Interactive computing and graphics in the interpretation of geomagnetic spectra

Abstract

Transformations of spectral estimates of sampled geomagnetic data have been developed to facilitate the analyses of digitally recorded signals. Exploratory data analysis is performed by visual inspection of multi-dimensional displays created on graphic recording devices and the storage tube of a graphics terminal. Programs allow the on-line user of a large computer both to process and to view graphs of selected data after various transformations. Simple keyboard commands executed by interactive programs expedite the selection and examination of transformed data. Systematic patterns, discerned on the CRT display, are permanently recorded by an attached hard-copy graphic unit on a photographic print. Useful graphic techniques developed include 3-D isometric plots, histograms and multiple function displays. To utilize fully the interactive graphical analysis capabilities, a number of signal selection and transformation programs have been implemented. These include a post-whitening transform applied to geomagnetic spectra spanning the ⋍0.3–⋍63-mHz band and a number of smoothing and non-linear amplitude normalization transforms for facilitating visual comparisons of the morphology of signal estimators viewed as functions of time and frequency. The main results are programs implementing computer techniques for organizing, processing and transforming geomagnetic spectra.