Systematic distortions of the spectrum of the signal scattered from diffusive media, and limitations on the resolutions in frequency and altitude due to the finite receiver bandwidth and the finite transmitted-pulse duration are estimated, using the radar-ambiguity function. The requirements for frequency and altitude resolutions are incompatible in the filter-bank method (FBM) which directly measures the power spectrum. With the actual parameters of the ionosphere, the FBM is shown to be inconvenient for pulse radar measurements except those of higher altitudes and/or with higher radar frequencies. In the correlation-function method (CFM) which calculates the cross-correlation or autocorrelation function, the resolutions are independently determined in frequency and altitude. The pulse duration is concerned only with the resolution in altitude. The minimum duration is limited by the sensitivity of the radar system, while the maximum is limited by the characteristic time of fluctuations in the medium which scatter the radio waves. Various methods for measuring the autocorrelation function are also described
