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Satellites, Non-Governmental High Resolution

High-resolution satellites, generally understood to be those with a spatial resolution of 2 meters (6.6 feet) or less, have the capability to provide forensic information from areas that are otherwise inaccessible to law enforcement officials.

Resolution is a measure of the ability of an image to depict detail. When used in reference to digital images such as those produced by remote sensing satellites, resolution generally refers to size of the pixels, or fundamental elements, comprising the image. A 2-meter resolution image consists of elements representing the average color or intensity of a 2x2 meter area of Earth's surface. Nothing smaller than 2x2 meters will be depicted as a distinct object. The smallest objects that can be clearly identified on an image, however, will be much larger than the resolution because many pixels are required to represent the characteristic shape or outline of an object. A 2-meter resolution satellite image might, therefore, show distinct images of buildings covering tens or hundreds of square meters, but not a small shed or automobile covering an area the size of a 2x2-meter pixel.

The best commercial satellites operating in 2005 had resolutions of 1 meter (3.3 feet) or less. However, intelligence satellites operated by the U.S. government were believed to have a resolution of about 2 centimeters (0.8 inches). Images with that resolution, however, have never been released for public use.

The first remote sensing satellites were built, launched, and operated by government agencies in the 1960s. In the interest of national security, images from these satellites were tightly controlled and generally inaccessible to civilian officials and forensic scientists. Imagery from the first Landsat satellites, launched by the United States in the 1970s, was publicly available but its low resolution (tens of meters) made it useful only for regional studies. After an attempt to privatize and eliminate government subsidies for the Landsat program in the 1980s, the United States passed the Land Remote Sensing Policy Act of 1992. This act emphasized the importance of satellite imagery, returned the Landsat program to government operation, mandated that its data be made available at cost, and included a provision for the licensing of commercially operated remote sensing satellites. At about the same time, the French government developed the SPOT (Satellite Pour l'Observation de la Terre) program and marketed its imagery through a subsidized corporation. Like Landsat imagery, however, SPOT imagery generally did not provide the resolution necessary for detailed forensic work.

The Landsat and SPOT satellites paved the way for a new generation of high-resolution commercial satellites that provide images detailed enough for forensic work. The commercial IKONOS satellite, launched by the multi-national Space Imaging consortium in 1999, orbits Earth at an altitude of 680 kilometers (422.5 miles) and provides panchromatic (black and white) images with 1-meter resolution. The EROS A1 satellite, built by the ImageSat International consortium in Israel and launched from Russia in 2000, provides 1.8-meter (6-foot) resolution. Its successor, the EROS B1, will have 0.70-meter (2.3-foot) resolution when operable in 2006. The highest resolution commercial satellite imagery available in 2005 came from the QuickBird satellite operated by the Colorado company DigitalGlobe. QuickBird produces 0.62-meter (2-foot) resolution panchromatic images and 2.4-meter (7.9-foot) resolution color images. The panchromatic images, in particular, are detailed enough to depict individual automobiles, pieces of machinery, or ground disturbance associated with illegal activities.

Panchromatic images have higher resolutions (smaller pixel size) than color, or multi-spectral, images. This is because digital imaging sensors have a fixed number of photosites that respond to light. When a panchromatic image is made, each photosite senses the total intensity of light. When a multi-spectral image is made, in contrast, the photosites must be divided among the spectral bands being depicted. Thus, a color image consisting of infrared, red, green, and blue bands would have one-fourth the resolution of a panchromatic image from a sensor with the same number of photosites.

One particularly high profile application of commercial high-resolution satellite imagery was the search for debris from the space shuttle Columbia, which exploded over Texas in 2003. The QuickBird satellite was immediately redirected to cover the accident area, and the resulting images showed areas of broken trees and highly reflected debris. The detailed satellite images allowed accident investigators to better document the extent of the debris field and recover pieces of the shuttle.

High-resolution commercial satellite imagery is also invaluable in the aftermath of natural disasters such as the 2004 Indian Ocean tsunami. There, it was used to help guide relief efforts and provided important information for researchers studying the effects of tsunamis.

Other applications of commercial satellite imagery in forensic science are less exotic. Government officials in Arizona, Georgia, and Minnesota have used satellite imagery to detect illegal cotton cultivation, logging, and pollution. Because satellites pass over any given location no more frequently than every few days, they are best suited for the characterization of slow processes such as growing crops or persistent problems such as air or water pollution. For the same reason, it is unlikely that satellite imagery will provide images that catch thieves, kidnappers, rapists, or murderers committing crimes.

Like photographs and videotapes, satellite images can be manipulated and must therefore be authenticated for use in court. Prosecutors or plaintiff's attorneys must establish that any processing or enhancement techniques used on the imagery were properly documented and followed accepted professional standards, whereas defendant's attorneys may question the authenticity of imagery used against their clients. Although some manipulation must be done in order to transform digital information into a visible image, it is critical to establish that the manipulation did not distort or otherwise misrepresent the area being depicted in the imagery.

see also Digital imaging; Geospatial Imagery; GIS.

