Luiz Fernando Antonio Dalbelo (MSc Student)Luiz Fernando Antonio Dalbelo (MSc Student)Daniele Barroca Marra Alves (PhD Student)Daniele Barroca Marra Alves (PhD Student)

Prof. Dr. João Francisco Galera MonicoProf. Dr. João Francisco Galera MonicoProf. Dr. Paulo de Oliveira CamargoProf. Dr. Paulo de Oliveira Camargo

Faculty of Science and Technology (FCT) - São Paulo State University (UNESP)

FCT/UNESP - Pres. Prudente, São Paulo, Brazil

 

BRAZILIAN IONOSPHERIC MODEL APPLIED TO DIFFERENTIAL GPS

FCT/UNESP

CONTENTS OF THE PRESENTATIONCONTENTS OF THE PRESENTATION

Introduction;Introduction;

Basics concept of the Ionospheric Model Basics concept of the Ionospheric Model used (Mod_Ion);used (Mod_Ion);

DGPS and modified DGPS concepts;DGPS and modified DGPS concepts;

Experiments and analysis;Experiments and analysis;

Conclusions.Conclusions.

IntroductionIntroduction A positioning method that has received A positioning method that has received

great attention in the area of navigation is great attention in the area of navigation is the Differential GPS (DGPS). the Differential GPS (DGPS).

This method has been used in several This method has been used in several applications such as: navigation, surveying, applications such as: navigation, surveying, precision agriculture and others. precision agriculture and others.

In the basic concept of DGPS it is assumed a In the basic concept of DGPS it is assumed a high correlation of the errors involved in the high correlation of the errors involved in the base and rover stations.base and rover stations.

IntroductionIntroduction

Therefore, it is possible to generate Therefore, it is possible to generate corrections in the base stations to be corrections in the base stations to be applied in the rover one (pseudorange applied in the rover one (pseudorange observable corrections).observable corrections).

DGPS provides a reasonable accuracy for DGPS provides a reasonable accuracy for short distances.short distances.

However, the accuracy decreases with However, the accuracy decreases with distances growth due to spatial distances growth due to spatial decorrelation of the errors.decorrelation of the errors.

IntroductionIntroduction

Therefore, to obtain a better positioning Therefore, to obtain a better positioning quality, an adequate modeling of these quality, an adequate modeling of these errors is necessary. errors is necessary.

The aim of this presentation is to evaluate The aim of this presentation is to evaluate the performance of the the performance of the Ionospheric Model Ionospheric Model (Mod_Ion) for reducing DGPS errors.(Mod_Ion) for reducing DGPS errors.

Ionospheric ModelIonospheric Model

The Ionospheric model (Mod_Ion) was The Ionospheric model (Mod_Ion) was developed at São Paulo State University developed at São Paulo State University (FCT/UNESP). (FCT/UNESP).

This model uses GPS double frequency data This model uses GPS double frequency data from a regional network of reference stations from a regional network of reference stations to compute the ionospheric parameters using a to compute the ionospheric parameters using a Fourier series.Fourier series.

The model is based on the difference between The model is based on the difference between the two original pseudoranges ( ) or the two original pseudoranges ( ) or pseudoranges filtered by the carrier phase pseudoranges filtered by the carrier phase (CAMARGO, 1999; CAMARGO et al., 2000).(CAMARGO, 1999; CAMARGO et al., 2000).

sr2

sr1 P, P

Mod_IonMod_IonL1 PseudorangeL1 Pseudorange

1p1ps

1psr1

sr

sr1 RSIP

2p2ps

2psr2

sr

sr2 RSIP

21Prp1p2 sp1

sp2

sr1

sr1

sr2 F +] )R - (R + ) S- F[(S + I )P F(P

)ff/(f F 22

21

22

21Prp1p2sp1

sp2

rs

v1s

r1sr2 F +] )R-(R + ) S- [(S F +

)z cos(

I )P F(P

L2 PseudorangeL2 Pseudorange

Equation of observation for the Mod_IonEquation of observation for the Mod_Ion

Ionospheric delay along the path linking the satellite and receptor Ionospheric delay along the path linking the satellite and receptor

Where:Where:

Experiments were carried out during the period Experiments were carried out during the period of maximum solar activity (2000 - 2001) and of maximum solar activity (2000 - 2001) and solar explosions (CAMARGO; MONICO; solar explosions (CAMARGO; MONICO; MATSUOKA and DAL POS, 2001).MATSUOKA and DAL POS, 2001).

