PrintJust as digital cameras have replaced film cameras for many of us on the ground, digital sensors are replacing cameras for aerial surveys. This section describes two sources of digital panchromatic imagery with sufficient geometric resolution for some, though certainly not all, large-scale mapping tasks. Also considered is a panchromatic sensing system with sufficient radiometric resolution to detect from space the light emitted by human settlements at night.
KVR-1000 / SPIN-2
High-resolution panchromatic image data first became available to civilians in 1994, when the Russian space agency SOVINFORMSPUTNIK began selling surveillance photos to raise cash in the aftermath of the breakup of the Soviet Union. The photos are taken with an extraordinary camera system called KVR 1000. KVR 1000 cameras are mounted in unmanned space capsules very much like the one in which Russian cosmonaut, Yuri Gagarin, first traveled into space in 1961. After orbiting the Earth at altitudes of 220 kilometers for about 40 days, the capsules separate from the Cosmos rockets that propelled them into space, and spiral slowly back to Earth. After the capsules parachute to the surface, ground personnel retrieve the cameras and transport them to Moscow, where the film is developed. Photographs are then shipped to the U.S., where they are scanned and processed by Kodak Corporation. The final product is two-meter resolution, georeferenced, and orthorectified digital data called SPIN-2 (Space Information 2-Meter). A firm called Aerial Images, Inc. was licensed in 1998 to distribute SPIN-2 data in the U.S (SPIN-2, 1999).
© 2006 Aerial Images, Inc. All rights reserved. Used by Permission.
IKONOS
Also in 1994, when the Russian space agency first began selling its space surveillance imagery, a new company called Space Imaging, Inc. was chartered in the U.S. Recognizing that high-resolution images were then available commercially from competing foreign sources, the U.S. government authorized private firms under its jurisdiction to produce and market remotely sensed data at spatial resolutions as high as one meter. By 1999, after a failed first attempt, Space Imaging successfully launched its Ikonos I satellite into an orbital path that circles the Earth 640 km above the surface, from pole to pole, crossing the equator at the same time of day, every day. Such an orbit is called a sun synchronous polar orbit, in contrast with the geosynchronous orbits of communications and some weather satellites that remain over the same point on the Earth's surface at all times.
© 2001 Space Imaging, inc. All Rights Reserved. Used by permission.
Ikonos' panchromatic sensor records reflectances in the visible band at a spatial resolution of one meter, and a bit depth of eleven bits per pixel. The expanded bit depth enables the sensor to record reflectances more precisely, and allows technicians to filter out atmospheric haze more effectively than is possible with 8-bit imagery. Archived, unrectified, panchromatic Ikonos imagery within the U.S. is available for as little as $7 per square kilometer, but new, orthorectified imagery costs $28 per square kilometer and up.
A competing firm called ORBIMAGE acquired Space Imaging in early 2006, after ORBIMAGE secured a half-billion dollar contract with the National Geospatial-Intelligence Agency. The merged companies were called GeoEye, Inc. In early 2013, GeoEye was merged into the DigitalGlobe corporation. A satellite named GeoEye-1 was launched in 2008 and provides sub-meter (0.41 meter) panchromatic resolution (GeoEye, 2007). In 2013, a new satellite named GeoEye-2 became operational. It had a panchromatic resolution of 0.34 meters.
DMSP
The U.S. Air Force initiated its Defense Meteorology Satellite Program (DMSP) in the mid-1960s. By 2001, they had launched fifteen DMSP satellites. The satellites follow polar orbits at altitudes of about 830 km, circling the Earth every 101 minutes.
The program's original goal was to provide imagery that would aid high-altitude navigation by Air Force pilots. DMSP satellites carry several sensors, one of which is sensitive to a band of wavelengths encompassing the visible and near-infrared wavelengths (0.40-1.10 µm). The spatial resolution of this panchromatic sensor is low (2.7 km), but its radiometric resolution is high enough to record moonlight reflected from cloud tops at night. During cloudless new moons, the sensor is able to detect lights emitted by cities and towns. Image analysts have successfully correlated patterns of night lights with population density estimates produced by the U.S. Census Bureau, enabling analysts to use DMSP imagery (in combination with other data layers, such as transportation networks) to monitor changes in global population distribution.
