Month: April 2012

Dr. Sundar Christopher is a Professor in the Department of Atmospheric Sciences at the University of Alabama in Huntsville.  Other positions he hold at the University include Associate Director of the Earth System Science Center and Department Chairman of the Atmospheric Science.  He also hosts a professional development and career guide website, which he freely dispenses valuable advice to graduate students. 

What do you study?

SC: Using satellite data, I study the role of aerosols on climate and air quality.

One of your titles at the University of Alabama is an Associate Director of the Earth System Science.  What is Earth System Science Center (ESSC)? 

SC: At UAHuntsville ,ESS is a broad term for the organization that houses scientists who study Earth-atmosphere processes.

You use CERES and other remote sensing satellites to study aerosols, can you talk about the role it plays on the Earth’s atmosphere system and the importance of the study? 

SC: Aerosols are a key component of the earth’s atmosphere. How aerosols affect climate is still a source of uncertainty. Satellite remote sensing is the only viable method for providing global, reliable measurements of aerosols. Detecting aerosols using multi-spectral, multi-angle methods and using CERES to quantify aerosol forcing is in my opinion one the major advances of aerosol science over the last decade. Now we can also assess the role of absorbing aerosols using OMI and analyze the vertical distribution of clouds and aerosols using CALIPSO. There is much to be done using Terra and A-train data sets.

CERES is also used to study energy balance and like ESS, the study is very complex.  Can you explain what energy balance is and its role in understanding future climate? 

SC: Yes, energy balance is critical. In summary the net incoming solar radiation at the top of the atmosphere must be balanced by the outgoing radiation. CERES is indeed the best available source for providing this information over long time periods. While aerosols are short lived in the atmosphere they change the vertical structure of the atmosphere based on their absorptive properties and reduce solar insolation to the surface, all of which are important to climate. More importantly we have been using Terra data to calculate air quality near the ground which is useful for regions that do not have ground measurements of pollution. The effect of aerosols on clouds continue to be a challenging topic but a lot of progress has been made over the last decade.

Finally, how did you get interested in science?

SC: Believe it or not, I was sitting in a radiative transfer course during my graduate school days and the Professor was lecturing on the global radiative energy budget. I felt the light go on inside my head. That was nearly 25 years ago. I studied the radiative energy budget of clouds using ERBE and I later became interested in aerosols from biomass burning. Our first paper used AVHRR and ERBE data to study radiative forcing of aerosols using a few case studies. I was eagerly awaiting the launch of Terra and it is indeed truly rewarding to be able to provide global estimates of radiative forcing using Terra (from MODIS, MISR, and CERES).

Michael Ramsey

Dr. Michael Ramsey is an Associate Professor in the Department of Geology and Planetary Science at the University of Pittsburgh.  He also heads one of the premier state-of-the-art image analysis centers in the nation, which includes infrared spectroscopy and GPS technologies.  In addition to teaching remote sensing courses to under-graduate and graduate students at the University, he also travels all over the over the world to study volcanoes.

What do you study?

MR: My primary area of study is physical volcanology focusing on eruptions, volcanic processes, and monitoring using thermal infrared (TIR) remote sensing.  Of specific interest to me is the linkage between the renewal of activity at an explosive volcano and the ability of remote sensing to detect that activity and help monitor subsequent hazardous activity.  I have helped initiate a rapid response program using data from MODIS and AVHRR to trigger emergency ASTER observations of volcanoes and other natural disasters.  In addition to the satellite image analysis, the tools employed include laboratory-based infrared spectroscopy, field-based TIR imaging and differential global positioning system (dGPS) data collection. I have focused on the multispectral thermal IR data of ASTER in order to map composition and micron-scale roughness of volcanic surfaces. No other sensor can capture this information, which is important to a better understanding of the activity conditions present at active lava domes and flows.

Why is the study of volcanoes important?

MR: Although volcanoes do not kill as many people as earthquakes or large tropical storms (more than 70,000 deaths from volcanic eruptions occurred last century compared to more than that in just one large earthquake), there are several important reasons to study them. The first is hazard mitigation – over a half a billion people live directly in harms way of typical volcanic activity. This number grows significantly when one considers the much larger (but more rare) eruptions that have happened over time. The second reason is that volcanism is a primary geologic process that has operated throughout most of the Earth’s history (along with impact cratering). For a geologist, studying volcanoes can lead to important insights into the solid Earth processes that have operated over geologic time and are ongoing at depth under every active volcano.

What are some effects of volcanic eruptions on the global climate?

MR: I do not study the climate aspects of volcanic eruptions directly since I am more interested in the geology. However volcanoes can produce large amounts of carbon dioxide, water, and sulfur dioxide as well as ash.  The first two are major greenhouse gases, which can impact climate change. Volcanic ash can cause major disruptions to air traffic (as was seen in Iceland in 2010), can render lands around the volcano unusable for decades, be a major irritant to human health, and can cause structures to fail due to the weight of the ash.

