Improved Method for Measuring the Satellite-to-Satellite TEC in the Ionosphere by S. Syndergaard
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Improved Method for Measuring the Improved Method for Measuring the Satellite-to-Satellite TEC in the IonosphereSatellite-to-Satellite TEC in the Ionosphere
byby
S. SyndergaardS. SyndergaardH.-H. Benzon H.-H. Benzon G. B. LarsenG. B. Larsen
M. B. Sørensen M. B. Sørensen P. Høeg P. Høeg
Atmosphere Ionosphere Remote Sensing DivisionAtmosphere Ionosphere Remote Sensing DivisionDanish Meteorological InstituteDanish Meteorological Institute
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Setting the scene: Ionosphere occultation principleSetting the scene: Ionosphere occultation principle
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Ionosphere tomography combining ground Ionosphere tomography combining ground and space measurementsand space measurements
Convenient toassume straight lines
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
GPS observables and traditional TEC measureGPS observables and traditional TEC measure
Disregarding troposphere, clocks & ambiguity bias:
1
21
1 )1( dsNfCL e
2
22
2 )1( dsNfCL e
2112 LLTEC
• On occultation links the traditional measure is not exactly the straight line TEC
• Discrepancy becomes appreciable for large electron density gradients
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Occultation geometryOccultation geometry
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
S-S TEC with first order dispersion correctionS-S TEC with first order dispersion correction
2
22
121
12011
ffCTECTEC
w h e r e
da
dsNda
daTECd
sss eGL
22
0
)(
• Mainly proportional to the square of vertical TEC gradients• Accuracy depends on validity of spherical symmetry assumption
(“major” term) (“minor” term)
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Simulated TEC residuals, double Chapman layersSimulated TEC residuals, double Chapman layers
E-layer:Max. dens.: 2·1011 m-3
Scale height: 5 km
F-layer:Max. dens.: 3·1012 m-3
Scale height: 60 km
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
GPS/MET ionosphere profile, occ. 641, Feb 20 1997GPS/MET ionosphere profile, occ. 641, Feb 20 1997
Local time: 12:30Latitude: 36 NLongitude: 144 ESolar flux: 73
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
GPS/MET TEC profile, occ. 641, Feb 20 1997GPS/MET TEC profile, occ. 641, Feb 20 1997
Local time: 12:30Latitude: 36 NLongitude: 144 ESolar flux: 73
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
GPS/MET estimated TEC residuals, occ. 641, Feb 20 1997GPS/MET estimated TEC residuals, occ. 641, Feb 20 1997
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Ørsted ionosphere profile, April 18 1999Ørsted ionosphere profile, April 18 1999
Local time: 14:45Latitude: 33 SLongitude: 13 WSolar flux: 113
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Ørsted TEC profile, April 18 1999Ørsted TEC profile, April 18 1999
Local time: 14:45Latitude: 33 SLongitude: 13 WSolar flux: 113
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Ørsted estimated TEC residuals, April 18 1999Ørsted estimated TEC residuals, April 18 1999
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Alternative estimate of straight line S-S TECAlternative estimate of straight line S-S TEC
)()(
)( 0122
21
0221
22
22
21
22
21
0 sLffsL
ff
ffCffTEC
2122
21
22
21
12 )(LL
ffCffTEC
• Corrects for first order dispersion effects• Not sensitive to spherical asymmetry• Drawback: clocks and POD needs to be solved (removed)
traditional combinationfor comparison( )
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Simulated TEC residuals, spherical asymmetry conditionsSimulated TEC residuals, spherical asymmetry conditions
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URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
SummarySummary
• Satellite-to-satellite TEC L1 - L2 may give TEC errors of order 10 TECU
• Not a big problem at low solar activity or night time (error < 1 TECU)
• May be a problem at day time, solar maximum
• Dispersion correction reduce errors depending on spherical symmetry assumption
• Alternative dual frequency combination can be applied, but then one needs to solve for clocks and POD
• Results can be used in ionosphere tomography to obtain more accurate straight-line satellite-to-satellite TEC