Automatic calculation of electron density profiles from digital ionograms: 3. Processing of bottomside ionograms

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Abstract
Automatic scaling of bottomside Digisonde ionograms gives the E and F region echo traces with high accuracy. Polarization and incidence angle information in the ionogram enables the extraction of the vertical, ordinary polarization echo trace from quiet as well as disturbed ionograms. The scaling algorithm is tested with Digisonde ionograms from Goose Bay, Labrador, which show spread F about 50% of the time. Despite these disturbed conditions, f0 F2 is determined within ½ MHz for 475 ionograrns out of 577 during January 1980. A profile inversion algorithm calculates the electron density profile from the autoscaled h′(ƒ) points. Parabolic profile shapes are assumed for the E region and the valley between the E and the F layer. The F layer is approximated by a single sum of Chebyshev polynomials, and the entire profile is described by a set of 16 numerical values. The CPU time required for ionogram scaling and electron density profile calculation is 14 s on a Cyber 71 computer. In addition to the profile the program outputs all relevant ionogram parameters: critical frequencies, minimum virtual heights, frequency and range spread, average echo amplitudes, and Doppler shifts.