To evaluate the Mod_Ion, were computed the To evaluate the Mod_Ion, were computed the discrepancies:discrepancies:

Without Ionospheric Corrections (WoIC)Without Ionospheric Corrections (WoIC) With Ionospheric Corrections (WIC)With Ionospheric Corrections (WIC)

The estimated values were compared daily with The estimated values were compared daily with the “ground truth”.the “ground truth”.

The data series correspond to the four seasons The data series correspond to the four seasons (Winter and Spring / 2000, Summer and Fall / (Winter and Spring / 2000, Summer and Fall / 2001). 2001).

Point Positioning Using Mod_IonPoint Positioning Using Mod_Ion

X Discrepancies (DX)

-6-30369

12

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

WoIC

WIC

Y Discrepancies (DY)

-14-11-8-5-214

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

Z Discrepancies (DZ)

-14

-11

-8

-5

-2

1

4

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

winter / 2000 spring / 2000 summer / 2001 fall / 2001

X Discrepancies (DX)

-6-30369

12

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

WoIC

WIC

Y Discrepancies (DY)

-14-11-8-5-214

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

Z Discrepancies (DZ)

-14

-11

-8

-5

-2

1

4

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

winter / 2000 spring / 2000 summer / 2001 fall / 2001

Point Positioning Using Mod_IonPoint Positioning Using Mod_Ion

UEPP station (Brazil)UEPP station (Brazil)

Resultants (meter)Values Discrepancies

(86.1%)RMS

(64.3%)Precision (1)

(37.8%)WoIC WIC WoIC WIC WoIC WIC

Maximum 19.87 4.46 22.93 10.10 12.91 9.33Minimum 6.97 0.23 8.86 3.27 2.48 2.84Average 14.34 1.82 17.10 6.09 8.81 5.63

Point Positioning Using Mod_IonPoint Positioning Using Mod_Ion

Geometric Height Discrepancies

-9-6-30369

121518

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

winter / 2000 spring / 2000 summer / 2001 fall / 2001

h -

Err

or (

m)

WoIC

WIC

Geometric Height Discrepancies

-9-6-30369

121518

183 184 185 186 187 188 189 275 276 277 278 279 280 281 1 2 3 4 5 6 7 91 92 93 94 95 96 97

winter / 2000 spring / 2000 summer / 2001 fall / 2001

h -

Err

or (

m)

WoIC

WIC

Basic Concept of DGPSBasic Concept of DGPS Pseudorange correctionsPseudorange corrections

c

c

c

Z

Y

X

4

3

2

1

p

p

p

p

Base Station Rover

Station

4

3

2

1

p

p

p

p

Modified Concept of DGPSModified Concept of DGPS Pseudorange and Ionospheric correctionsPseudorange and Ionospheric corrections

4

3

2

1

p

p

p

p

Base Station

Rover Station

4

3

2

1

p

p

p

p

Base Ionospheric corrections

Rover Ionospheric corrections

ExperimentsExperiments

Some DGPS experiments were carried Some DGPS experiments were carried out using Mod_Ion. out using Mod_Ion.

The stations used are from RBMC The stations used are from RBMC (Brazilian Continuous Network of (Brazilian Continuous Network of Monitoring GPS Satellites). Monitoring GPS Satellites).

This stations are: UEPP, PARA, VICO This stations are: UEPP, PARA, VICO and SALV. UEPP was used as base and SALV. UEPP was used as base station, and the others as rover. station, and the others as rover.

ExperimentsExperiments It was processed 22 hours of data on April It was processed 22 hours of data on April

04, 2005.04, 2005.

