By J.R. Wilson
LONGMONT, Colo. — Images from a new agile bus satellite using a dual sensor "pushbroom" scanning array and orthorectification to reduce image distortion not only are helping with airport development, management, and maintenance, but also may help airport operators enhance facility security.
Images from the QuickBird satellite, launched by DigitalGlobe in Longmont, Colo., in October 2001, first became available to the global commercial marketplace in May 2002. In July, Grafton Technologies Inc. in Newburyport, Mass., began using QuickBird imagery to map airport features at the Portland International Jetport in Portland, Maine.
"Airports throughout the world are undergoing substantial changes to accommodate higher capacity and stronger security without sacrificing safety," says Grafton president Randy Murphy. "QuickBird imagery can help airport managers, engineers, and planners stay up to date on the information necessary to develop, operate, and maintain rapidly changing facilities.
"Many airports cannot afford traditional aerial photography as frequently as they need it," Murphy continues. "QuickBird satellite imagery offers an affordable, high-resolution option for gathering airport spatial data on a regular basis."
DigitalGlobe officials claim that QuickBird provides the highest resolution satellite imagery available to the commercial market (61 centimeters), the broadest swath width, the highest accuracy, the highest collection capacity, and an imaging footprint as much as 10 times larger than any other commercial high-resolution satellite.
"The implications for the use of high-resolution space imagery are far-reaching," says DigitalGlobe president and CEO Herb Satterlee. Grafton Technologies officials, he adds, plan to use QuickBird for two other airport projects in the near future. "The imagery is now being recognized as an efficient tool for managing airport facilities, especially those experiencing rapid growth and expansion."
The satellite's 61-centimeter resolution panchromatic sensor and 2.5-meter multispectral (4-band) sensor are based on a "pushbroom" scanning array, which sweeps over its target area rather than concentrating on a specific point on the Earth's surface, as do "staring" and "spinning" arrays. The pushbroom sensor targets a point on the ground, then moves across a specified area, collecting continuous images many times larger than the sensor projection itself. This results in efficient sensor collection and requires less mosaicing to large area-images.
The satellite can acquire 16.5-by-16.5-meter multispectral and panchromatic images over the same area in one pass, and can acquire data at an 11-bit pixel depth. As an "agile bus", the entire satellite can tip and tilt to focus the sensors on requested areas for acquisition.
The orthorectification process corrects for distortions from viewing geometry (including terrain effects) as well as distortions in the sensor. The correction process involves first calculating for viewing geometry, then combining that with corrections for sensor geometry.
DigitalGlobe officials say they plan to launch a constellation of four M5 satellites that will collect five-meter resolution multispectral images of the Earth by the end of 2007. Company leaders say covering a wide area on such a frequent basis will enable them to provide images of the Earth's entire land surface every four days.
Investors in the privately owned enterprise include ITT Industries Inc., MorganStanleyDeanWitter, Ball Aerospace & Technologies Corp., Hitachi Ltd., and Telespazio S.p.A./Eurimage Investment.
While its open-skies policy makes images of any location on the planet available to the commercial market, DigitalGlobe says in the case of a threat to national security, it will comply with any U.S. government regulations and restrict access to imagery as required.
