An error in the computation used to generate Figure 2 of this paper has been discovered. There should be no discontinuity in this figure and any reference to such a feature in the text should be ignored. The intent of the figure was to illustrate the extent of nonorthogonality in 1-D EM controlled source fields.
Figure 5 was also found to be in error. The proper version of both figures appear here. These errors occurred only in the display of the date; quantitative calculations in the paper and the conclusions resulting from the analysis are not in error.