Multi-sensor Approaches to Urbanization: Using Astronaut Photography of Earth to Fill Data Gaps

Scientists studying the rapid growth of urban areas around the globe often must combine a variety remote sensing sources to get data that meets their needs. Depending on research questions, these needs may include observations at specific points in time or with sufficient spatial resolution. Though not widely used for urban studies, astronaut photography can uniquely fill some data gaps. Early photographs taken during the Gemini and Apollo programs in the 1960s represent the oldest remotely sensed records for a number of world cities. The archive of astronaut photography of Earth is maintained in a single location, offers valuable information on urban boundaries over the last 40 years, and can fill gaps in time series studies. Although working with digitized photographs differs from satellite data, such images can be used as 3-band data, georeferenced, and used with image analysis techniques such as supervised classification and texture analysis. The results of simple land cover classifications can approximate results that would be obtained from Landsat. Using digital cameras from the International Space Station, astronauts are now routinely acquiring photographs of urban areas with 6 m or better spatial resolution. These images serve as valuable sources of information that can be analyzed directly or used to verify analyses of other sensor data. Astronaut photographs of cities are available for public searching on the web at NASA Johnson Space Center's "The Gateway to Astronaut Photography of Earth." The site includes tools for searching the over 400,000 photographs taken to date as well as a special collection, "Cities from Space," of outstanding city photographs.