by Gary Allen
Boys and girls lying in the grass under a star-filled sky 35 years ago couldn't imagine the satellites they watched would eventually help a dispatcher guide a police car to its next assignment.
But that technology arrived at the Schaumberg, Ill. Police Department in February 1992 when 40 patrol cars rolled out with an automatic vehicle location (AVL) system based on Global Positioning System (GPS) satellites. Now, dispatchers know exactly where the cars are at every moment.
Right now, Schaumberg dispatchers are using the AVL system visually to determine what units are closest. They study a color monitor that displays units and incidents overlaid on a map of the city. But within a year, more advanced programming code will automatically display the closest unit when the dispatcher requests a recommendation.
"That's where the technology is going. It's not here yet. We still have to look at a map," says Lt. Tom Ostermann, who handles Schaumberg PD's technical services. "We went from the stone ages to the future overnight, all in one major step."
Schaumberg, a 26-square-mile suburb of Chicago, spent $3.5 million to upgrade their CAD software, convert to 800 MHz trunked radio and mobile data terminals (MDTs), and build a new communications center.
The CAD software was supplied by Integrated Computer Concepts, Inc. (ICC), the MDTs and radio system by Motorola, and the GPS receivers by Trimble Navigation.
Ostermann says the commonly used police beats don't account for adjacent beat officers when making recommendations. With AVL and GPS, the dispatchers can make a more informed decision on which unit to send.
As for accuracy, Ostermann says they have never noticed a case where the map showed a patrol car far from its actual position. "I'd say they're within 50 feet of that intersection without a problem."
Besides providing real-time tracking of patrol cars, Ostermann says the system can store vehicle locations and play them back at higher speed for analysis. The screen display shows the vehicle location and the computed speed of the vehicle between two points.
Ostermann says AVL is particularly helpful when dispatching the department's Community Service Officers, who handle non-criminal matters. "You can just ship him the next closest call because you know where he's at because you're looking at a map."
Despite the possible "big brother" aspects of AVL, police officers didn't complain, says Ostermann. He gave the officers two reasons for using AVL--"One, is to get the best response that we can to the emergency calls that are out there, and two, is their safety."
The officers were convinced, but they tested the system capabilities. "Did they try to find out what can defeat it? Yes," says Ostermann. The police officer officers' inherent curiosity made them try all sorts of tactics, to see how the AVL system would respond.
Despite the high-tech nature of the AVL and GPS electronics, the system isn't complicated to operate or maintain. "It's all self-enclosed within that little receiver," Ostermann says. The antenna, about the size of an upside-down soup bowl, mounts to the top of the car or trunk and the receiver is a compact unit mounted in the trunk.
Beyond all the hoopla of technology, what's the system do for dispatchers? "It's unbelievable," says Ostermann. "When you're in a dispatch center, you've got a blanket over you. It's like lifting that blanket."
But more than just providing the dispatchers with a tool to help speed an emergency response, Ostermann sees a more personal benefit. "When the dispatchers know where those cars are, I sense a lessening of anxiety."
"I think anxiety plays a part in dispatching a lot. This is just one level of anxiety that can be removed from that job," Ostermann says.
GPS Technology
The Global Positioning System (GPS) was developed by the Department of Defense (DOD) for $8.5 billion as a way to absolutely pinpoint locations anywhere on earth, in three-dimensional space. It improves upon other navigational systems designed primarily for mariners, such as Loran-C and Omega.
The 19th satellite was launched into orbit 10,898 miles above earth early this year, finally providing 24-hour coverage to the entire globe and making them marketable to public safety agencies. Each of the satellites, controlled by a ground station in Colorado Springs, is expected to stay in orbit 7-1/2 years.
Simply put, GPS satellites generate very accurate time signals and continuously broadcast them over a line-of-sight path in the 1200 and 1500 MHz band. GPS receivers decode the time signal, perform some sophisticated math, and derive the receiver's location.
If you venture beyond this fundamental explanation, you get caught up in ephemeris, orbits, differential processing and trigonometry. But there are some GPS issues that are essential to understand.
Accuracy is a major issue for public safety agencies, but like most technology, it's a difficult one to explain.
"It's not a simple answer," says John Wenzel, Trimble Navigation's product manager for public safety. He's not trying to hedge, hoping to make a sale. There are lots of considerations here, not the least of which is the Department of Defense.
When the system was first conceived, two signals were provided--one coded signal for the military (P-code) and one for civilians (C/A signal). The two are broadcast on different frequencies but provide similar accuracy.
But the system is so accurate that the DOD degrades the civilian signal so unfriendly nations can't use the system for strategic purposes--so-called "selective availability" (S/A). The degradation is selectively turned off and on, and it randomly varies the accuracy of a particular satellite. This results in an average accuracy of 100 meters when S/A is turned on.
