Bispectral analysis of meter wavelength interplanetary scintillation

The bispectrum of interplanetary scintillation is investigated. Rice-squared and lognormal point-source intensity probability density functions are used to derive model bispectra as functionals of the intensity autocovariance. Simultaneous observations of the source CTA 21 at 270, 340, and 470 MHz are analyzed to produce scintillation indices, skewness parameters, and bispectra, which are compared with the models for the cases of weak, intermediate, and strong scattering. The results obtained for CTA 21 are shown to rule out lognormal statistics for interplanetary scintillation over the frequency range from 340 to 470 MHz. It is found that the observed bispectra correspond well with the predictions of the Rice-squared model for weak and intermediate scattering, but are systematically different from model bispectra computed by assuming a point source in the case of strong scattering.