September 3, 2008 By Tom Patterson
team. They all worked comfortably within the confines of the heated vehicle during the 12- to 16-hour shifts. This arrangement made for a smooth workflow in which SAR teams would bring their GPS receivers, used to document their area searched, to the Mobile Mapping Unit at the end of the shift.
While the teams searched their assigned areas, their progress was recorded on handheld GPS receivers. Waypoints depicting the coordinates of any clues found, such as tracks, discarded food wrappers or items of clothing, were also recorded into the devices. At the end of the shift, these track logs were downloaded and converted into shapefile format by the GPS technical specialist using Maptech's Terrain Navigator Pro software.
Maptech is an ESRI business partner, and its mapping program is popular with many SAR teams and fire departments. It easily displayed and exported GPS track logs collected by the teams and converted them into a single shapefile. With ESRI's ArcInfo software, staff could then use the single shapefile to create a comprehensive search history and incident action plan maps. As the last team went through the debriefing process, it took little time to display an overall picture of the entire day's activities, which were also overlaid with previous operational periods. Search managers could tell at a glance where to deploy resources for the next day. GPS data was also downloaded from the AeroComputers Tactical Mapping System from each of the helicopters and displayed in ArcGIS. These aerial layers could be easily combined with the ground team's data to enhance the decisions being made for the next operational period. For example, the information helped determine which areas were adequately searched and which ones needed to be revisited.
"Additionally having a full map set with GPS track logs to put into the case file helps us direct future operations in the area and to document a higher standard of care," Lane said.
GIS was also used to attempt to pinpoint potential areas where Christy might have made his last 911 call. The California Highway Patrol's 911-dispatch center provided the coordinates of that location. The accuracy of that point was plus or minus 550 meters, and officials were convinced that it went through the Strawberry Peak cell site, 10.8 air miles away to the east in Rim Forest.
ESRI's ArcGIS Spatial Analyst extension was used to perform a viewshed analysis of all the areas within a 1,000-meter circumference surrounding the location where Christy placed the call that had a line of sight to the Strawberry Peak cell tower. Searchers made cellular phone calls from random locations in the zone identified as the one from which Christy called for help. The calls made within the shaded areas were able to connect with the 911 dispatcher through Strawberry Peak; those outside the orange polygons on the map either couldn't connect or else connected through cell towers on the Victorville side of the mountain. This map, along with the search history maps, was used to brief Christy's family and help incident commanders make an informed decision to scale back the operation on the afternoon of Jan. 13.
However, the search remained active. On April 4 - three months to the day since he went missing - the Rim of the World Search and Rescue Team found Christy's body northeast of Green Valley Lake, less than 1.5 miles from his home.
"On trails he had traveled approximately 3.5 miles," said the SBSD's Lane. "He sheltered between a rock and a large tree. It appears there may have been some branches on the rocks above him that he may have used to protect himself."
Christy was located in a rock outcropping in an area identified in the viewshed analysis as having line of sight to the Strawberry Peak cell tower.
You may use or reference this story with attribution and a link to