You're not supposed to know when S/A is turned on, although sources say it's easy to tell. So you must always assume a lower accuracy, even though the signals you're receiving may not be degraded at that particular moment.
Ironically, S/A wasn't used during the 1990 Gulf conflict because not enough of the military-code receivers were available to the troops. Many were equipped with civilian models that could only receive the C/A signal.
With S/A turned off, Wenzel says civilian GPS typically has an accuracy of about 20 meters anywhere in the world. However, there's a trick to improve even this accuracy--differential processing.
Differential is simply a way of taking GPS readings from a known location, then applying any error readings from the satellite as corrections to readings from other sites. The Coast Guard is already building a network of six coastline GPS differential stations that can be used by anyone within 1000 kilometers.
"By adding the differential capability, even on the degraded military signal, we still can get the accuracy down to below 10 meters, so it averages about 5 meters," Wenzel says. For Trimble's typical fleet customers with several hundred vehicles, the added cost of the differential feature is insignificant.
Want even more accuracy? If you're surveying and can take a fix every second or so, accuracy comes down to two meters. And, using a properly equipped GPS receiver, and taking fixes every second over 15 minutes, you can reduce accuracy to a centimeter--about one-third of an inch.
"It depends upon what your application is and what receiver you're using," Wenzel says. Trimble Navigation's newest version of GPS includes dead reckoning, so an interruption of the satellite signal doesn't stop the flow of location information back to the comm center.
The last word on accuracy has to be a comparison with other available technologies. "Comparing it with any other technology that's ever been available, it's an order of magnitude better," Wenzel says.
For example, Loran-C uses 90-110 KHz signals from several of 94 stations scattered around the globe to give an accuracy of about 500 meters. Omega, another radio-based technology, broadcasts near 10 KHz and has somewhat better accuracy, but you have to know your starting point location. For marine applications, this is usually not a drawback.
AVL prices are comparable to an MDT and start at about $1,200 for just the GPS receiver that transmits location information back to a base station. A useful GPS receiver should also be able to receive polling signals from the base, and this two-way capability adds to the cost for radios, modems, etc.
After you buy the GPS receiver, you still have the same radio requirements of an MDT--transceiver, base station, etc. If you already have an MDT system, the comm channel can be shared.
Integrating With CAD
The responsibility for linking Schaumberg's GPS technology to computer-aided dispatch (CAD) AVL belongs to Integrated Computer Concepts (ICC) of Arlington Heights, Ill.
Dan Monopoli, president of the company, says this is ICC's first AVL site, although ICC serves 34 other sites in 11 states, covering about 60 different agencies.
He admits that five or six years ago he thought MDTs were an expensive toy. "I was proven wrong. I'm sold 100 percent on MDTs," he says now. "My feeling is that MDTs are the absolute answer to the redistribution of workload."
The dispatcher's position is a bottleneck for information, say Monopoli. "They're being hit on all sides. By allowing MDTs in the car, you can redistribute workload, which let's the dispatchers do their job better--to get the best information they can from the in-coming caller."
He sees enormous productivity gains at agencies with MDTs and says his company doesn't see a single bid that doesn't require them. "My feeling is that MDTs are mandatory devices, and AVL will be the same way within the next five years."
At Schaumberg, the AVL data is being transmitted on the police MDT network, rather than on a communications link of its own. Each time the officer sends an MDT message or status change, the car's location and speed data is transmitted, too.
Monopoli says his company is working toward total integration with CAD, to "work towards a nearest-available-unit concept of dispatch, on a real basis as opposed to a zone basis."
"The next step for us is application code that says, `OK, you know where the incident is. Go find the nearest available car,'" Monopoli says.
When that program link is finished, vehicle and incident locations will both be displayed on the same screen. Unit and incidents will be color-coded to indicate their status and CAD will recommend the closest unit based on actual locations.
An even more sophisticated application--queued recommendations for non-emergency units--is, "down the road," according to Monopoli. Within a year, ICC will have this unique system running at the Tulsa EMS Agency.
"We're going to be taking the technology even further," Monopoli says, "because we're going to be using the mapping technology to determine the fastest route to the call."
Best routing applications have been done for mass transit or package express, but most are based strictly distance, Monopoli says. "For public safety, we're doing it based on the fastest route, not necessarily the shortest. We're taking many, many, many factors into account."
The EMSA technology will include one-streets, left and right turns, street lights, 2-lane versus 4-lane, average speed, temporary barriers, and construction. "There are going to be all these factors built into the intelligence of the system so that it will calculate the fastest route," says Monopoli.
"Dispatchers have a very difficult job, and these tools help them make decisions better by giving them more instant access to information."
As for those children, satellite-gazing on a summer night, they probably didn't care about the rush of technology. They just liked trying to count the stars.*
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