On Passive Emitter Tracking in Sensor Networks

Abstract

Many applications require fast and accurate localization and tracking of non-cooperative emitters. In many cases, it is advantageous not to conceal the observation process by using active sensors, but to work covertly with passive sensors. The estimation of the emitter state is based on various types of passive measurements by exploiting signals emitted by the targets. In other applications there is no choice but to exploit received signals only. Typical examples include search and rescue type operations. Some passive measurements can be taken by single sensors: e.g. bearing measurements (AOA: Angle of Arrival) and frequency measurements (FOA: Frequency of Arrival). The emitter state can be estimated based on a set of measurements of a single passive observer. This problem is called the Target Motion Analysis (TMA) problem which means the process of estimating the state of a radiating target from noisy incomplete measurements collected by one or more passive observer(s). The TMA problem includes localization of stationary as well as tracking of moving emitters. The TMA problem based on a combination of AOA and FOA measurements is considered by Becker in (Becker, 2001). Becker investigates and discusses the TMA problem with many characteristic features such as observability conditions, combination of various types of measurements, etc., (Becker, 1999; 2005) . Alternatively, measurements can be obtained from a network of several spatially dislocated sensors. Here, a minimum of two sensors is often needed. Measurements of Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) belong to this group. TDOAmeasurements are obtained in the followingway: several distributed, time-synchronized sensors measure the Time of Arrival (TOA) of signals transmitted from the emitter. The difference between two TOA measurements of the same signal gives one TDOA measurement. Alternatively, TDOA measurements can be obtained by correlating signals received by the sensors. A time standard can be used for time synchronization. 13