Satellite imagery assists research

Some use maps to analyze history, others use them to track weather, while still others are intently watching swing states flicker between red and blue. But, researchers that collaborate with the Center for Earth Observation at Yale use maps for some unusual scientific purposes.

“We study the earth from space,” said Larry Bonneau at the Center for Earth Observation. “We use satellite images to study changes in the landscape and environment.”

Studying satellite imagery of these changes allows scientists to research everything from agricultural systems to diseases transmitted by insects.

Durland Fish, professor of epidemiology at the School of Medicine, said he focuses on using satellite images to analyze and map human risk for insect-borne diseases, specifically Lyme disease. He uses satellite imagery to locate forests where deer that support the potentially infectious ticks live and also analyzes temperature and moisture levels to determine if the ticks can survive in a particular environment.

Ted Holford GRD ’72, who has also worked with data from the Center for Earth Observation, said that in projects in which researchers study vector-bone diseases, satellite mapping is highly useful.

“We try to identify variables that would be available from these other sources, like satellite imagery, and develop models that describe how these things are related to habitats that are friendly to the vectors,” Holford said.

He said the effects of neighboring regions on each other presents a biostatistical dilemma. Some areas can have an impact on data gathered from their surroundings, which raises questions of correlation and independence, he said.

The goal of the research is to present high risk populations with preventative measures, Fish said. He said the research’s purpose is to determine risk levels for different areas and convey this information to both local authorities and individuals.

The West Nile virus, researched at the center by Maria Diuk-Wasser, is studied in a similar fashion. She is building a West Nile virus risk map for the state of Connecticut, analyzing the landscape and weather patterns to determine the location of potentially infectious mosquitoes. Diuk-Wasser’s research includes correlating satellite image features to different mosquito population densities.

But diseases carried by insects are only one topic of research at the center. Frank Hole studies land use in Asia. He said the project focused on land use, the percentage of land covered with vegetation and types of land cover. Hole said he is specifically examining how land use has changed over the past 50 years and how these changes might reflect the effects of population, government policies, economic factors, ethnic mix, and the introduction of technology.

Hole said one of the challenges of using satellite data is that researchers cannot rely purely on the images but must visit and study the locations.

“We have to establish ground truth, so we understand what we are seeing in the imagery,” Hole said.

According to Diuk-Wasser, another two aspects that cannot be overlooked when using satellite data are temporal resolution — how frequently the images are taken — and spatial resolution — the images’ level of detail. She said another issue is availability — researchers need to get “the right images at the right time at the right place.”

Despite the setbacks, researchers said they were optimistic about the new breed of research.

“[Satellite imaging] is a remarkable resource, and it has developed over the last 10 years,” Hole said.

The Center for Earth Observation is available to train students and provide data for student research. According to Bonneau, a course titled “Observing the Earth From Space” is available to train students in remote sensing and utilization of the center and its unusual use of maps.

A map of the northeast created using ArcView GS plots the locations of state parks within quadrants along major highways. Such maps from the Center for Earth Observation at Yale are used by researchers in a variety of projects.
Courtesy DurlandFish
A map of the northeast created using ArcView GS plots the locations of state parks within quadrants along major highways. Such maps from the Center for Earth Observation at Yale are used by researchers in a variety of projects.

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