A SIMPLE METHOD OF BACKSCATTER IONOGRAM ANALYSIS

Quasi-parabolic (QP) ionospheric layers may be grouped into families based on the value of the ratio of layer to semi-thickness. The highest frequency which can be reflected from a QP layer, and the associated group path, can be used to normalize the leading and trailing edges of backscatter ionograms. When this is done, QP layers from the same family produce almost identical normalized curves. In principle these curves can be used to invert the leading and trailing edges of real backscatter ionograms to obtain the parameters of the QP layer which best fits the data. However, in practice the trailing edge is determined by the antenna pattern rather than the ionospheric layer. Consequently a simplified analysis method has been developed based on analyzing just the leading edge. Because the leading edges of the normalized curves do not vary greatly from one QP family to another, the method (and any other based on leading edge data alone), will not yield a unique QP family solution unless the data are very accurate and noise free. These conditions are unlikely to be met with real backscatter ionograms. Separate sections of a leading edge may be analyzed to give different QP layer fits to obtain, say, E-and F-layer parameters. However, the QP layers so obtained are best regarded as 'equivalent' layers which describe the propagation characteristics (e.g. group path and ground range) of the ionosphere quite accurately, but not the ionosphere itself. Futher development using trailing edge data is possible but requires an accurate knowledge of the antenna characteristics of the system being used. An important consequnce of these results is that backscatter inversion techniques capable of determining ionospheric layer parameters will need to be based on more than the analysis of the leading edge.