Critical analysis of ionogram profile inversions and comparison with incoherent scatter radar profiles

The occurrence of a valley in the electron concentration between the E and F regions of the ionosphere has been a problem in the inversion techniques for obtaining true height electron density profiles from ionograms. In this thesis, many of the existing methods for determining the E-F valley effect and hence the start height of the F-layer have been briefly reviewed. Most of these methods lack the ability to adapt to the ionospheric changes in real time because they were designed to give a fixed statistical representation of the E-F valley. To improve on these methods, data obtained from colocated incoherent scatter radar (ISR) and Digisonde (DGS) are used. Utilizing the information from both instruments provides a new opportunity to design a statistical valley model which will make more use of the ionogram signatures and profile parameters. The resultant valley determination method is more flexible in responding to geographic location as well as solar and ionospheric changes.; Comparisons of electron density profiles and F-region peak heights measured by the collocated ISR and the DGS show that the profiles are in good agreement in winter months. However a systematic difference is observed in the equinox and summer months. The differences observed are discussed in terms of the uncertainties in the E-F valley regions. These results show that while errors introduced by incorrect E-F valley model do contribute to the profile shape in the lower F region profile, the effect of this valley region alone does not explain the overall differences observed in the ISR and DGS profiles in the equinox and summer months.; In this thesis, profile reconstruction based on the Field Line Inter-hemispheric Plasma model (FLIP) are used to obtain a theoretical foundation for understanding the E-F valley region. The knowledge obtained from this analysis are used to better interpret the ISR profiles and identify those parameters measurable in ionograms which can be unambiguously measured and used to identify valley characteristics. To establish a E-F valley model, Arecibo ISR and colocated DGS data are used. ISR measured E-F valley parameters and DGS recorded ionogram parameters are compared. The interrelationship of these parameters are identified and used in the construction of a new valley model. Finally, detailed comparisons between the ISR and DGS profiles as well as profile parameters with different valley models are presented and discussed.