2. Data
The measurement was performed during summer (August) 2008 in Vero Beach on the eastern coast of Florida (27°N, 80°W). The measuring base station is located at Vero Beach Marine Laboratory, owned by Florida Institute of Technology (FIT) and is situated about 200 m from the sea. Vertical electric field (both slow and fast fields), 3 MHz, 10 MHz and dE/dt of lightning generated electric fields were measured using four parallel flat plate antennas. The oscillators tuned to 3 and 10 MHz were operating at −3 dB bandwidth of 264 and 2020 kHz, respectively. All antennas were placed side by side, separated by 1 m, and about 20 m from the control room where the recording systems were kept. Signals from flat plate antennas were fed into two 4 channel digital transient recorders (12-bit Yokogawa DL1640L and 8-bit LeCroy 9314 DSO) using 25 m long RG 58 coaxial cable and properly terminated to avoid reflections. The DSO operated at a sampling rate of 100 MS/s has been set to work in a 40 ms pre-trigger mode so that signals before and after trigger pulse could be obtained. A 60 cm long coaxial cable (RG 58) was used to connect the antenna and electronic buffer circuit. The rise time of the fast antenna system for step input pulses was less than 30 ns while the decaying time constant is 13 ms to avoid over-loading due to large static field changes produced by close lightning flash. The decay time of the slow antenna system is about 1 s. Details of fast and slow electric field antenna's measuring system is similar to the one explained by Cooray and Lundquist (1982). Further, the triggering window has been set to window triggering mode, so that flashes with both polarities will be captured.