Internal waves have been shown to cause significant mode coupling for long-range acoustic transmissions [Colosi and Flatte, J. Acoust. Soc. Am. (in press)]. This coupling produces a variance and bias in a modal arrival time difference range estimator and a mode space depth estimator. The bias and variance induced by internal wave coupling is quantifiable. An inversion is therefore possible for the background strength of the internal wave field. The structure of the mode arrival time bias provides information on the depth of maximum internal wave activity. The success of the depth estimator reveals the limit of internal wave-induced mode coupling and places an upper bound on the energy in the Garrett--Munk spectrum. Broadband long-range simulations through internal wave realizations will be presented, quantifying the effect. Results from experimental data along different propagation paths (AET and ATOC95) will be presented, and an estimate of the internal wave strength parameter will be given for each.