Abstract

Radio wave absorption in the ionosphere is a function of electron density, collision frequency, radio wave polarisation, magnetic field and radio wave frequency. Several studies have used multi-frequency measurements of cosmic radio noise absorption to determine electron density profiles. Using the framework of statistical inverse problems, we investigated if an electron density altitude profile can be determined by using multi-frequency, dual-polarisation measurements. It was found that the altitude profile cannot be uniquely determined from a complete measurement of radio wave absorption for all frequencies and two polarisation modes. This implies that accurate electron density profile measurements cannot be ascertained using multi-frequency riometer data alone, but that the reconstruction requires a strong additional a priori assumption of the electron density profile, such as a parameterised model for the ionisation source. Nevertheless, the spectral index of the absorption could be used to determine if there is a significant component of hard precipitation that ionises the lower part of the D region, but it is not possible to infer the altitude distribution uniquely with this technique alone.

Highlights

  • Jansky (1933) determined that certain detected radio noise was of cosmic origin, and was associated with the Galaxy, founding a new branch of science — Radio Astronomy

  • One later example built by Little and Leinbach (1959) — the R.I.O.M.E.T.E.R — gave the name “riometer” to this generic class of instrument and the term “riometry” for the measurement of cosmic noise absorption (CNA) by the ionosphere

  • The comparison 35 with the nearby incoherent scatter radar indicated that multi-frequency riometry could determine comparable electron density profiles based on the posteriori probability distribution of two free parameters, based on the least-squares fit between the measured absorption spectrum and the parameterised model

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Summary

Introduction

Jansky (1933) determined that certain detected radio noise was of cosmic origin, and was associated with the Galaxy, founding a new branch of science — Radio Astronomy. The comparison 35 with the nearby incoherent scatter radar indicated that multi-frequency riometry could determine comparable electron density profiles based on the posteriori probability distribution of two free parameters (electron precipitation energy and flux), based on the least-squares fit between the measured absorption spectrum and the parameterised model. A measure of the electron collision frequency, ν, is required For this the results collated by Aggarwal et al (1979, Fig.7) were used and a 70 look-up table was generated and linear interpolation was used for determining intermediate values.

Specification of the forward model
Example electron density profiles
Application of the forward model
Interpretation of the SVD products
Inversion
Inversion of arbitrary functions
Remarks
Findings
Conclusions
Full Text
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