Detecting Object Movement through the use of Two GNSS Satellites

Monitoring using GNSS technology has played a very important role in tracking all manner of items, ranging from dangerous firearms to cash, and to the tracking of stolen vehicles. In different environments there will be times when the surroundings pose problems to the GNSS receiver, such as in the case where shipping containers are being stacked on top of each other, thus limiting the view of the receiver to the open sky. This paper introduces a technique for detecting whether an object has moved from its desired location using measurements from two satellites. This system uses a Time Difference of Arrival (TDOA) measurement obtained from the two range measurements and compares it with the theoretical value calculated using the ephemeris data. By taking the difference of the measured and the calculated TDOA values we are able to obtain a residual in which a probabilistic approach is used to assess if an object has moved from its desired location.