Mostly used lightning detection method in the past was Magnetic Direction Finding (MDF) method. Method was based on detection of lightning strike electromagnetic wave direction. Later, Time Of Arrival (TOA) method was developed. TOA method measures time difference from lightning strike hit to lightning strike detection by sensor. Based on that time, distance of lightning strike form sensor to lightning strike hit point is determined. Modern sensors nowadays uses combined method for lightning strike detection. With combined method time and location of lightning strike is accurately determined.
Magnetic Direction Finding (MDF) method
To determine lightning strike location with MDF method at least two sensors are needed. Sensors detect azimuth (angle between north and direction towards lightning strike) between the sensor and lightning strike hit. That is the way to determine line through the sensor and lightning strike hit point. With at least two lines (from two or more sensors) intersection of those lines is calculated. Intersection represents the exact logacion of lightning strike hit.With the use of several sensors we reduce the lighting strike position ofset.
In the above picture is shown how we determine the direction toward lightning strike. Elecric field caused by lightning strike, causes the magnetic field (vector marked with B). The magnetic field is always perpendicular to electric field, so with the determination of magnetic field, lightning strike direction is determined. With two or more sensors the exact location of lightning strike can be calculated.
Time Of Arrival (TOA) method
To determine exact location of lightning strike on TOA method at least three sensors are needed. Each sensor is GPS synchronized, so each sensor knows the exact time in UTC and its location. Accuracy of time detection is about 300 nanoseconds. In TOA method time differences between sensors and lightning strike are compared. Central analyser calculate lightning strike location. Each sensor gaves a hyperbola which represents possible lightning strike locations.
Lightning strike location determined with three sensors, is accurate only, if it is somewhere inside of triangle determied with those three sensors. Each par of sensors determine one hyperbola. Three sensor gives three hyperbola which intersects in one point.
If the lignting strike location is outside of three sensors triangle, two possible lightning strike locations are given. In that case at least one additional sensor is needed to determine lightning strike exact location.
New generation of sensors uses TOA and MDF method. This method is also named Combined method. Those sensor provides azimuth between sensor ang lightning strike hit point and exact UTC time. With those sensors exact time and location of lightning strike is determined.This method has no problems that are specific to a particular method. With using Combined method only two sensors are enough to determine lightning strike position. More sensors contributes to accuracy of lightning strike time and position.
First dirrection vectors are used for ligtning strike position evaluation, then with the time differences the exact lightning strike location is determined.