Remote Sensing Used in Monitoring Active Volcanoes

Cara Haas

ES 771 Remote Sensing Fall 2007

Image taken

Table of Contents
Introduction Satellite Data
Radar Interferometry Ultraviolet Remote Sensing
Conclusions References


Volcanic eruptions are spectacular events and studying these natural phenomena can be an unbelievable journey. But the dangers and constraints of ground observations left a gap for scientist to fill in regards to observing active volcanoes. Remote sensing has increased throughout the last decades and has became a popular tool for observing active volcanoes throughout the world. Remote sensing is the measurement or analysis of properties of the Earth's surface from a location not in physical contact with the objects in view (USGS 2006). There are numerous active volcanoes on planet Earth, monitoring all of these volcanoes can be a task, therefore numerous techniques of remote sensing contributes to accurately collecting data and observations.

Using Satellite Data

New developments in remote-sensing techniques have expanded the capability of scientists worldwide to monitor volcanoes using satellite. Two types of satellites are used for monitoring active volcanoes. One is known as "geostationary" while the other satellite is known as "low Earth orbit". Satellites are used for six main objectives in regards to volcanic eruptions: 1) Rapid detection of an eruption plume, 2) monitoring thermal energy emitted from the volcano, 3) large area mapping of surface deformation of a volcano, 4) measurment of volcano topography and topographic change, 5) illustrating spatial distibution of ash, gases and aerosols produced by eruptions, and 6) referencing a data set for each volcano for quantifying of future changes (Johnson et. al 2000). One of the objectives is to illustrate the spatial distribution of the eruption cloud. This can be carried out through the use of satellite imagery. When a volcano erupts it emits a massive amount of gases into the atmosphere immediately heating the air above the opening of the volcano. With time, the eruption cloud is moved by wind patterns and spreads out over an area. The movement of volcanic emissions can have short-lived impacts or can have effects that last for several years. This process can have impacts on weather and climate over local or global areas affecting overall climate variability.

The image to the left shows the eruption cloud approximately 1.5 hours after the actual eruption occurred. The blue color portrays warm temperatures whereas the red color illustrates colder temperatures.

Image taken from:

The image to the left was taken approximately 3 hours after the actual eruption. Notice the size of the eruption cloud compared to the size of the cloud in the image above. Again, the blue color represents warm temperatures and the red color illustrates colder temperatures.

Image taken from:

Using Radar Interferometry

Volcanic processes can occur far below the Earth's surface, therefore not being visible to the naked eye. Thus, radar provides a new tool to help study and understand the structure of a volcano. Radar interferometry is used for two main reasons: 1) to examine the topography of a volcano and 2) to map surface changes such as lava flows or deformations. This helps in providing a safe enviornement as well decreasing the amount of on-site information needed. This allows researchers to study volcanoes in all types of enviornments. Interferograms are the result of two radar images combined, differentiated only by time. These images can locate magma flow by mapping surface deformations, which assist in monitoring and analyzing subsurface activity. Radar is more widely used because there are fewer restrictions on the actual image taking process. Radar is able to penetrate clouds, therefore there are fewer limitations on the time of day or altitude that the radar process is carried out. Monitoring hotspots is an example of how radar is used in monitoring volcanic activity. Impacts of volcanic eruptions can affect homes, populations, agriculture use, etc. Thus, predictions of potential volcanic activity can be produced in a timely fashion, essential for hazard alertness. Radar interferomtery provides complete spatial coverage from space therefore can provide forecast and predictions of volcanic activity before the eruption occurs.

The image to the left illustrates a monitoring image of a hotspot. The red color portrays an area where deformation is occuring. This could mean volcanic activity is occuring beneath the Earth's surface such as a magma chamber shift. The yellow dot represents the actual hotspot.

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Ultraviolet Remote Sensing

Ultraviolet Remote Sensing is used to produce measurements and data of volcanic emissions during the actual eruption. Thus, Ultraviolet remote sensing can be used to monitor the emissions of sulfur dioxide and ash contents emitted into the atmosphere as volcanic clouds. This technqiue for monitoring eruptions provides a safe environnment to view and model volcanic clouds. Ultraviolet remote sensing maps atmosphere components rather than just photographs an active volcano. Data collected from this type of Remote Sensing helps in calculating sulfur budgets, tracking volcanic clouds and can estimate the volcanic eruptions impacts on the earth's atmosphere. The instrument used during Ultraviolet processes is known as the Total Ozone Mapping Spectrometer or TOMS. This instrument is a ultraviolet spectrometer that monitors the ozone and fluctuating trends of the atmosphere by measuring reflectance and scattering using six different wavelength bands. This is done by measuring temperature variations. Most of the impacts close to the eruption itself such as lava flows, landslides, etc. can be observed by photographs, but the gases emitted from an active volcano can have impacts on the climate and weather long after the actual eruption occurs. Here TOMS is used to observe the amount of emissions and their impacts on the Earth's atmosphere. An example of this process is the conversion of sulfur dioxide into sulfate aerosols once emitted into the atmosphere. This type of volcanic aerosol can impact the atmosphere's chemistry and global climate by increasing atmospheric albedo, the reflection of solar radiation or modification of greenhouse gases. The Total Ozone Mapping Spectrometer can observe these impacts and also help predict future climate and weather fluctuations. The first time TOMS was used to accurately detect sulfur dioxide in the atmosphere was after the eruption of El Chichon, Mexico in 1982.

The image to the left is of the sulfur dioxide cloud emitted from the 1982 eruption of El Chichon, Mexico. The image is portraying the drift of the aerosols four days after the actual eruption.
Image taken from:"Remote Sensing of Active Volcanism".


Volcanoes differ from other natural hazards because they are located in fixed-areas. This is an advantage for the use and accuracy of remote sensing applications with regards to active volcanoes. Remote sensing is able to monitor volcanoes in the most isolated areas without extensive manpower. Without the need for personnel to perform on-site obervations the endangerment to human life has been minimized. Though remote sensing has helped in many aspects of data collecting, the ability to gather data directly from a satellite has improved the timely fashion of studying volcanic eruptions. Before the use of remote sensing in active volcanism, scientists had to gather on-site data and process the data; eventually producing images and models. Now, with the snap of image from a satellite instrument, the events taking place internally and externally of a volcano can be observed in a matter of minutes. As this website discusses, remote sensing has had a major impact in contributing to the understanding and predicting the life of active volcanoes. This will not only save time, lives and resources but can also help in predicting the future of our planet.

If interested in the active volcanoes of today's world click on the following website:


Hawaii Institute of Geophysics and Planetology. "About our GOES 9/10/12 Image Products". URL:

Mouginis-Mark, Peter J., Joy A. Crisp, Jonathan H. Fink. 2000. "Remote Sensing of Active Volcanism". American Geophysical Union. pgs. 272.

Robock, Alan and Clive Oppenheimer. 2003. "Volcanism and the Earth's Atmosphere". American Geophysical Union. pgs 360.

USGS. 2000. "Monitoring Volcanic Gases: the driving force of eruptions". URL:

USGS. 2001. "Detecting Eruption Clouds with Weather Satellites". URL: