A Marquardt, nonlinear, iterative inversion is applied to obtain the best-fit parameters for 7 spectral models of heterogeneities under NORSAR using the observed TCF (Transverse Coherence Functions) and ACF (Angular Coherence Functions) at NORSAR. The simplest model is a single-layer model with one power-law spectrum; the most complex model is a two-overlapped-layer model with two different power-law spectra specified by 6 unknown parameters. F-tests are performed for different pairs of models; the two-layer model with two different spectra is a significant improvement over the single layer, one spectrum model. The final results of nonlinear inversion agree with the Flatt¿-Wu spectral model for heterogeneities under NORSAR. ¿American Geophysical Union 1991