Calculation of ionospheric conductivity profiles by inverting VLF/LF reflection data: 1. Isotropic propagation

Abstract

A method for inverting VLF/LF ionosounder data to obtain ionospheric conductivity profiles is described. The method is applied to altitudes below about 70 km, where the propagation can be assumed to be isotropic. Two cases are evaluated: (1) model ionospheres for which artificial data are generated by calculating reflection coefficients and (2) actual ionospheres for which reflection coefficients are measured by VLF/LF ionosounders during a strong solar proton event. Estimates are given of altitude ranges inside which ionosounder data contain information about conductivity and outside which the inversion breaks down. Calculated profiles are shown to agree well with model profiles within those altitude ranges. Profiles calculated for the solar proton event of September 23, 1978, are similar in magnitude and structure to those which occurred during earlier strong solar proton events.

Calculation of Ionospheric Profiles by Inverting VLF/LF Reflection Data. II. Anisotropic Propagation.

“…Field, Warren, and Warber [1983] applied the method to reflection coefficient data measured by ionosounders during a strong solar proton event (SPE), when propagation could be assumed isotropic. They presented physical criteria for determining the altitudes at which the inversion is reliable and those where it breaks down.…”