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