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The Technology
In a time-of-arrival based system, precision timing is a critical part of the receiver. The PLS receiver uses commercial GPS timing as a reference, and has an accuracy of 15 nanoseconds. The sensor uses a high-frequency timing source that makes the timing more stable and accurate, and increases the resolution. The timing is constantly monitored and corrected, resulting in more accurate lightning locations. An onboard processor manages communications and monitors the overall operation of the sensor.
PLS sensors utilize proprietary low frequency detection methods and waveform discrimination to allow the network to calculate and display the location where the stroke hits the ground. Other lightning systems report the location where the event passed through the cloud, which is typically several hundred meters above the ground and can be offset from the actual point of impact by many kilometers.
Cloud lightning generates much higher short-term energy at higher frequencies than cloud-ground strokes, which the PLS sensors will identify. The precise timing of a cloud pulse of a certain magnitude will allow the very accurate location of that pulse using time-of-arrival mathematics. Due to their very high sensitivity, PLS sensors have no problem detecting cloud stroke signatures, but because of the comparatively weaker peak voltages received at the antenna and the effects of propagation delays over longer distances, signal strength thresholds will also be lower than for ground strokes.
It is well established in the scientific literature that a cloud flash typically has a magnitude equivalent to 3 - 5kA ground stroke. That is the signal strength used in the analyses of detection efficiency and location accuracy that have been performed for cloud stroke events. Furthermore, the analysis is based on the general rule that around 3-4 cloud strokes typically occur for every ground stroke. Based on these guidelines and the analysis of lightning data from TOA’s networks in the USA and Australia, it has been verified that the PLS detects a high percentage of the cloud lightning events occurring within the network. The detection efficiency and location accuracy for cloud lightning is dependent on the number of sensors comprising and the overall geometry of the network.
The system is designed to communicate using a variety of different means, such as the Internet, serial port, satellite communications, or modem communications.