Monday, September 16, 2002

Tricks of the Trade
By Private Investigator Michael T. O'Rourke

Question: I am a paralegal with an attorney specializing in criminal defense. One of the pieces of evidence implicating our client in a theft charge is “GPS” data accumulated from the company truck he was driving. What is GPS, and how does it work?

Answer: The company vehicle appears to have been equipped with a AVL. Automatic Vehicle Tracking (AVL) combines computer technology with satellite tracking technology (GPS; Global Positioning Satellites). The AVL unit can be mounted covertly by the vehicle owner. This is common practice in the transportation industry. This type of surveillance system calls for three basic elements: satellites, sender/receiver units, and location decoder software.

The U.S. Department of Defense has placed a series of 24 Global Positioning System (GPS) satellites in orbit around the earth. These GPS satellites broadcast signals that contain time and identification codes. GPS receivers use an antenna to acquire these signals from multiple satellites to determine the vehicles' position, altitude, speed and direction of travel. The signal is gathered by the GPS unit every six seconds. The information is then stored in the GPS unit for further interpretation.

The heart of a GPS receiver is the ability to find the receiver's distance from four (or more) GPS satellites. Once it determines its distance from the four satellites, the receiver can calculate its exact location and altitude on Earth. The GPS receiver measures the amount of time it takes for the signal to travel from the satellite to the receiver. The receiver looks at all the signals it is receiving and uses calculations to find both the exact time and the exact location simultaneously.

There are two types of receiving systems: real time satellite tracking systems and none-real time systems. Real time tracking systems forward the received data through a cellular phone modem to the Investigators' computer. In none-real time tracking systems, the satellite signal is electronically stored. With this simpler type of system, you retrieve the unit after the surveillance and then load the data into your computer.

No matter what type of GPS tracking system is used, some sort of power supply is needed. In the typical temporary magnetic/velcro mount systems, standard battery power can be used. The typical battery unit lasts 24 hours. For surveillances of greater duration, you would hardwire the unit to a power source on the vehicle.

The decoder software converts the data received into latitude and longitude. This information is further refined with mapping software so the user can observe actual maps of the location of the target vehicle, including street names, and the duration of the signal. Not only can you determine where the vehicle traveled, but how long the vehicle remained at a certain location.

Retrievable GPS units, including mapping software can be obtained for under $500. Additional uses include employers tracking company owned vehicles, parents monitoring a childs’ use of the family sedan, or overtly as a mapping tool. GPS Units have allowed the investigator to utilize unmanned surveillance techniques to gather valuable information for a very reasonable cost.

Det. Michael T. O'Rourke is a Member of the National Association of Investigative Specialists, The National Association of Professional Process Servers, and Sustaining member of the Delaware Paralegal Association. A Court Certified Special Process Server, and a Licensed Private Investigator in DE and PA. Michael specializes in Insurance Defense and Criminal Defense. He invites your questions to:

Loss Solutions, Inc.
824 N. Market Street,
Suite 425, P.O. Box 368,
Wilmington DE 19899-0368.
(302) 427-3600.

Or you may e-mail him at

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