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Satellites, Non-Governmental High Resolution

WILLIAM C. HANEBERG

Satellite imagery at resolutions useful for military and intelligence purposes has historically been available only from satellites developed, launched, and operated by governments. As a result, access to and dissemination of the high-resolution satellite images was tightly controlled in the interest of national security. Since 1999, however, commercial satellites have made high-resolution images publicly available at a relatively low cost. In the United States, the Land Remote Sensing Policy Act of 1992, which was motivated in part by Russian willingness to sell declassified 2 m resolution military satellite imagery in the early 1990s, provided the legal foundation for private ownership of American remote sensing satellites. In 1994, the Clinton administration issued guidelines for the licensing of commercial remote sensing satellite operations.

The resolution of an image is the size of the smallest object that can be depicted, and the best images currently available from commercial satellites have resolutions ranging from 50 cm to 1 m. Imagery from the most recent intelligence satellites launched by the United States government, in contrast, is believed to have a resolution of about 2 cm. No images with this resolution, however, have been released to the public. Although there is no universally accepted definition of "high resolution," in part because its meaning changes as technology improves, at the time this article was written it was generally understood to mean resolutions of 2 m or less.

IKONOS, named after the Greek word for "image," was the first commercial satellite to provide images with 1 m resolution. Its products include 1 m panchromatic (black and white) and true color images in addition to 4 m multispectral imagery. Following a sun-synchronous orbit 680 km above Earth's surface, IKONOS passes over any given longitude at about 10:30 a.m. local time each day and revisits any given geographic location every three days. Space Imaging, the company that operates IKONOS

was founded by a consortium of firms from the United States, Japan, and South Korea. The satellite was launched in August 1999 after the first version was destroyed when its launch vehicle malfunctioned and crashed the previous spring.

Developed by an international consortium of companies based in Cyprus and known as ImageSat International (ISI), the EROS A1 satellite was built largely in Israel and launched in 2001 from a Russian facility in Siberia. It was the first high-resolution commercial satellite developed outside of the United States. The EROS A1 camera, which can provide 1.8 m resolution panchromatic images, is

based on technology originally developed for Israeli intelligence satellites. The successor the EROS A1, known as the EROS B1, is scheduled for launch in late 2004 and is expected to produce both panchromatic and multi-spectral color imagery with 0.87 m resolution.

The highest resolution commercial imaging satellite currently in operation is QuickBird, operated by the Colorado-based firm Digital Globe, which follows a sun-synchronous orbit 450 km above Earth. The first QuickBird was lost in space after a late 2000 launch from a Russian facility in Siberia. A replacement was successfully launched from Vandenberg Air Force Base, California, atop a Delta II launch vehicle in late 2001. QuickBird supplies 0.62 m resolution panchromatic images and 2.4 resolution multispectral color images.

Proponents of commercial high-resolution imaging satellites argue that their images will be useful for a variety of civil work that includes infrastructure monitoring, natural disaster recovery, endangered species habitat identification and monitoring, and natural resource exploration. Commercially available high-resolution images can also be used to monitor troop and equipment movement, observe construction activity, identify targets in inaccessible areas, and remotely assess battle damage. This has led the United States government to prohibit its licensees from obtaining or selling high-resolution imagery of Israeli territory in response to concerns raised by the government of Israel. It also reserves the right to restrict operations during times of national security emergencies. These restrictions do not apply, however, to commercial satellites operated by companies outside of the United States.

FURTHER READING:

BOOKS:

Bossler, John D., John R. Jensen, Chris McMaster, and Chris Rizos (editors). Manual of Geospatial Science and Technology. Mount Laurel, New Jersey: Taylor & Francis, 2001.

Campbell, James B. Introduction to Remote Sensing (3d edition). New York: Guilford Press, 2002.

ELECTRONIC:

Baker, J.C. "Commercial Observation Satellites: A Catalyst for Global Transparency." 2002. <http://www.imagingnotes.com/julaug01/global.htm> (12 April 2003).

"Digital Globe." <http://www.digitalglobe.com/> (12 April 2003).

"ImageSat International." 2003. <http://www.imagesatintl.com/> (12 April 2003).

"Space ImagingVisual Products. Visible Results." 2003. <http://www.spaceimaging.com/> (12 April 2003).

SEE ALSO

Cameras
Geospatial Imagery
LIDAR (Light Detection and Ranging)
Photographic Resolution
Photography, High-Altitude
Remote Sensing

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satellite, artificial Artificial object placed in orbit around the Earth or other celestial body. Satellites can perform many tasks, including sending back data or pictures to the Earth. Hundreds of satellites of various types orbit the Earth. They may study the atmosphere, or photograph the surface for scientific or military purposes. Communications satellites relay radio, television, telephone, telegraph, and data signals from one part of the Earth to another. Navigation satellites transmit radio signals that enable navigators to determine their positions. The global positioning system (GPS) uses satellites in this way. Geodetic satellites are used to make accurate measurements of the Earth's size and shape. Sputnik 1 was the first artificial satellite, launched on October 4, 1957.