Calibration of the BF-4 Magnetic Field Induction Sensor and the Algorithm of Lightning Related Charge Moment

Abstract

To explore the physical connection between transient luminous event and associated
lighting, a magnetic field measurement system at the band-pass of extremely low frequency
was established at Lulin Observatory in 2003. This system mainly consists of a
pair of high-sensitivity BF-4 magnetic field induction sensors and a signal modulator.
Two problems were already revealed and noted by the previous work of Wang [2004],
one is the waveform distortion caused by the signal modulator, and another one is the
un-calibration of magnetic field coils. These problems prevent the data recorded by this
system in the past years to be used confidently in the scientific applications. In this study,
a mathematic work based on the Fourier theory and related experiments are proposed to reconstruct the distorted waveforms. The validations by various waveforms show this approach is functional at the frequency range of 1-117 Hz. A long solenoid was built to produce a uniform magnetic field to calibrate the amplitude and phase responses of the BF-4 sensors over several decades of frequency. An event of an intense lightning with TLE is applied to derive the charge moment change based on the wave guide model of electromagnetic wave propagation between Earth and ionosphere.

Date of Award	2009
Original language	English
Supervisor	Bing-Chih Chen (Supervisor) & Rue-Ron Hsu (Supervisor)