Differential GPS and California's Disasters

Oct. 1995 Level of Government: State Function: Disaster Management Problem/situation: When earthquakes or other disasters strike, it's difficult to give a location for features without addresses. Solution: Differential GPS pinpoints feature locations. Jurisdiction: California Governor's Office of Emergency Services. Vendors: Trimble Navigation, Differential Corrections Inc., ESRI. Contact: Terrie Monaghan, public assistance program manager. 818/431-3290. monaghant@caoes.geis.com

By Brian Miller Features Editor When a natural disaster strikes, information is the lifeblood of relief and recovery efforts. But with electricity out, bridges washed away or shaken, and general chaos among victims, disaster managers have had difficulty pinpointing the precise location of various features and occurrences. But in California, which has a reputation for periodic man-made and natural disasters, crews have begun using differential global positioning system (DGPS) to record the precise location of unsafe bridges, buildings and intersections to help coordinate immediate disaster response as well as keep a record for future analysis. The California Governor's Office of Emergency Services (OES), which bought about 100 Trimble Scoutmaster GPS receivers, issued units to field workers after the January 1994 Northridge earthquake. OES response personnel carry a GPS unit about the size of a cellular telephone and have a differential unit the size of a pager cabled to the GPS unit. Differential services were provided by Differential Corrections Inc. of Cupertino, Calif., after the Northridge quake. In Northridge, the exact location of cracked bridges, broken gas or water lines and unsteady buildings was recorded. The data was later loaded into a geographic information system (GIS) for spatial analysis and recovery planning. OES is using Arc./Info, Arc/View from ESRI, based in Redlands, Calif.

INADEQUATE ADDRESSES A key advantage to using DGPS is that the locations are determined with latitude, longitude and elevation. This is important because addresses have been the main method for recording geographic information. The problem with this is that features such as bridges don't have addresses, making it difficult for crews to communicate precise locations. Sometimes addresses are impossible to use even in residential areas hit by a disaster. For example, after Hurricane Andrew ripped through Florida in 1992, recording damage location was made difficult because street signs in many areas had been blown away. Before GPS and GIS, disaster recovery personnel would use physical maps and make guesses as to the location of some of the damage areas. Workers would use paper and text descriptions to indicate what was damaged and its location. This data was then combined with other reports and cross referenced by hand. This process made for a time-consuming chore when time was of the essence. With the data loaded onto a GIS from DGPS, not only is location data more accurate, but it is easier to read than the old paper maps and text. "We use it for visualizing damaged areas," said Terrie Monaghan, OES program manager for public assistance. "And if we don't know where it is at, we can look at a map, click on that point, and know exactly where and what it is." Monaghan said that the system can also be used in cooperation with local authorities using GIS. If the county has latitude and longitude for all its bridges, for example, data collection from damaged structures can be plugged into the system and shown on a GIS map.

TRIAL AND ERROR The new system is much easier and more mobile than the "old" method used in post-disaster assessment by OES personnel. Laptop computers were used by crews during the Los Angeles riots in 1992, and location data had to be entered in text form. OES also had state Forestry Department aircraft fly over the strife-ridden area to take photographs in an attempt to determine what was damaged and where. "This proved to not be the most effective way," Monaghan said. "Then we drove the streets during the riots, and would stop at intersections and try to