Eyes for a Sharper Image
SATELLITE-FURNISHED IMAGERY UPGRADES ARE ON THE HORIZON WITH THE INTRODUCTION OF A NEW GENERATION OF CAMERAS.
A new generation of commercial satellitebased camera systems expected to be operational in the first half of 2007 will provide electro-optical imagery in increased quantities, and with higher resolution and improved geolocation accuracy.
The Worldview-1 and GeoEye-1 satellites are being built as part of National Geospatial-Intelligence Agency (NGA)-awarded NextView contracts to DigitalGlobe and Orbimage, respectively.
As the original winner of the NextView contract, DigitalGlobe will launch the WorldView 1 satellite in mid-2007. DigitalGlobe currently owns and operates Quickbird, the world’s highest- resolution commercial satellite, which captures images at 0.6-meter resolution.
Ball Aerospace is the manufacturer of the WorldView satellite system. ITT built the sensors for this satellite and delivered the Worldview 1 sensor this past summer.
In January 2006, Orbimage acquired its rival, Space Imaging. The partnership, renamed GeoEye, is the world’s largest satellite imagery company. The GeoEye-1 will be launched next spring. ITT is designing, building, testing and delivering the camera payload for GeoEye-1.
“The camera is the eye of the imaging satellite,” explained Kyle Schmackpfeffer, GeoEye-1 camera payload program manager for ITT. Spacebased cameras provided by ITT and its other industry counterparts are similar in principle to a digital camera, except that satellite-borne camera systems are much larger—three meters tall in the case of the GeoEye-1 satellite.
The basic parts of a satellite camera payload are the telescope, which creates the image, and the digital electronics that record and process the image.
The telescope is designed to give a perfect (diffraction limited) image to an electronic focal plane that records, processes and prepares the image for storage on the spacecraft and transmission back to earth.
“We use three mirrors to image and focus the light, and two additional mirrors to direct the image to the location of the focal plane,” said Schmackpfeffer. “It is important that the mirrors remain perfectly co-aligned to one another, so we use specially formulated, extremely stable, lightweight composite structures to hold and maintain the alignment of the optics.”
The current generation of commercial satellites has mirrors that range from 0.5 m. to about 0.8 m. in diameter. ITT’s primary mirror for GeoEye is 1.1 m. in diameter.
FOCAL PLANE
ITT’s focal plane arrays capture the images and convert them to digitized signals. “These signals are processed by the supporting electronics and sent to the onboard data recorder for transmission to the ground,” said Schmackpfeffer.
The focal plane consists of an array of 8-micron panchromatic detectors for black and white imaging, and four arrays of 32- micron multispectral detectors for color imaging in blue, green, red and near-infrared. ITT has included an outer barrel and door assembly to help protect the telescope and maintain its thermal environment.
The current breed of in-orbit camera systems for commercial applications has an approximate resolution of 0.6 m. to 1 m.
This present capability is placed in context by one industry source. “From a military perspective, users can identify armor and support vehicles, for example distinguishing between tanks, armored personnel carriers and self-propelled artillery, and can measure the length, width and barrel lengths of artillery,” said Stephen Wood, director of national security programs for DigitalGlobe.
“From a civilian or commercial perspective, users can distinguish between cars and small utility vehicles and vans. Fan blades on cooling units associated with buildings can be identified, and people can be observed in many but not all situations. All of these types of characteristics are only possible using sub-meter high-resolution imagery,” concluded Wood.
The GeoEye-1 sensor will collect panachromatic imagery at a resolution of 0.41 m. and multispectral imagery at 1.65 m at nadir. WorldView 1 will supply 0.45 m. panachromatic imagery at nadir.
Technology is only one factor in the quest to achieve improved resolution capabilities, developers make clear.
“It is not so much a technology issue as a licensing and business case. The higher the resolution, the larger the telescope and satellite as well as launch vehicle,” said Chuck Herring, director of media relations for DigitalGlobe. “Generally, the footprint size—the amount of imagery that can be collected—can be reduced as well. Due to current U.S. licensing restrictions, U.S. satellite imagery companies can only sell imagery better than 0.5 m. to the U.S. government.
