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HIGARUS 08Solar Disturbance of GPS Satellite Orbits
Merita HaliliOrhan Veliu
06 june 2008
Introduction
HiGarus ’08 -Continuation of previous work
Project goal◦ Effect of high solar activity on:
GPS satellite orbit positions Ground positions
Sun Activity 11 year cycle Number of sunspots 24th cycle
Geomagnetic storms Solar radiation storms Radio blackouts
Solar Storms
Humans in space Satellite operations Aircraft operations Power and communications Climate change
Solar activity affects:
SWPC archive Storms(G3 to G5 and S3 to S5) Calculate and compare
◦ Broadcast and precise satellite orbit positions◦ Broadcast and precise ground positions
Selection of solar storms
Broadcast:o Satellite orbits computed using orbit parameters derived
from ephemerideso Satellite clock error parameterso Correct the pseudoranges for satellite clock erroro Least Square Adjustment to compute receiver position
o Precise:o Precise orbits provided from IGS websiteo Interpolate to required epochso Least Square Adjustment to compute receiver position
Position Determination
GJOV Reference StationConsists of:
o Archive with stored 24/7 raw-data, since July of 2000o GNSS Antennao Two dual-frequency receiverso Two computers, each connected to a receivero Appropriate software applications
Does:o Tracks the number of and the status of all visible satellites and
stores the data transmitted by the satellites.o Displays receiver’s current position and time.o Downloads and stores raw‐data measurementso Transmits the data for “real time” positioning.
Equipment
Software Receiver software
o Geodetic Base Station Software (GBSS)o PC-CDUo tps2rin
Programmingo Microsoft Visual Basic 2005 Express Editiono FreeBasicIDE – Fbide
Othero Word, Excel, Access, Visio, …
Data Formats
Broadcast ephemeriso Binary formato RINEX format (ASCII)
IGS precise orbitso SP3 format (ASCII)
Parameters and Assumptions
Study Analysis Periodo Start/end timeo 24 hours, after the reported end of storm
Sampling Intervalo Five-minute intervalo One-minute intervalo One-second interval
Satellite antenna phase center offset
WGS84 vs. ITRF
Data Processing StepsBroadcast position1. Generate a list of required epochs2. Extract visible satellites/observed pseudo-ranges3. Extract broadcast ephemeris4. Compute broadcast orbit5. Compute broadcast receiver position
Precise position6. Interpolate to epoch of observation7. Compute precise orbit8. Compute precise receiver position
Compare positions9. Compare broadcast and precise orbits10. Compare broadcast and precise receiver positions
Analyze Errors11. Analyze orbit errors12. Analyze receiver position errors
Written Programs Visual Basic 2005 and FreeBasic
o Short programso Comment the source codeo Document program
dependencies
Programs, Process Flowchart
Difficulties Non-standard RINEX Huge amount of data to process Many parameters in the RINEX - files
Results Satellite orbit positions Ground positions
Study periods: Storm day Day after the storm Clear day with no solar activity
Short intervals
Storm Day - 30.10.2003Satellites position 30.10.2003
Difference between broadcast and precise ephemeris on X5 minutes interval from 01:00AM until 11:00PM , UT
06:00PM -09:00 PM (G4)09:00 PM -12:00 AM(G5)
30.10.2003 – 1 minute interval
Satellites position 30.10.2003Difference between broadcast and precise ephemeris on X
1 minute interval from 01:00AM until 11:00PM , UT
30.10.2003 – 1second interval
Satellites position (PRN07)30.10.2003Difference between broadcast and precise ephemeris on X,Y,Z
1 second interval, UT
Storm Day – 08.11.2004Satellites position 08.11.2004.
Difference between broadcast and precise ephemeris on Y5 minutes interval from 01:00AM until 11:00PM , UT
Day after the storm – 09.11.2004
Satellites position 09.11.2004. Difference between broadcast and precise ephemeris on X
5 minutes interval from 01:00AM until 11:00PM , UT
Clear day without stormSatellites position 26.12.2003
Difference between broadcast and precise ephemeris on X1 minute interval from 01:00AM until 11:00PM , UT
Ground position – storm dayGround positions 30.10.2003
Difference between broadcast and precise ephemeris on X .Y, Z1 second interval from 01:00AM until 02:00AM , UT
GPS satellite orbits, during the selected study periods, do not tend to be disturbed by geomagnetic or solar radiation storms.
Conclusions
Detailed study of solar storms Longer study periods Advanced programming Advanced analysis tools Phase pseudo-range measurements Include also other GNSS
Recommendations
For more information visit:http://hovedprosjekter.hig.no/v2008/iia/geo/higarus-08/