Remote Magnetic Field Research Articles

On the Master, Uman, Lin, Standler and the Modified Transmission Line Lightning return stroke current models

We show that the lightning return stroke model by Master, Uman, Lin, and Standler (MULS), a modification of the Lin, Uman, Standler (LUS) model, can be viewed mathematically as having a specified channel‐base current, although in the original formulation it was the channel current sources that were specified. The specification of the MULS channel‐base current is independent of the time dependence of the corona current sources which characterize the MULS model. Further, we show that, when starting from the same channel‐base current, the MULS return stroke model, except for the uniform current component, is mathematically equivalent to the Modified Transmission Line (MTL) model. For both the MULS and the MTL models we present a single analytical expression relating the far fields and the channel‐base current. This formulation provides for a simpler procedure to infer MULS channel‐base currents from remote electric and magnetic field measurements than was previously available and hence to test experimentally the MULS model.

Current sensing using Faraday rotation and a common path optical fiber heterodyne interferometer

An optical configuration for a current sensor utilizing the Faraday effect is described. A common path optical fiber heterodyne interferometer is used to greatly reduce noise produced by environmental effects. A miniature sensing element at the distal end of the fiber allows remote magnetic field or current measurements to be made. Solenoid generated magnetic fields over the range 0.7 to 10 μT, corresponding to solenoid currents from 10 to 150 mA, have been detected over a frequency range from 25 to 125 Hz with a linear response.

Magnetotelluric data processing--a case study

SUMMARY Magnetotelluric (MT) data collected simultaneously at one or more sites may be processed by a number of different methods. Such methods attempt to remove or suppress the effect of noise on the data channels. The desired results are accurate, unbiased and repeatable estimates of the impedance tensor as a function of frequency and location. In this study we perform an investigation of the analysis of an MT data set sampled at 5s. Both single-site (SS) and remote-reference (RR) techniques are employed to estimate the impedance tensor 2. TWO biased SS estimates of 2 are used to compare the performance of five coherencebased acceptance criteria. It is demonstrated that the RR predicted coherence between local fields can be used for selecting data windows, and provides a necessary assessment of the reliability of a given RR estimate. It is demonstrated that the variance of an RR estimate depends strongly on the local signal-to-noise ratios (as monitored by the local predicted coherence) and depends weakly on the number of data windows, as long as coherences are above a moderate threshold. Although, for our data, an estimate of Z obtained using a remote electric field is grossly inaccurate, its associated predicted coherence is as efficient in selecting low-noise-level data windows as its counterpart obtained using a remote magnetic field. The relation between SS and RR predicted coherences, the latter estimated using both electric and magnetic fields, is investigated. A hybrid selection technique that uses a remote electric field is suggested.