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Sensors are usually deployed in a region to observe the activity in an area of interest. Different sensors are deployed to observe the different activity. Acoustic sensors are deployed in a battlefield or in an urban area to monitor acoustic activity – the presence of tanks in the field. In urban settings, acoustic sensors can be deployed to detect a congregation of people and the general nature of such a congregation, that is, whether the crowd is hostile or peaceful. The deployed acoustic sensors record the sound waves emanated in the vicinity and transmit to a remote hub or a central observation center where the data (sound waves) is analyzed. The type of analysis depends on the type of activity for which one is looking. Tracking vehicles in a field may comprise use of a tracking algorithm, while detecting people in the field may require an entirely different algorithm. In any case, the data analyzed has to be referenced to the location of the sensor. Without knowledge of the sensor location, the data has no relevance.
In a battlefield or in covert operation situations, the sensors may be deployed using an airborne vehicle such as a helicopter or airplane. Whatever mechanism is used for deploying the sensors, the location of the deployed sensors may not be available. It is possible to guess at the general vicinity where the sensors will land based on the location of the deploying vehicle, the speed at which the vehicle was flying, the angle at which the sensors were hurled, general wind speeds in the vicinity, and the direction the vehicle was traveling.
Army researchers have developed a device to locate sensors. The apparatus includes a processor that receives sensor node data and object trajectory information data for an object. The sensor node data is related to the object from which the bearings of the object can be estimated which in turn are related to the trajectory of the object, and a data point in the object trajectory information data comprises a time stamp and the coordinates of a position. The position corresponds to the location of the object at the given time. The processor is adapted to use several bearing estimates from the sensor node data and the corresponding position information of the object to determine an absolute position of the sensor node.
The method can be broadly summarized by the following:
- Collecting object trajectory information data for an object over a time span
- Acquiring sensor node data over the same time span and is related to the object trajectory information data
- Determining several direction indicators, each providing an approximate bearing from the sensor node to the object at a given instant of time during the time span the data is collected
- Determining coordinates of the sensor node using a portion of the collected trajectory information data and the corresponding direction indicators (bearings) determined by the sensor node data
- US patent 8,060,338 is available for express licensing