Handbook for the Extremely Low Frequency (ELF) Data Acquisition and Analysis System

Abstract : This handbook describes the digital data acquisition system built to record data in the 1 Hz to 600 Hz bandwidth from the portable underwater extremely low frequency (ELF) electromagnetic sensor unit. The sensors supported by the acquisition system are three-axis alternating magnetic field detection coils, three-axis alternating electric field sensors (electrodes) and three-axis seismic sensors; plus ancillary sensors such as pressure-depth, inclination and compass heading. The data acquisition system consists of the wet-end electronics package incorporating the controller board, 16 bit analogue to digital converter, low noise preamplifiers etc. and the dry-end electronics unit incorporating the power supply and computer. The data acquisition software for remote control of the total system and the analysis software which is linked to the data acquisition system is also presented. The analysis software which is purposely designed as an integral part of the acquisition system provides frequency domain spectral information (via the fast Fourier transform (FFT) algorithm) from the raw times series data and may be used both for quick look analysis during the data acquisition phase and for full analysis of data in slow time. (MM)