Application of time domain filtering to acoustic signals received at distances of greater than 3000 km has allowed oceanographers to extract modal information for a number of modes greater than the number of elements in the array. A model-based iterative algorithm has been developed to estimate the range of the source from the normal mode arrival time differences. The algorithm was applied to the acoustic engineering test of the acoustic thermometry of the ocean climate (ATOC) project. The modal amplitudes were used to then determine the source depth successfully. Successful localization implies that the source information has not been lost completely. This places an upper bound on the amount of internal wave-induced mode coupling that can be occurring. The bias in the range estimator is caused by internal wave-induced mode coupling and can be used as a measure of the internal wave strength. Results from the ATOC95 experiment at larger ranges (3500 and 5500 km) will be presented as well.