City looks to satellites for mapping

Some day, maybe every city will have its own satellite. At least several U.S. companies think so. They are rushing to launch satellites that will allow them to compete for the projected $3 billion initial market for high detail images previously available only to the world’s intelligence community.

But for Cupertino, Calif., that day is here. In Cupertino, Public Works Director Burt Viskovich and GIS Database Coordinator Tim Stone are awaiting the planned launches this year of private enterprise satellites carrying sophisticated imaging equipment for recording earth features. The pair sees satellite imagery as superior to digitized paper maps — the current format for the city’s maps — for civil engineering, planning, presentation and city management projects. The two anticipate that, by the end of the century, the city’s entire map database will be digital orthophotos and space images.

Cupertino is in the pro-cess of evaluating several products and services including the Carterra San Francisco Series digital information from Thornton, Colo.-based Space Imaging EOSAT, which provides one-meter pan-chromatic, four-meter multispectral and one-meter color-enhanced imagery. Although the data was created from aerial source material collected by Oakland-based Hammon, Jensen, Wallen & Associates, it is said to accurately represent the characteristics of future satellite imagery.

“We are hoping to be able to locate sites based on the land form to aid in distributing information across our organization and also to the public,” Viskovich says.

The first priority is to build a GIS file management system that will allow department personnel to query the database directly from the imagery. “We’ve already layered our parcel data on top of the imagery, and we’re viewing it using ARC View (ESRI, Redlands, Calif.),” Stone says. “By clicking on the imagery, you can call up a parcel and all of its attribute information.”

Satellite imagery creates a substantial niche between the 15-meter resolution satellite pictures available today and the more expensive high-accuracy sub-meter digital orthophotos rendered by conventional aircraft. Consistency, predictability and precise coverage are other advantages. Winds that keep aircraft on the ground are no obstacle to satellites. And because of their high speed, the sun-target-sensor relationship provides seamless mosaics of large or small areas even if the images are taken days or weeks apart.

The satellites’ side-, frontward- and backward-looking ability of about 45 degrees off nadir (vertical track) provides for a variety of stereo options that are more difficult to achieve with airborne cameras.

Still, the greatest advantage, according to Viskovich, will be the money saved by updating the imagery without having to re-fly the territory. The satellites will be positioned to fly from pole to pole in a sun-synchronous orbit at about 16,000 miles per hour, returning to the same areas every one to three days. This will enable city users to monitor ongoing construction projects and land development; track pollution and polluters; and monitor a variety of dynamic events on the face of the earth.

The pixels of both aircraft and satellite images can be blended to form a single map sheet.

One-meter space images provide exceptionally detailed ex-tended overall coverage, while aircraft cameras can concentrate on extremely fine detail for selected areas within the frame.

Satellites enable coverage of small areas of interest on any given day. “We are looking forward to being able to select small sections of data from the space company’s inventory and purchasing updates based upon what we need for specific projects,” Viskovich says. Earthquake- and mudslide-prone California can monitor the earth’s subtle and dramatic changes using “snapshots” of small areas, he predicts.

Cities will also be able to choose between receiving the digital images in panchromatic format for engineering work or blended with multispectral images to observe environmental change.

“We are preparing for [space imagery] by selecting a browser to be able to link with the Internet to exchange a lot of information with other utility companies and agencies,” Viskovich says.

Web-based systems architectures for creating, viewing and transferring map data are expected to be deployed throughout city departments to maximize the use of imagery for applications including cadastral mapping, redistricting, work order management, planning, dispatch and police and fire operations.

This article was written by James Black, a Denver-based freelance writer specializing in information technology issues.