Perils of the GPS phase scintillation index (σϕ)
Article first published online: 23 MAY 2006
Copyright 2006 by the American Geophysical Union.
Volume 41, Issue 5, October 2006
How to Cite
2006), Perils of the GPS phase scintillation index (σϕ), Radio Sci., 41, RS5S31, doi:10.1029/2005RS003356.(
- Issue published online: 23 MAY 2006
- Article first published online: 23 MAY 2006
- Manuscript Accepted: 14 FEB 2006
- Manuscript Revised: 26 JAN 2006
- Manuscript Received: 30 AUG 2005
- phase scintillation index;
- phase screen
 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.