Police say they do not think the confusion hampered the rescue effort, as emergency responders on jet skis reached the correct site within six minutes of the initial calls, shortly before 7 p.m. More than a dozen swimmers were rescued. The body of Corinthian Hammond was found four days later near the bridge joining Ocean City and Longport.
Few people were in the water that evening, regular lifeguard patrols having ended for the day, said Capt. Steven K. Ang, an Ocean City police spokesman. So, once rescuers were in the water, they "could easily scan the horizon and say, 'There's nobody here,' " he said, "then look to your right and say, 'Oh, there's people there,' [and] pick up right away where there's a problem."
That is not always the case, though, and as more and more 911 calls are being made from mobile phones, the location problem has become increasingly apparent. Landline calls automatically have the location attached to them, but according to the Federal Communications Commission, 38 percent of U.S. households no longer have landlines.
Technology gaps have concerned dispatchers and police departments nationwide, prompting an FCC workshop on the issue held in November.
Emergency-response agencies across the country, including Delaware County's Department of Emergency Services, submitted data to the FCC indicating that dispatchers often do not get electronic location estimates for wireless 911 calls. Delaware County's data showed that in the long term, it was missing in two-thirds of cases.
"If you don't know where the guy is, you can't help him," said Edwin Truitt, Delaware County Emergency Services director.
Mobile-phone carriers counter that in many cases where location information is missing, it is indeed being transmitted to a central server, but the data can take up to 30 seconds to arrive on dispatchers' screens. When that happens, dispatchers should resubmit a request for the location, according to CTIA, a wireless industry group in Washington.
Carriers rely on various technologies to determine location, said Trey Forgety, director of government affairs for the National Emergency Number Association, a nonprofit based in Alexandria, Va., that represents 911 call centers.
One method, considered the most accurate, relies on satellites that are part of the nation's global positioning system (GPS), Forgety said. It works best outside, requiring a direct line of sight between the user and multiple satellites, said Kapil Dandekar, a Drexel University professor of electrical and computer engineering.
When satellite technology doesn't deliver, carriers have various fallbacks. Most use signals sent between handsets and cellular towers, making measurements such as direction, angle, and elapsed time of transmission, Forgety and Dandekar said. Most tend to work better outside as well.
The FCC requires carriers to validate their technology in outdoor test conditions, but not real-world situations. For methods that rely on technology embedded in the mobile handset, the system must be accurate within 50 meters in two-thirds of test cases. A location within 150 meters must be achieved 95 percent of the time.
In the Ocean City drowning, the four callers were outside. In the two instances where a location was transmitted to the dispatcher's computer screen, it was spot-on, within a few feet of Ninth Street and the boardwalk.
In each of the other two cases, the system revealed only the location of the cell tower from which the call was transmitted. One of those callers actually knew the location of the incident and relayed it verbally. In the other, the audio was unintelligible.
Even when the automatic location system works, it comes in the form of latitude and longitude coordinates in Ocean City, not a readily accessible street location, Ang said. "If I had a dispatcher who was taking a stressful call, he would have to distract himself from talking to the caller to go to a different screen and Google these two numbers."
Some 911 call centers have software that automatically converts latitude and longitude to a street address, such as in Delaware County, said Charles Brooks, chief of operations for the Emergency Services Department.
Before long, the technology will be held to a higher standard. In February, the FCC proposed rule changes that would require carriers to provide locations for 911 calls made indoors, including a vertical component that would allow emergency personnel to pinpoint a floor of a building.
Dandekar, the Drexel engineer, said there were several ways this might be achieved. Among them: Make use of location data from WiFi networks or from small, low-power cellular stations that are situated indoors.
Four people called 911 the evening of June 29 to report swimmers in distress in Ocean City, N.J. At least two did not know where they were: Ninth Street and the boardwalk. An automated location system - dependent on a series of electronic handshakes among the cell carriers, a central server, and police dispatch - provided inconsistent results.
- Tom Avril
Synopses of the calls
6:44:26: Caller is unsure of location, but, after questioning by the dispatcher, says incident might be at 14th Street. Automated system indicates call originated near Ninth Street and the boardwalk, the actual location. (Carrier is Cricket Wireless.)
6:44:59: Audio from another caller is unintelligible. The automated system locates only the nearest cell tower, at least a half-mile away. (AT&T Mobility.)
6:46:37: Caller doesn't know location. Automated system pinpoints it correctly. (Sprint.)
6:46:45: Caller states correct location. Automated system locates a cell tower only. (T-Mobile.)
SOURCES: Ocean City Police Department data and audio recordings.