Over the past five years we have performed an extensive series of experiments on hydrodynamic (Rayleigh–Taylor) instabilities. Typically such experiments involve the time‐resolved radiography of an accelerated foil (planar geometry) with the line‐of‐sight of the radiograph along the direction of motion. In comparing experimental data to simulations, the simplest approach is to extract the modulation in exposure level of such a radiograph versus time and compare the inferred growth rate (assumed to be exponential) with the growth rate in column density (&Dgr;&rgr;z) from a simulation. We have found that this gives unsatisfactory results. We will discuss the techniques for experimental analysis and post processing of simulations which we use for a more direct comparison of the data with the simulation, including the extraction of Fourier components versus time from the data, the effect of backlighter spectra, emission from sources other than the backlighter, and the nonlinear effects of instrument response.