Passive Geolocation with 3D TDOA

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  • Author: Dr Michael Knott & Dr Alasdair Edge

The concept of using radio frequency (RF) waves to locate objects is one that will be familiar to anyone acquainted with radar. Radar systems send short pulses of radiation out in a known direction, and then wait for any return signal that has bounced off an object in that direction.The range of passive geolocation techniques includes Angle of Arrival, Power of Arrival and Time Difference of Arrival. Angle of Arrival (AoA) uses at least two directional antenna arrays, each of which detects the direction from which the transmission originated. By extending lines of bearing (LOBs or LOB) out in those directions from each array, we can roughly locate the source at the intersection of those lines. Power of Arrival (POA) uses the fact that the power of signals drops off with distance traveled. 

By measuring the differences in the power received at two different locations, we can determine how much farther the source is from one location than the other. If we have at least three receivers, we can use this information to determine the source location. In this whitepaper, we will focus on the passive technique known as Time Difference of Arrival (TDOA), which uses the time difference between receipt of signals at spatially separated receivers to determine the location of the source.

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