Special Assignment

Special Assignment

Remote sensing, or the detection of surface-material properties such as composition and texture without physical interaction with the material, is an important analytical approach and tool for investigating and monitoring processes taking place on and within the earth's surface.

For many Earth scientists, remotely sensed data is synonymous with satellite images. Remotely sensed data typically is collected by automated sensors on satellites in high polar and sun-synchronous orbits at approximately 700-900 kilometers (around 435 to 560 miles) altitude above the earth's surface. The field of Earth (or terrestrial) remote sensing is rooted in the early days of the space race. "Spy satellites" have collected imagery - some of which is now declassified - since the beginning of the space program in the late 1950s. Civilian Earth-observing satellites have been operational since 1972. Today, the collection of publicly available, remotely sensed data is an important asset for scientists. If you ask a geologist, ecologist, geographer, or other natural scientist to name datasets used for terrestrial remote sensing, he or she most likely will mention a number of satellite-based sensors known by acronyms such as the Landsat ETM+, MODIS, IKONOS, SPOT, or ASTER (ETM+: Enhanced Thematic Mapper Plus; MODIS: Moderate Resolution Imaging Spectroradiometer; SPOT: Système Probatoire d' Observation de la Terre; ASTER: Advanced Spaceborne Thermal Emission and Reflection Radiometer).

ASTRONAUT IMAGES

Another remotely sensed dataset is available for terrestrial studies and applications such as urban planning: photographic images of the earth taken by astronauts from the Gemini missions of the 1960s to the present International Space Station (ISS) crews. (I focus here on imagery collected by the U.S. Space Program; similar data collection was sponsored by the former Soviet Union Space Program from the mid-1960s to the present.) The astronaut photography dataset covers much of the earth's land and coastal surface, as well as atmospheric phenomena such as hurricanes and aurora. Unlike the satellite-based sensors mentioned above, astronauts use off-the-shelf film and digital cameras to image the earth, rather than mission-specific instruments. Such equipment limits astronaut photographs to the visible and near-infrared wavelengths in three bands (red, green, blue, and near-infrared with appropriate filters), similar to what is collected by aerial photograph surveys. The majority of astronaut photographs was taken from altitudes of 300 to 400 km (185 to 250 miles) - the most notable exception being the Apollo missions to the Moon during 1969- 1972. Currently the ISS is the primary manned platform for astronaut photography, which is acquired exclusively with digital cameras.

Probably the most significant distinction of astronaut photography as a research dataset is the most obvious one

- these images are framed and acquired by a human being rather than an automated sensor system. A full orbit of the earth takes approximately ninety minutes, during which time the ISS crosses both illuminated and dark portions of the globe. The ISS orbit track shifts westward relative to the earth's surface by the amount of rotation during a full revolution of the spacecraft; groundtrack repeat coverage is around three days within an approximately three-month ...