Denver wastewater uses DigitalGlobe impervious surface map products to improve efficiency for storm water billing purposes

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Denver wastewater uses DigitalGlobe impervious surface map products to improve efficiency for storm water billing purposes


LONGMONT, Colo., May 24, 2004 -- DigitalGlobe®, provider of resolution commercial satellite imagery and geospatial information products, announced that Denver's Wastewater Management Division (WMD) has evaluated QuickBird imagery and DigitalGlobe's impervious surface map products in order to streamline WMD's storm water billing operation.

In a study conducted by WMD and DigitalGlobe, the use of two-foot resolution multispectral QuickBird satellite imagery processed using superior classification techniques to produce an impervious surface map resulted in a rate of revenue generation nearly four times greater than that produced using traditional mapping methods.

WMD's customer service group is responsible for billing all property owners in the City and County of Denver for sanitary sewer use and storm water drainage collection. Storm water runoff is a major contributor of pollution to reservoirs, lakes, streams and other surface waters. The storm water drainage bill is calculated by mapping the impervious areas -- or surfaces that water does not penetrate, such as concrete and asphalt - contained within a parcel. Once the amount of impervious area contained within a parcel
is determined, that property's billing rate is calculated. While many cities that bill for storm water management do so by charging property owners based on average parcel size and landuse, Denver's WMD bills property owners based on actual property size and total impervious surface area contained within the property. Essentially, property owners are billed according to their contribution to storm water runoff.

To help maximize the efficiency of its billing operation, WMD initiated a pilot project in May 2003 to determine the effectiveness of using high-resolution multispectral (blue, green, red, near infrared) satellite imagery for mapping impervious surfaces in five Denver neighborhoods, including three residential, one commercial, and one industrial neighborhood. For the project, DigitalGlobe donated QuickBird imagery collected in April 2003.

WMD found that the QuickBird satellite imagery offers significant benefits in terms of cost and delivery time, allowing for quicker mapping, assessment, billing, and revenue generation at a lower cost to WMD.

"WMD is accountable for accurately billing customers," said Jeff Blossom, WMD's GIS photogrammetry administrator. "Outdated images are our biggest limitation when it comes to efficiently mapping impervious surfaces and maintaining our storm water billing utility databases. Integrating QuickBird imagery into the city's GIS presents an opportunity to streamline our storm water billing process and keep our databases current," he said.

WMD has also found that utilizing QuickBird imagery provides a quicker, more consistent and precise method of identifying properties where a change of impervious area has occurred, and flagging the area for updates.

For instance, if a customer replaces a large amount of concrete on his property with grass or other pervious material, the impervious surface area decreases in size, qualifying him for a lower billing rate. WMD's current method for identifying changed properties is to do a visual comparison of existing impervious areas and recently collected imagery -- a time-consuming, manual, often tedious process. DigitalGlobe's automated algorithm identifies changed properties throughout the entire city in just a few minutes.

According to Blossom, the two-foot resolution QuickBird data costs roughly one-tenth the amount of six-inch resolution aerial orthophotos. DigitalGlobe delivered the imagery within two weeks, compared to the four to six months typically required for traditional aerial photography. WMD has used aerial orthophotos for Denver's impervious surface mapping since 1988. WMD will continue to use aerial data due to its high resolution, but Blossom hopes to supplement it with new QuickBird imagery at least every year to keep the WMD databases up to date.

"With the current trend of rapid expansion and change occurring in the City and County of Denver, acquiring lower cost QuickBird imagery at more frequent intervals on a city-wide scale could also benefit many city departments that rely on updated feature mapping," said Blossom. He added that the most recent aerial data collection took place in 2002, and, "a lot has changed in Denver since then."

According to Blossom, several other departments in the City and County of Denver could possibly benefit from a collaborative, multi-agency acquisition of QuickBird imagery, including the departments of Environmental Health, Development Engineering Services, Infrastructure Planning & Programming, Parks & Recreation, Transportation, Engineering, Fire, Police, Emergency Services, and Central Planning.

About DigitalGlobe

DigitalGlobe is an Earth imagery and information company in Longmont, Colo., USA. With the 2001 launch of its QuickBird satellite, DigitalGlobe has established a market leadership position. The company offers the world's highest resolution commercial satellite imagery, the largest image size and the greatest on-board storage capacity of any satellite imagery provider. DigitalGlobe's ImageLibrary houses the most comprehensive,
up-to-date images available.

Since January 2002, QuickBird has collected and stored in its ImageLibrary more than 315,000 scenes of imagery covering more than 95 million square kilometers of the Earth, and collects an additional one million square kilometers each week. The competition has no plans to launch a comparable commercial satellite until at least 2008. The superior technical capabilities of DigitalGlobe's WorldView system, scheduled for launch no later than 2006, will lead the industry into the next generation of commercial imaging. DigitalGlobe distinguishes itself through its commitment to excellent customer service, relationships with business partners and open-systems philosophy. More information can be found at

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