The Time-of-Arrival (TOA) technique utilises the difference in time when the electromagnetic signature of a lightning flash is detected by two or more sensors within a network. GPATS has developed the advanced lightning positioning system based on the Time-of-Arrival technique.
Time Difference of Arrival (TDOA) Technology
The detection network uses a Time Difference of Arrival (TDOA) technique applied to the transmission from a radio signal source which is a stroke of lightning. This TDOA technique is based on the time differences between the receptions of a radio signal at three remote receivers at known points from a single source at an unknown point. Each signal, traveling at the speed of light, approximately 186,000 miles per second, is time-stamped by the receivers at the three known points. The time-stamp differences are then used in highly complex hyperbolic curve generation calculations to locate the source of the unknown radio signal. In general, this method defines hyperbolic curves by their arrival time differences at the known receivers, (R1, R2, R3). The point of intersection of two hyperbolic curves defines the location of the source of the radio transmission (the location of the lightning stroke).
Only three receivers are needed for the hyperbolic calculations, but more than three receivers may intercept the same signal. With more than three receivers reporting, we have redundant information available to improve accuracy calculations and verify the performance. Furthermore, our network monitoring program can also use the redundant reception to automatically monitor receiver performance. The system monitoring function also determines whether or not a redundant receiver that should have received, processed, and transmitted a signal’s data to the central analyser received the data.
If a sensor is seen to have problems and needs diagnostic interrogation, it is a simple matter to access and operate a remote diagnostic program on the network. All GPATS receivers can be accessed remotely. This allows an operator at the Central Analyser Processor (CAP) with communication links to the CAP or receiver to perform periodic diagnostic tests for over a dozen receiver and sensor functions. This very powerful design feature means that maintenance adjustments can then be made or upgraded software can be downloaded without visiting the receiver site. Furthermore, because much of the hardware has been designed to be under remote software control through special devices known as Field Programmable Gate Arrays (FPGAs), the receivers’ hardware design can also be reconfigured from a remote location which is typically over the Internet.
The receiver is unaffected by buried or overhead powerlines as well as other sources of electromagnetic field anomalies which make site selection and preparation such a costly matter for users of MDF-based lightning location systems.