8-12 July 2013
Extraction of surface impedance from magnetotelluric data
Presented by Mr. Sfundo KHANYILE on 9 Jul 2013 from 16:00 to 16:20
Type: Oral Presentation
Session: Space Science
Track: Track D2 - Space Science
This paper presents the analysis of South African magnetotelluric (MT) data in the time and frequency domain for the purpose of extracting representative values of surface impedance. The surface impedance is used in the derivation of geo-electric fields produced by rapid variations in the geomagnetic field, as occurs during geomagnetic storms. The magnetotelluric method uses the spectra of associated time varying horizontal electric and magnetic fields at the Earth’s surface to determine a frequency dependent impedance tensor and an equivalent surface impedance. The theory of operation of MT devices will be presented, as well as typical data obtained from the MT installations in Hermanus, Vaalputs and Middelpos. The various steps in the analysis are aimed at reducing noise and outliers. In the time domain, a Hanning window is used to select data from successive periods during a day, while reducing the end effect (Gibbs' phenomenon) by tapering the series towards the start and ends of each selected time period. The spectral transformation is performed by means of a fast Fourier transformation (FFT). Spectral bands are selected by frequency domain filtering. Typical results and challenges in performing this analysis will be presented.
Dr P Cilliers