Ionospheric Correlation Analysis for WAAS:Quiet and Stormy

摘要

Dual-f~equency measurements made with wide arearnGPS reference networks provide extremely precisernand geographically diverse observations of thernionosphere. While these measurements amount tornintegrals along a line of sight, coordinatedrnmeasurements can be brought into a singlernobservation framework for modelling the ionosphere.rnIn WAAS, one this is accomplished with onernsimplifying assumption, namely the thin-shellrnapproximation. While this approximation has somernlimitations it is suitable for many applications, one ofrnwhich is the ionospheric differential correction in thernFederal Aviation Administration's Wide ArearnAugmentation System (WAAS) for GPS. The WAASrnapplication was in fact the motivation for thisrncorrelation analysis. The correlation model directlyrnsupports the ionospheric irregularity detectionrnprocess as part of the WAAS integrity algorithms.rnBeyond WAAS, we feel that both the procedures andrnthe results would be useful to the general ionosphericrncommunity who have a great deal of GPS datarnreadily available or would like to fuse disparate datarnsources together.rnWe give here a description of the measurementrnprocessing for noise and multipath removal via arntriple threaded reference network, the extendedrnadditive model, and its utility in the irregularityrndetector. We present correlation analyses ofrnmeasurements made during both nominal (quiet) andrndisturbed (stormy) ionospheric conditions. Inrnparticular, we address the ionospheric activity thatrnoccurred 6-8 April 2000 and 15-16 July 2000. Thisrndata represents the most extreme conditions yetrnexperienced in the current solar cycle.