| Description: | The FORTE satellite detects transient electromagnetic events
associated with lightning using a suite of optical and
radio-frequency (RF) instruments. Data is collected with a sample
rate of 50 MHz for 800 microseconds. A Fourier transform is
performed on the input data to produce a spectrogram. The
spectrograms are then collapsed in frequency to produce a power
density time series, with 3181 samples in each time series. These
are then smoothed to produce series of length 637. The seven
classes are.
CG Positive: Initial Return Stroke
A positive charge is lowered from a cloud to the ground. The
characteristic feature of this type of event in the power density
time series is a sharp turn-on of radiation, followed by a few
hundreds of microseconds of noise.
IR Negative Initial Return Stroke
A negative charge is lowered from a cloud to ground. The power
waveform slowly ramps up to a level known as an attachment point,
where a large surge current causes the VHF power to 'spike'. This
attachment is followed by an exponentially shaped decline in the
waveform.
SR Subsequent Negative Return Stroke
A negative charge is lowered from a cloud to ground. As the name
implies, subsequent return strokes come after initial return
strokes. Note that subsequent positive return strokes don't exist.
I Impulsive Event
Typically an intra-cloud event characterized by a sudden peak in
the waveform.
I2 Impulsive Event Pair
Another intra-cloud event characterized by sudden peaks in the
waveform that come in closely separated pairs. These are also
called TIPPs (Trans-Ionospheric Pulse Pairs).
KM Gradual Intra-Cloud Stroke
An intra-cloud event which increases in power more gradually than
an impulsive event.
O Off-record
800 microseconds was not enough to fully capture the lightning
event.
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