“If you have to spend more to collect less land mass and can only provide the full resolution to one customer, the business case does not necessarily fit,” Herring suggested.
“We planned 0.5 m. for WorldView 1, but with WorldView 2, we have the flexibility built in. We can provide 0.5 m. imagery at an 800 km. orbit with even more capacity, 950,000 sq. km. a day, or lower the orbit to 450 km. and collect 0.25 m. resolution. We can change the orbit right up until launch, which is currently planned for late 2008,” added Herring.
INCREASING IMAGERY
The consumers of satellite imagery have yet another requirement—collecting ever-increasing amounts of imagery in a period of time.
“GeoEye-1 has a very large swath and a very high scan rate so that we can collect very large areas when compared to our current system,” said Dave Kenyon, senior director, NextView Space Segment, GeoEye.
The nominal swath width of the Geo- Eye-1 is planned to be 15.2 km. at nadir, during its 12 to 13 orbits per day, from an altitude of 684 km. The legacy Orbview-3 satellite has a swath of 8 km.
The GeoEye-1 will collect imagery over “several hundred thousand square kilometers per day,” said Kenyon. The satellite’s fact sheet notes the system will be able to collect up to 350,000 sq. km. of multi-spectral and 700,000 sq. km. of panachromatic imagery per day.
By way of comparison, the land area of Afghanistan is 647,500 sq. km., while the land and contiguous water area of Iraq is 437,072 sq. km.
For its part, WorldView 1 will have an even larger swath width of 17.2 km. at nadir and collect 750,000 sq. km. per day from an altitude of 496 km. during its 15 orbits per day.
“The satellite’s agility, or the ability to point at targets, will be unmatched,” remarked Herring. “Worldview 1 will be the first and only commercial imaging satellite to fly with control moment gyros that provide five to 10 times more satellite agility than standard gyros,” added Herring.
Geolocation is the capability to take an image of the ground and know exactly what that location is in terms of latitude, longitude or other measure, within a very small number of meters. One practical application would establish the intersection of two roads from a pixel within several meters accuracy.
GeoEye-1 will be able to precisely locate an object within 3 meters of its true location on the surface of the Earth.
With ground control points, WorldView 1’s geolocation accuracy is 2 m., and 5.8 m. to 7.6 m. without the resource, said DigitalGlobe’s Herring.
While the next generation of satellites brings the expectation of more accurate, more bountiful and higher-resolution imagery, opportunities remain on the community’s horizon.
Several challenges continue to face the industry-government team even as more capable and additional camera systems become operational.
One of the NGA’s greatest challenges is in the application of common standards for imagery and metadata.
“As we process imagery from a variety of and growing number of sources, the ability to ‘stitch’ these together to develop an integrated product or monitor an area over time with imagery from different sources becomes more challenging,” said Doug McGovern, chief of commercial solutions for NGA.
“This agency requires the bulk of imagery purchased from the commercial sector to be National Imagery Transmission Format- compliant. While this may be overkill for some applications and users, the adoption of more rigorous standards internationally and in the commercial airborne sectors should ultimately help those building GIS applications and the user,” added McGovern.
Bandwidth availability is often an Achilles heel for planners of terrestrial operations. The capability is also viewed with increased interest by those supporting satellite- based missions—as more capable satellites will produce ever-increasing amounts of on-board imagery.
One representative increase will occur when the capacity of the legacy DigitalGlobe QuickBird with 128 gigabits will expand to 2,199 gigabits on the company’s next-generation WorldView 1.
“Getting the imagery on the ground, processed and to the end user in a timely manner is a challenge. There is only so much bandwidth available in the downlink from the satellite to the ground. That is a constraint and a challenge,” observed GeoEye’s Kenyon.
The distribution of imagery is also on NGA’s radar screen. “Large image files and ‘small pipes’ of communications bandwidth is the norm that generally frustrates users trying to download imagery,” pointed out McGovern, adding that enhancements in lossless data compression and image streaming technologies would be of great interest. ♦
