On the Manual and Digital Computer Methods Used at Lindau for the Conversion of Multifrequency Ionograms to Electron Density‐Height Profiles

Abstract

Real‐height analysis of multifrequency ordinary and extraordinary virtual‐height traces has been carried out at Lindau since 1956 with methods of our own design. They all take account of underlying ionization and extrapolate the real‐height profile up to the peak of the layer under discussion. This extrapolation is based on observed virtual heights rather than on deduced real heights. At least second‐order approximations of the profile are used here. All of the methods allow for analysis of monotonic and nonmonotonic virtual‐height traces. They differ only in their final accuracy. A model method is described first; only 8 min are necessary to reduce a simple F trace. The respective real‐height data have proved very useful for statistical purposes. Since 1957, very accurate and general manual methods have been in use. One and one‐half hours are necessary for a full analysis of one ionogram. While these methods rely on an estimate by eye of the critical frequency of the layer of interest, the digital computer method in general use at Lindau since 1962 deduces this value too. The accuracy of this digital computer method is much better than the technical accuracy of the present ionosondes. A complete real‐height analysis of one virtual‐height trace, showing a critical frequency of 16 MHz, amounts to about 14 min of computer time (IBM 650). Test results on a series of theoretical ionograms of monotonic and more or less complicated non‐monotonic electron density‐height profiles, valley profiles, are also reported.