Big Picture

Satellite images help Prescott, Ariz., assess fire damage and prepare for the next disaster.

by / December 20, 2002
Forest fires blazing through Arizona in May 2002 destroyed thousands of acres of land. Given the warm, dry, windy conditions typical of southwestern states, cities in this region accept that once started, fires will spread quickly and easily. It is critical that emergency response officials track the progress of these fires. Using satellite images, which illustrate the layout of the land and show everything -- roads, fire hydrants, vegetation, reservoirs -- that firefighters navigate on their way through a fire. They can also predict the path of a fire before it strikes, protecting residents from a future inferno.

In the early afternoon of May 15, a fire broke out near Indian Campground in the Prescott National Forest, approximately seven miles south of the city of Prescott. The temperature was in the 90s, with wind speeds reaching 25 mph. Fueled by extremely dry tree and ground cover, the fire quickly expanded and spread into the forest; within hours, the blaze came within three miles of the city. Although the fire was contained just two days later, it wasn't too early to prepare for the next inevitable attack.

Prescott's GIS department has been leading the city's research into reliable mapping and planning technologies. During the Indian fire, the GIS team supplied ground crews with an ability to visualize the terrain and road networks using two-year-old satellite imagery of the Prescott area. But the team recognized a need for more recent, higher resolution imagery to accurately assess post-fire conditions and support fire prevention efforts. Therefore, the city selected DigitalGlobe's half-meter resolution QuickBird images -- which offered a current view of the charred landscape and provided the detail and accuracy needed to thoroughly map the area.

The satellite images offer an accurate "big-picture look" at the local geography, according to Darrell Willis, Prescott's fire chief. "Much of the time, firefighters have to rely on hand-drawn maps. Unfortunately, hand-drawn maps just don't offer the perspective needed to assess the risks and resources needed to fight a fire," Willis said. "Detailed maps are especially important when we turn the management of a fire over to a type 1 national team. They're not as familiar with the area as we are and need to be aware of what's been evacuated, what's threatened and where the homes are."

Willis said the image detail allows his team to count at-risk structures and determine how many engines should be released to protect homes during a blaze. "We have a formula for calculating how many resources we need -- if we underestimate the number of homes in the fire's path, we won't send the appropriate resources. With the high-resolution images from space, we're ahead of the ball game, and firefighters can hit the ground running."

As a post-fire analysis tool, the QuickBird digital satellite images were essential for evaluating burn patterns, estimating the fire's speed based on wind conditions and determining possible ignition points. The extent of damage included approximately 1,300 acres of federal forestlands and 30 acres of private lands. Because the half-meter resolution of these images shows detail down to the house level, they illustrate precise damage to structures. The images indicated that only four residences were burned, one residence was partly damaged and one out-building was completely destroyed.

Although aerial imagery could have captured this information, satellite imagery made more sense because of its wide-area coverage and digital qualities. Airplanes are limited in their ability to capture images of a large area, so multiple images must be collected then pieced together later. In many cases, aerial imagery is collected in analog form. To make it useful later -- when detecting change or enabling quick sharing with other government offices -- analog imagery must be digitized. This often is time consuming and expensive. Digital satellite imagery can be used and shared immediately.

Looking forward, the satellite image maps will be valuable for preparing the city and its residents for the next fire. Images detailing vegetation conditions, road networks and population centers help city agencies and relief organizations understand the area's rapidly changing conditions. Information about vegetation health and drought stress allows officials to determine which areas are most prone to fire danger, thus predicting the likely path of a fire and developing strategies to contain it. The city can prepare high-risk residents by warning them about fire dangers and supplying them with maps showing evacuation routes. If roads are closed, residents know their safest emergency escape in advance.

Prescott City Manager Larry Asaro cites public safety as the biggest driver for routine mapping. "For fires and other emergency situations, we need fast access to accurate information about the entire area," he said. "For example, by knowing where all the new roads are, and even the roads that are hidden from normal ground view, fire-fighting personnel will see all the possible approaches to a fire. The timeliness and quality of the new satellite images are critical in these situations.

"Flooding is always a concern after a fire because the vegetation has been destroyed, and there's a greater risk of water runoff and erosion," Asaro continued. "The satellite imagery can help us estimate the amount and location of erosion risks."

Satellite images provide a terrific visual depiction of the terrain, vegetation and urbanization. However, it is their integration with GIS that gives them versatility. Used in GIS and overlain with data showing street centerlines, property boundaries, building footprints, and gas and electric lines, the imagery takes on a life of its own and becomes a planning utility for numerous purposes.

From a data-sharing perspective, Asaro said satellite imagery helps address the need for accurate data in a GIS. "Our GIS is shared by different departments that rely on up-to-date parcel maps. These maps are the cornerstone of our data pool; underneath the maps are data layers containing information about vegetation, traffic, water, street centerlines, road surface quality, etc. The satellite imagery ensures that our underlying data is as accurate as possible." When new images are captured, their digital nature allows easy change detection and quick database updates.

For the city of Prescott, the Indian fire was a wake-up call; many areas are susceptible to disastrous fire damage. The use of image-based GIS operations gives firefighting personnel an advantage by providing updated satellite imagery for ongoing support of firefighting and prevention efforts.

Dale Anderson is GIS coordinator for the city of Prescott, Ariz.
Dale Anderson Contributing Writer