M. Gende, C. Brunini Universidad Nacional de La Plata, Argentina. Improving Single Frequency Positioning Using SIRGAS Ionospheric Products

M. Gende, C. BruniniUniversidad Nacional de La Plata, Argentina.

Improving Single Improving Single Frequency Positioning Frequency Positioning

Using SIRGAS Ionospheric Using SIRGAS Ionospheric ProductsProducts

4 September 2009. Buenos Aires, Argentina.

IAG Scientific Assembly: Geodesy For Planet Earth.

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OutlookOutlook

Goal and motivationsWhy in South America?WorkflowResults for a test bedConclusions



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GoalGoal

Increase precise positioning accuracy for single frequency receivers.



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MotivationMotivation

A large part of the GNSS technology users in Latin American have access only to single frequency receivers.

These receivers can not eliminate the ionospheric bias by combining signals.



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Basic FactsBasic Facts

The ionosphere delay is the main error factor in positioning.This delay can be mitigated with a differencing technique.The technique lose effectiveness as the baseline increases.



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Context in South AmericaContext in South America

Because of the size of the continent, the GNSS continuously operating reference stations (CORS) are usually more than 300 kilometers from each other.Under this condition the relative positioning method is less effective.



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Our proposalOur proposal

Use the CORS network already installed in order to produce ionospheric corrections for single frequency receivers.



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MethodologyMethodology

Determine the slant total electron content (STEC) from dual frequency CORS.Estimate STEC in the place the user is located.Correct the single frequency observations. Process the observations in a regular way.



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11stst step: calculate STEC step: calculate STEC using LPIMusing LPIM

Absolute STEC must be determined. Receiver calibration The estimation is done at the zero difference

level

We assume a thin shell model.



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22ndnd step: Estimate STEC step: Estimate STEC

Estimate STEC For each receiver – satellite observation For each epoch



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33rdrd step: Correct the step: Correct the observationsobservations

We can correct measurements Corrected C/A and Corrected L1

We can generate new measurements Simulated P2 and Simulated L2

The user has a new RINEX file with less ionospheric bias



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44rdrd step: Conventional step: Conventional processingprocessing

Positioning is performed using the software that the user usually uses.

We have extended the CORS – user’s distance.



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EvaluationEvaluation

In the position domain Code and phase Static and cinematic

Comparison Single frequency solution Corrected solution Ion free solution



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Test bedTest bed

10 days, 24 hours. Mid latitude. Non disturbed solar conditions. Distance between GPS receivers 200 to

300 Km.



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Standalone positioningStandalone positioning



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HorizontalHorizontal coordinatescoordinates

C/A code

C/A code + corrections

Ion-free

Delt

a N

ort

h (

mete

rs)

Delta East (meters)



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Vertical componentVertical component

P1 Simulated ion-free Ion-free

Delt

a U

p (

mete

rs)

Local Time (hours)

Differential positioning Differential positioning using codeusing code



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C/A code

C/A code + corrections

Delt

a N

ort

h (

mete

rs)

Delta East (meters)

C/A

C/A + corrections



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C/A C/A corrected

Delt

a U

p (

mete

rs)

Local Time (hours)

Differential positioning Differential positioning using carrier phaseusing carrier phase



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Local Time (hours)

Delta North (meters)

Delta East (meters)

C/A

C/A + corrections

C/A

C/A + corrections




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Local Time (hours)

C/A

C/A + corrections



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ConclusionsConclusions It is possible to:

Mitigate the ionospheric effect on L1.Extend the separation between the user and a

CORS station. When corrections are applied:

The horizontal errors are reduced more than 40%. The vertical errors are reduced almost 60%.

95% of the time the corrected observations present errors below. 1 centimeter for the horizontal coordinates. 10 centimeters for the height.



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Extended utilityExtended utility



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Documents

M. Gende, C. Brunini Universidad Nacional de La Plata, Argentina. Improving Single Frequency Positioning Using SIRGAS Ionospheric Products