Perils of the GPS phase scintillation index (σ_ϕ)

Abstract

The phase scintillation index (σϕ), equal to the standard deviation of measured phase, is often used to characterize Global Positioning System (GPS) observations in ionospheric environments that may be scintillated. Since σϕ is dominated by large‐scale fluctuations, questions of usage and interpretation exist as will be illustrated here. Beyond traditional concerns with detrending, multipath and receiver phase noise, there are at least two issues to be considered. The first is the marginal suitability of σϕ to characterize a power law phase screen with a poorly defined low‐frequency component (e.g., outer scale). Second, observed σϕ parameters may not be relevant to GPS receiver tracking impacts. These arguments are outlined here in greater detail and are illustrated with simple one‐dimensional phase screen propagation modeling results. The conclusion is that GPS σϕ values depend critically on the circumstances of measurement and are difficult to compare among observations without additional knowledge, particularly of relative ionospheric drift and irregularity orientation, that may not be available from an isolated GPS receiver. The development of suitable alternative measures requires careful consideration of the elements of GPS scintillation and its impacts. The broader GPS scintillation community should take an active role in developing suitable replacement measures for σϕ.

Statistics of GPS ionospheric scintillation and irregularities over polar regions at solar minimum

“…However, the phase scintillation is dominated by large-scale irregularity (Basu et al 1999). The irregularity in anisotropy and the drift of the irregularity also impact the index (Beach 2006). During the period of Oct 4, 2007, no solar flare (X-ray and EUV radiation) event was observed.…”

“…Although these scintillation indices have been widely used to monitor and measure the intensity of scintillation, one should keep in mind that the derivation of the phase scintillation index r / has many problems and its interpretation may be doubtful (Beach 2006). A series of experiments were set up to study the effects of cutoff frequency for amplitude and phase filtering (Forte 2005).…”

Improved amplitude- and phase-scintillation indices derived from wavelet detrended high-latitude GPS data

“…As Beach (2006) puts it, there are many inaccuracies associated with r / , which calls for the immediate need of a refined phase-scintillation index for GPS scintillation studies. In this study, we introduce a new scintillation index for wavelet-detrended high-latitude GPS data called the CHAIN phase-scintillation index (r CHAIN ).…”

Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013

“…The general lack of amplitude scintillation (S 4 index) at high latitudes has been attributed to a commonly used filter to detrend high-rate GPS data when amplitude and phase scintillation indices S 4 and σ (Beach, 2006;Forte, 2007) are computed. Different filters and indices have been proposed to alleviate this problem (Forte, 2005;Zhang et al, 2010;Mushini et al, 2012).…”