1
2	Summary of GPS Errors Typical Error [m] Standard GPS Differential GPS (per satellites) Satellite Clocks 1.5 0 Orbit Errors 2.5 0 Ionosphere 5.0 0.4 Troposphere 0.5 0.2 Receiver Noise 0.3 0.3 Multipath 0.6 0.6 The ionosphere is the largest source of error for Standard GPS and second largest for Differential GPS. http://www.trimble.com/gps/howgps-error2.shtml#3
3
4
5	Electron\Ion Density Profile
6
7	Regional Composition Changes and Ion Density
8
9
10	Ionospheric Corrections Need to model the ionosphere to compute corrections Empirical climatological models: Klobuchar coefficients Physics based numerical models: CTIPe, TIE-GCM Data assimilation schemes: US-TEC, GAIM Models can provide both specification and forecast The ionosphere is highly variable in space and time
11	New Products Gradient Detection OPUS Ionospheric Correction Function
12
13	Background/Rationale NGS was running US-TEC in 3-day latent mode As the space weather agency, SWPC to provide ionospheric correctors Avoid the need to continue to update ionospheric activities at NGS every time SWPC makes an improvement to services SWPC is the natural place for providing the service of characterizing the ionosphere
14	Proposal SWPC to provide a web-based customer application for providing ionospheric correctors from a user specified list of options User submits a RINEX file over a particular interval SWPC either uses “best-available” model to evaluate correctors or user specified model (e.g. US-TEC, GAIM, IRI, rtIRI, ….) Return RINEX file to user with correctors inserted Next version of RINEX format has place for corrector
15	Ionosphere Correction for NGS
16	USTEC Product Current NOAA capability for characterizing the total number of free electrons (TEC) in the ionosphere, with parallel input data streams for reliability Since 2004, a product characterizing the ionospheric TEC over the continental US (CONUS) has been running in real-time at NOAA’s Space Environment Center (SEC) The ionospheric data assimilation model uses a Kalman filter and ingests ground-based GPS data to produce 2-D maps of total electron content over the CONUS Product evolved from a collaboration between SEC and NOAA’s National Geodetic Survey (NGS), National Geophysical Data Center (NGDC), and Forecast Systems Laboratory (FSL)
17	Slant-Path TEC Maps
18	Validation Summary
19	SWPC Ionosphere Goals Improve USTEC CONUS: Specification US-TEC slant path total electron content uncertainty < 2 TECU US-TEC vertical electron content uncertainty < 1 TECU CONUS: Forecast 1 hour forecast as good as specification 3 hour forecast: uncertainty < 3 TEC units 6-12 hour forecasts GPS User Tools Color coded regional maps of ionosphere disturbance Support vendors to produce color coded maps for specific applications
20	Conclusions
21
22
23