FILTER COEFFICIENTS FOR OFFSET WENNER AND WENNER RESISTIVITY SOUNDINGINTERPRETATION

New efficient sets of filter coefficients for computation of apparent resistivity and resistivity transform curves for use with the Offset W enner and Wenner electrode system have been derived and tested. The ne w coefficients have been optimized for step models with resistivity co ntrasts ranging from 0.99 to -0.99, which simulate the extreme situati on of wideband input for forward and inverse filters. The filter sampl e interval has been selected as In 2, the same as the interval between data points on the sounding curve obtained with the Offset Wenner sys tem, so that it is not necessary to interpolate between datum points d uring computation. The tests on 20 step models with strong resistivity contrasts have shown that the largest relative errors obtained with t he new coefficients (twelve-points for forward and eleven-points for i nverse) are about one order of magnitude smaller than published short filters for the Wenner array. Improved filter coefficients for Wenner sounding with a sample interval of (1/3)ln 10 also have been derived a nd tested. A computer program in FORTRAN 77 to generate Wenner soundin g curves is included.