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
URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Setting the scene: Ionosphere occultation principleSetting the scene: Ionosphere occultation principle
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
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
URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Occultation geometryOccultation geometry
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)
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
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
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
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
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
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
URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Ørsted estimated TEC residuals, April 18 1999Ørsted estimated TEC residuals, April 18 1999
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( )
URSI XXVI General Assembly, Toronto, Canada, 13-21 August 1999
Simulated TEC residuals, spherical asymmetry conditionsSimulated TEC residuals, spherical asymmetry conditions
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
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