A second order gradient technique for an improved estimation of soil parameters in a two-layer earth

The method presented makes it possible to achieve the absolute minimum of the objective function, without constraints, by checking the value of the first order gradient component; when the first order gradient technique is unable to achieve a significant improvement in terms of decreasing the value of the objective function, then a Newton-Raphson based second order technique is used. As the objective function, a classic least squares fitting function is used. Results obtained are presented and compared to those of other methods. The characteristics of computer implementation and the average execution time are indicated. The iterative process does not require the guessing of any special starting point, and achieving the absolute minimum (gradient components less than a predetermined value) is guaranteed provided that the earth can be modeled as a two-layer earth