Lightning is responsible for more than 50% of all bushfire ignitions in Australia, with some estimates placing this figure closer to 70%.
A lightning storm can generate thousands of strikes, but only a very few are capable of igniting a fire.
We call these strikes High-Risk-Lightning (HRL).
Some of the HRL strikes will start a fire immediately and these will be detected using the BushfireLIVE cameras and Alchera’s AI detection. Other strikes will smoulder for hours, days, or even weeks and they can all ignite when the temperature and wind go up. Detecting these strikes with sufficient accuracy to be able to despatch a fire tanker or an aerial asset equipped with FLIR cameras and extinguish the hot spot before it has generated smoke is the holy grail of bushfire detection.
What is High Risk Lightning?
Essentially only a small number of lightning strikes are capable of starting a fire; these are termed High-Risk-Lightning (HRL) strikes.
Lightning can travel within thunderstorms, between clouds in the atmosphere and only around 25% strike the ground.
Most ground strikes are for a fraction of a millisecond and do not provide sufficient continuing current to ignite a fire. HRL strikes are for 200 milliseconds or more. This is 10,000 times the duration of a typical strike and have a significantly greater potential to start a fire.
The US National Weather Service states:
Lightning flashes containing continuing current are particularly important because they are more likely to start fires. In a typical return stroke, electricity flows for only a short period and does not generate the heat required to ignite a fire; however, in continuing current, electricity flows over a much longer period of time and will generate considerably more heat. Consequently, flashes with continuing current are much more of a fire concern.
The figure below shows a typical strike.
What Actually Happens?
Lightning descends from cloud to the earth and then a return current uses the path created by the initial strike to return to the cloud. These downwards and upwards strokes can repeat up to a dozen times or more all within a fraction of a second.
The FNN Hardware Detection Service
BushfireLIVE has partnered with Fire Neural Network in Florida to introduce the HRL detection service in Australia and globally.
The FNN Hardware Detection Service is based on FNN proprietary hardware which can be installed at each of our camera locations. This consists of an antenna and a control box which will be interfaced into our power and network solution.
The raw dual-band electric field output from the HRL detectors is transferred to an AWS server for processing.
The service comprises three components:
- HRL Detector
- HRL Locating Service
- HRL Downselecting and Alerting
The service will provide the following:
- Measurement of continuing current
- Location accuracy to 30 m
- 3D mapping of the HRL strike
- Correlation of the strike location and intensity with vegetation and fuel load data
- Assignment of a score to the strike which will estimate the potential for the strike to create an ignition
- Provision of a KMZ file showing the estimated location and the likely maximum area in which the strike could have occurred
This system has been operated in Florida in a test environment and Australia will be the first operational deployment globally.
3D mapping allows FNN to map out the detailed structure of the lightning strike. This is beneficial for two reasons:
- It enables FNN to see the charge pockets and accurately calculate current duration and charge transfer, which are essential for HRL detection.
- 2D methods average the locations of the emission sources along the lower part of the channel, which means that for non-vertical channels an error is introduced.
- 3D mapping means FNN can see where lightning strikes the ground, which means that the reported location of the strike is accurate.
The 3D map shows IC (In Cloud) strikes and CG (Cloud to Ground) strikes. The extent of the continuing current is also shown on the map
The exact location of the strike can be determined as shown by the black arrow at the base of the map