The coherent-mode representation (CMR) of an optical random source is a very powerful tool in contemporary optics. However, the practical value of the CMR is essentially restricted because of the complexity of solving the Fredholm integral equation with the source cross-spectral density as a kernel. Moreover, in practice, the analytical expression for the cross-spectral density of the source, as a rule, is unknown, a fact that makes this solution impossible in general. Here we propose a technique for the determination of the source CMR that does not involve solving the Fredholm integral equation but is based on usual radiometric measurements. We illustrate the proposed technique with the results of mathematical simulation.