The complicated patterns of modal structure and attenuation observed in sound propagation through a range-dependent shallow-water environment are used to investigate and visualize the mechanisms of mode coupling and stripping. Broadband experiments have been carried out at the geologically known AGS site in the past few years. This presentation reports on a recent experiment which provides significantly more acoustic data along different propagation tracks and, consequently, permits high resolution of physical processes in range. A mode-filtering technique is used to construct modal structure from the data, while modal attenuation is obtained from spectral ratios. The evolution of modal structure is determined as a function of frequency and range. This is examined in view of environmental parameters along a selected propagation track. Numericalsimulations are carried out using interpolations of the known geoacoustic environment and employing the KRAKEN normal mode and RAM parabolic equation models. Results from these simulations are compared with the experimental data.