On the spectral analysis and interpretation of incoherent scatter plasma line echoes

This paper describes a model of the physical interactions involved in incoherent scatter that result in specific plasma line spectral shapes as a function of range and frequency. This model is quite successful in duplicating the naturally occurring plasma line spectra observed at high latitudes. Moreover, the inherent sensitivity of the data collection method suggests a much more general applicability. For example, we will demonstrate a sensitivity of the method to plasma density irregularities in the medium that rivals or exceeds that possible with radio wave scintillation techniques. Unlike height‐integrated scintillation measurements, however, this new method can range resolve the fluctuations in plasma density. We are able to determine the altitude of the F layer peak to an accuracy of ∼ ± 1 km even with a probing pulse of 72 km in length. Our density fluctuation measurements indicate a residual level of ∼ 1% fluctuations after a linear‐temporal trend is removed. This indicates spatial variations in plasma density of this order within our relatively narrow (0.5°) antenna beam. These spatial variations are enhanced during periods when the F layer peak cutoff frequency is decreasing. Such behavior is consistent with increased plasma structure on the trailing edge of F region plasma blobs. Our technique involves not only model fitting but also a data collection method that minimizes range smearing. This data collection mode has already been successfully implemented at the Sondrestrom, Greenland, incoherent scatter radar facility.