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Workshops explore use of satellite imagery, modeling to examine global urbanization

November 02, 2011

How can satellite imagery help us monitor the environmental impact of cities and forecast land use change?

Last spring an international group of experts, together with local government planners and decision-makers, met at ASU to explore this question. Elizabeth Wentz and Soe Myint, professors at ASU, along with Karen Seto of Yale University, ASU’s Michail Fragkias, and Maik Netzband of Ruhr University, organized the gathering.

Satellite images – the views of Earth that we see in online mapping programs and weather forecasts – are the visible representations of information about energy reflected from the earth’s surface, and collected by sensor devices mounted on satellites. Scientists call this approach to collecting information about the earth “remote sensing.”

The original data are actually far richer than the images we see. Scientists can analyze energy in specific wavelengths to measure a whole host of environmental characteristics, from vegetation to temperature to building density. The data behind satellite images can be used as an input to land use forecasting models. The goal of these models is to predict the distribution and intensity of future land use patterns in small, medium or large metropolitan areas.

However, remote sensing analysis and land use forecasting models are at present primarily tools for scientists, not widely used in dealing with short-term or long-term issues of urban growth. At the Urban Remote Sensing and Forecasting Land Use Change (URS/FORE) workshop that took place last April at ASU, participants shared ideas about the challenges associated with urbanization as well as the capabilities of remote sensing technology and forecasting tools.

“In the past, humans occupied predominantly rural areas," said Elizabeth Wentz, associate professor of geography.  "Today, with a shift of employment opportunities to cities, more and more of the world’s population is moving to urban areas. Remote sensing technology provides a powerful tool to observe, monitor and forecast the environmental impacts of this transition.

“The mix of participants in our workshop allowed us to explore ways that remote sensing technology is capable of providing local decision-makers with answers to questions they face daily," Wentz said. "For example, a planner may want to know whether a tree planting and replacement program has been effective at cooling night-time temperatures. Remotely sensed images taken before the program was established through to the present could help answer this question and justify the continuation of the program to budget planners and the general public.”

Research efforts provide other examples of remote sensing as a planning tool. One initiative looks at whether remote sensing can provide information about road condition that can be used to make road maintenance more efficient, targeting roads in need of repair. Another looks at whether remotely-sensed analysis of tree cover can be used to assess the walkability of different areas.  

The workshop participants discussed policy issues needed to make these vision a reality. They noted that while remote sensing data is abundant, it’s not always easy to locate the “right” data for a particular purpose. In addition, software for handling remote sensing data is often expensive and difficult to use for the non-expert.

The two groups (URS and FORE) agreed on the value of several efforts. The first is to improve the accessibility of data by non-expert users, by developing web-based tools for acquiring and working with imagery, using an open-source approach where multiple developers can contribute to building powerful and usable software.

A second effort is to work at creating data archives that store imagery from a variety of sources, for a variety of dates.  

Finally, they agreed that researchers need to study regions in depth, but also need to develop a theoretical framework to tie these case studies together.

“Bringing these groups together generated a momentum in a way that a narrower group couldn’t have done,” Wentz said.

The URS workshop was funded by the National Science Foundation and organized by Maik Netzband from Ruhr-University in Bochum, Germany, as well as Wentz and Myint of ASU’s School of Geographical Sciences and Urban Planning. FORE was sponsored by the National Aeronautics and Space Administration (NASA) and organized through Urbanization and Global Environmental Change (UGEC ) and led by Karen Seto of Yale University and Michail Fragkias of UGEC and ASU.