Astronauts on board the International Space Station (ISS) have many tasks, but a consistent favorite is taking photographs of Earth. The ISS astronauts don't just take digital images randomly. The photos they shoot are part of a well-defined program of data collection coordinated through the Crew Earth Observations team at Johnson Space Center. Current research targets include glaciers, deltas, urban areas, coral reefs, megafans (inland deltas), and long-term ecological monitoring sites. Dynamic events such as hurricanes, dust storms, volcanic eruptions, and fires are also imaged when possible. The database of astronaut photography is freely accessible via the Internet.
The Crew Earth Observations team selects science targets and uploads them to the ISS crew daily based on the current orbital position of the ISS, local sun angle, predicted local weather conditions, and the task schedule. Satellites, such as Landsat and Terra, that are in polar (pole-to-pole) orbits pass over the same location on the globe at approximately the same time every day. The inclined (angled), equatorial orbit of the ISS and having a "human in the loop" to point the camera allow for a wide variety of local sun angles and ground resolutions (levels of detail) for science targets. These unique characteristics of astronaut photography provide a dataset that includes both scientific and aesthetic, or artistic, value. This duality is expressed in ISS Expedition 10 Commander Leroy Chiao's ten favorite photos (see also Expedition 10 Earth Observation Photos; and Shooting for the Heart: Astronaut Finds Passion for Photography in Space).
Two of the world's great cities, New York and Beijing, were among those imaged by Leroy Chiao during Expedition 10. Large urban centers such as these serve as global economic, social, and cultural centers. The establishment and growth of cities also alters local and sometimes regional climate patterns, hydrology, and ecology. Replacement of existing soil and vegetation by asphalt and concrete fosters the creation of urban "heat islands," increases surface water runoff, decreases groundwater recharge, and fragments pre-existing ecosystems.
While cities represent people's most visible alteration of Earth's
surface, numerous other regions of the planet are also directly or
indirectly impacted by human activities. Photography of glaciers,
deserts, coastal regions, and lakes provide data for tracking changes.
Astronauts document the advance and retreat of glacial ice due to
climate change; location and structure of dune fields related to
desertification; changes to coastlines and deltas following hurricanes
or human development; and changes to lakes and rivers related to land
cover and land use change. Digital astronaut photographs only record
data in the visible red, green, and blue wavelengths of light (not
infrared, for example), but the variety of acquisition times and
spatial resolutions make these data useful additions to more
traditional multispectral and hyperspectral datasets from satellites
and other remote-sensing platforms like aircraft.
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