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/