Mitigation of ion-temperature/composition ambiguity in the inversion of F-region ion-line spectra measured at Arecibo using coded long pulses

The use of coding in incoherent scatter radar (ISR) probing of the F-region ionosphere with long transmitted pulses mitigates the range mixing problem associated with uncoded long pulse (ULP) radar probing in exchange to a reduced signal-to-clutter ratio, limiting the usefulness of this coded long pulse (CLP) technique to relatively low F-region heights. This CLP technique enables the estimation of range localized scattered signal spectra that can be fitted to height specific ISR model spectra in order to estimate the ionospheric state parameters controlling the spectral models. The well-known parameter ambiguity problem — different ionospheric parameter combinations can result in similar spectral shapes — is the major challenge in this fitting process particularly at ranges returning weaker scattered signals. We present here an improved mitigation strategy in CLP spectral fitting in the presence of ion-temperature/composition ambiguity developed with insights derived from a landscaping study of the multi-dimensional parameter space relevant to F-region scattering. The new inversion strategy is applied to the Sept 23-26, 2016, CLP dataset from Arecibo Observatory and the inversion results are compared with ULP inversions for the same time period and the Madrigal regional model for Arecibo. A companion paper describes joint full-profile inversions of the CLP and ULP spectra with initial guesses for lower F-region heights obtained from CLP data fitting described here.