Natural History Global Volcanism Program Web page, accessed March 2, 2015.

Image References

ASTER VNIR Granule IDs

• AST14OTH_00303022015075628_20150305193034_27227
• AST14OTH_00303022015075637_20150305193034_27225

ASTER TIR Granule IDs

• AST14OTH_00303022015075628_20150305193034_27227
• AST14OTH_00303022015075637_20150305193034_27225