Evaluation of plasma‐wave spectral density from cross‐power spectra

The plasma‐wave spectral density is evaluated by performing a spatial Fourier transform on experimental cross‐power spectra of ion acoustic waves. The cross‐power spectra are recorded on analog magnetic tape, converted to digital form, transferred to digital magnetic tape, and Fourier transformed on a digital computer. The important effects of sampling, finite data strings, and data smoothing on the end results are discussed and illustrated. The results indicate the usefulness of the spectral density method for the study of nonlinear wave phenomena.