Baseline Baseline

• UEPP – PARA (430 km);UEPP – PARA (430 km);• UEPP – VICO (897 km);UEPP – VICO (897 km);• UEPP – SALV (1693 km).UEPP – SALV (1693 km).

The results obtained by DGPS and DGPS The results obtained by DGPS and DGPS using Mod_Ion (DGPS+I) were compared with using Mod_Ion (DGPS+I) were compared with the “ground truth” coordinates.the “ground truth” coordinates.

ExperimentsExperiments

The next figures present:The next figures present:

• Horizontal Resulting (HR) for DGPS Horizontal Resulting (HR) for DGPS (HR_DGPS) and for DGPS using Mod_Ion (HR_DGPS) and for DGPS using Mod_Ion (HR_DGPS+I);(HR_DGPS+I);

• Altimetric Resulting (AR) for DGPS Altimetric Resulting (AR) for DGPS (AR_DGPS) and for DGPS using Mod_Ion (AR_DGPS) and for DGPS using Mod_Ion (AR_DGPS+I);(AR_DGPS+I);

Quality Analyses Quality Analyses

UEPP – PARA (430 km)UEPP – PARA (430 km)

Quality Analyses Quality Analyses

UEPP – VICO (897 km)UEPP – VICO (897 km)

Quality Analyses Quality Analyses

UEPP – SALV (UEPP – SALV (16931693 km) km)

Quality Analyses Quality Analyses

(m)

UEPP – PARA (DGPS)UEPP – PARA (DGPS) UEPP – PARA (DGPS+I)UEPP – PARA (DGPS+I)

HR AR R HR AR R

AV 1.933 5.169 5.715 1,819 1.423 2.499

SD 1.410 5.278 5.257 1.636 1.288 1.851

RMS 2.392 7.387 7.765 2.446 1.920 3.110

(m)(m) UEPP – VICO (DGPS)UEPP – VICO (DGPS) UEPP – VICO (DGPS+I)UEPP – VICO (DGPS+I)

HR AR R HR AR R

AV 3.760 2.812 5.050 3.224 2.900 4.634

SD 2.263 2.757 3.045 1.682 2.289 2.324

RMS 4.388 3.938 5.897 3.636 3.694 5.184

(m)(m) UEPP – SALV (DGPS)UEPP – SALV (DGPS) UEPP – SALV (DGPS+I)UEPP – SALV (DGPS+I)

HR AR R HR AR R

AV 5.269 3.418 6.737 3.829 3.045 5.275

SD 2.324 3.373 3.292 1.226 2.915 2.473

RMS 5.759 4.802 7.498 4.021 4.216 5.825

Quality AnalysesQuality Analyses

UEPP-PARA (%)UEPP-PARA (%)

HR AR R

AV 5.863 72.470 56.269

SD -16.036 75.589 64.797

RMS -2.273 74.015 59.952

UEPP-VICO (%)UEPP-VICO (%)

HR AR R

AV 14.252 -3.110 8.230

SD 25.679 16.969 23.688

RMS 17.138 6.191 12.086

UEPP-SALV (%)UEPP-SALV (%)

HR AR R

AV 27.335 10.909 21.709

SD 47.225 13.558 24.892

RMS 30.187 12.205 22.312

Improvements provided by DGPS+I in relation to DGPS.

It is possible to notice that improvements of up to ~60% were obtained.

ConclusionsConclusions

The basic concepts of DGPS and DGPS+I were presented.

It was shown experiments accomplished using different baselines.

One can observe a significant improvement provided by DGPS+I.

In the experiments were noticed improvements for the baseline PPTE-PARA of up to ~60%.

ConclusionsConclusions

For the baselines PPTE-VICO and PPTE-SALV For the baselines PPTE-VICO and PPTE-SALV the improvement were the improvement were of up to ~12% and ~12% and ~22% respectively.~22% respectively.

So, the Mod_Ion may be a good possibility to be used together the DGPS.

Thank you !Thank you !