Exploration Geophysics - Volume 20, Issue 3, 1989

The Cumulative Difference Statics (CDS) method, applied to routine reflection profiles in areas of rapidly-changing near-surface weathering, provides a robust and accurate estimation of static corrections using the first-break refraction data. The method uses the first-break arrival times of refracted energy between paired shots to track the variation in the travel-time through the weathered layer. Comparison of the CDS method with conventional refraction static methods in basement areas illustrates the ability of the CDS method to handle the rapid variation in the static corrections which often occurs in these areas. The CDS method can be readily applied to the problem of calculating the static corrections for both two and three dimensional seismic surveys.

Exploratory drifts and boreholes are classic methods used in mining when searching for ore. When geology is complicated, workable mineralizations may remain undetected.

Attempts to explore for ores using radio waves were made as early as the 1950s. Short-wave electromagnetic radiation is transmitted through the rock. Ore absorbs more energy than the surrounding rock, thus creating a "radio wave shadow" (RWS). The RWS method was developed as a multifrequency method by the BGR to a stage that can be used for routine work. In cooperation with the BBU, this method has been used for underground exploration for lead-zinc ores since 1982. It has proved to be a useful, modern miners tool.

The one dimensional objects commonly sought by ground probing radar produce characteristic hyperbolic signals on radargrams. In areas of high noise or clutter these hyperbolae may be difficult to detect. Standard migration techniques can be used to help detect these objects in such areas, however the use of additional constraints concerned with the coherency of the hyperbolic signal can be substantially more effective.

In situations in which Gaussian error assumptions are not valid, estimation procedures based on the least squares (LS) algorithm can be seriously misleading. It is then essential to use statistical procedures that are robust, in the sense of being relatively resistant or insensitive to the presence of a moderate number of outliers (abnormal data) superimposed on a common Gaussian noise background. This paper demonstrates the implementation of the robust regression M-estimate to magnetotelluric (MT) data. Like the LS estimate, the M-estimate minimizes the difference between prediction and observation, but it differs from the LS estimate in that it defines the measure of misfit in a way that does not allow a few bad points to dominate the estimate. Starting with the description of this estimate, several algorithms for computation are discussed and applied to estimate MT impedance. Using synthetic and real data, it is shown that, in comparison with the remote reference (RR) method (which is based on LS), robust procedures yield impedance estimates that are no worse than RR, and are often better.