On the relationship between the geometrical control of scintillation indices and the data detrending problems observed at high latitudes

B Forte B Forte

doi:10.4401/ag-3051

Abstract

The experimental estimate of radio waves scintillation, caused by plasma density irregularities in the ionosphere, is usually attempted by means of scintillation indices which are essentially standard deviations of stochasticly fluctuating parts of the received radio wave intensity and phase. At high latitudes, provided that the propagation problem may be modelled by means of the weak scattering theory, the typical scintillation indices S4 and σφ de- pend on a geometrical factor which introduces some amplifications on their values. Scintillation indices S4 and σφ measured at auroral latitudes are estimated by means of different boundary detrending conditions and the geo- metrical effect on those detrending conditions is investigated. In the case of the polar Low Earth Orbiting (LEO) satellite links considered here, high phase with low intensity scintillation events do not seem to be related to geo- metrical effects only, but rather to misleading data detrending.

Highlights

The amount of scintillation activity present in radio waves propagating through the upper atmosphere is estimated by means of scintillation indices which measure the stochastic fluctuating components of these electromagnetic radiations
The analysis of the scintillation activity recorded on Tsykada satellites links through the estimate of the classical indices S4 and Sφ, coupled with the new parameter Sφ, clarifies the relationship between the geometrical effect which may control σφ in presence of weak scattering and the detrending effect which may introduce misleading large σφ values, at high latitudes
Enhancements in σφ owing to localised peaks in the geometrical factor G remain evident even after the rescaling produced by the increase in the low frequency boundary of the data detrending process

Summary

Introduction

The amount of scintillation activity present in radio waves propagating through the upper atmosphere is estimated by means of scintillation indices which measure the stochastic fluctuating components of these electromagnetic radiations. The detrending process used in these monitors relies on a fixed low frequency cut-off edge equal to 0.1 Hz, as in the case of beacon satellites based experiments It has been a common and accepted picture that GPS scintillation monitors detect high phase scintillation in the presence of low intensity scintillation at high latitudes, implying that GPS equipment is subject to disturbances in the phase rather than on the intensity of the signals, irrespective of how this may impact the functioning of GPS receivers (Doherty et al, 2000; Pi et al, 2001; Aquino et al, 2007). Some scintillation events measured by means of polar LEO beacon satellites are analysed to explain how the classical phase scintillation index σφ may introduce some troubles in the estimate of the phase scintillation activity on a given satellite link This takes into account possible geometrical effects on σφ and an alternate index for the assessment of phase fluctuations induced by drifting electron density irregularities at ionospheric heights (Forte, 2005)

Experimental data

Discussion

Conclusions