Volcano eruptions disperse gas, liquids, and particles into the lower atmosphere.  One of the expellants is sulfur dioxide (SO2.)  What are the effects on the environment?  
MR: Sulfur dioxide generally does not last for long periods in the atmosphere. However, if mixed with NO2, it can form acid rain. Even directly, its presence can be a major irritant to breathing and kill local vegetation.

Compared to other Earth-observing satellites, what makes ASTER the “œpremiere instrument” to study volcanoes?

MR: There are five critical factors that make ASTER the premiere instrument to study volcanoes. I document these in detail in the Ramsey and Dehn (2004) paper: “œSpaceborne observations of the 2000 Bezymianny, Kamchatka eruption: The integration of high-resolution ASTER data into near real-time monitoring using AVHRR”. First, and perhaps the most critical, is the strategy of routine night time acquisition data for all high-temperature targets. This allows far more data to be collected. Second, ASTER has a cross-track pointing capability, allowing an increased temporal frequency for any target as well as data collection up to 85 degrees latitude. Third, the instrument can generate along-track digital elevation models (DEMs) by way of one backward-looking telescope. Fourth, ASTER data are acquired using one of several dynamic ranges in order to mitigate data saturation over very hot target targets. Finally, ASTER provides more than two bands in the TIR for the first time from space, which is important for compositional mapping of volcanoes.

As a volcanologist, you travel all around the world to study volcanoes.  How do you merge field work and data you collect from ASTER?

MR: ASTER data commonly drives where and how my field work is performed. It can be used as simply as a base map from which to target certain thermal and compositional anomalies for field-based data collection. We also schedule ASTER observations while in the field in order to validate the thermal IR data collected on the ground or to better understand the larger picture of the volcano’s activity over the time when we are there. In a new study, we have merged airborne and ASTER thermal IR data collected from the Shiveluch Volcano, Russia. By comparing the ASTER data over the first six months of the eruption to the thermal IR data collected in the field, we were able to document the volume of the extruded lava dome and how its position changed following the eruption.

Finally, what motivated you to study volcanoes?

MR: I had always been interested in geology since I was a child, however my undergraduate degree was in Mechanical Engineering at Drexel University in Philadelphia. My interest in geology was rekindled there after taking a course in Engineering Geology. I took several more classes in geology and went on to do a Ph.D. in the field at Arizona State University. I was not focused on remote sensing or volcanology when I started there, but ended up with two main advisors (one in remote sensing – Phil Christensen and one in volcanology – Jon Fink). It was a natural progression to merge the two fields and study active volcanic eruptions using thermal IR data. This was a few years prior to the launch of Terra, but once ASTER started returning data it became the best way to study small-scale volcanic processes globally.

Deseasonalized anomalies of global effective cloud-top height from the 10-year mean. Solid line: 12-month running mean of 10-day anomalies. Dotted line: linear regression. Gray error bars indicate the sampling error (±8 m) in the annual average.

Stereo measurements from the Multiangle Imaging SpectroRadiometer (MISR) on the Terra satellite show a decrease in global cloud height between March 2000 and February 2010. MISR records the height of the top, thick cloud (not thin clouds), the cloud layer that has he greatest influence on radiating longwave radiation (heat) to space. Lower clouds radiate more energy than higher clouds, so a drop in cloud height could help counter rising global temperatures. In this analysis, the change in cloud height was calculated by comparing heights for a given 10-day period with the average global height calculated for that time of year over the ten-year period. The greatest change-a drop of 80 meters below average-occurred in 2007 and 2008, during a strong La Niña event. The height difference between the 2000 and 2010 is 31 meters.  The observed trend is strongly influenced by the La Niña event and may disappear over time. If the trend persists, it would represent a strong negative feedback to global warming.


Davies, R. and Molloy, M. (2012, February 3). Global cloud height fluctuations measured by MISR on Terra from 2000 to 2010. Geophysical Research Letters, 39, L03701.

An analysis of data from Terra’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument mapped the thermal characteristics of Hawaii’s Kilauea, Mauna Loa, Mauna Kea, Hualãlai, and Haleakalã volcanoes between 2000 and 2010. Images for all five areas were compiled and stacked to provide time series and temperature trends. Thermal areas were conspicuous on Kilauea, shown here, and Mauna Loa. The image on the right was produced by “œstacking” 42 individual surface kinetic temperature measurements of the Kilauea crater. The only significant change in thermal activity noted in the study period is the opening of the Halema”˜uma”˜u ventat Kïlauea’s summit in 2008. Researchers observed several small thermal anomalies that coincidewith pit craters on Hualälai. The anomalies most like  result from the sheltered nature of the depression, but closer inspection is warranted to determine if genuine thermal activity exists in the craters. Thermal areas were not detected on Haleakalä or Mauna Kea.

Patrick, M.R., and Witzke, C.-N., 2011, Thermal mapping of Hawaiian volcanoes with ASTER satellite data: U.S. Geological Survey Scientific Investigations Report 2011-5110, 22 p., available at