A method is provided for non-intrusively determining cross-sectional variation of a fluidic channel. The method includes creating a pressure pulse in a fluidic channel using a hammer to strike an external surface of a fluidic channel. The method also includes sensing, by one or more sensors, reflections of the pressure pulse; and obtaining, from the one or more sensors, a measured pressure profile based on the sensed reflections of the pressure pulse. A forward model of cross-sectional variation of the fluidic channel is generated based on a baseline simulation. Using the forward model, a simulated pressure profile is generated. Using the measured pressure profile and the simulated pressure profile, an error is determined. When the error is outside a predetermined threshold, the forward model is updated based on the error. An estimate of cross-sectional variation of the fluidic channel based on the forward model is displayed.