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

1. BRAZILIAN IONOSPHERIC MODEL APPLIED TO DIFFERENTIAL GPS Luiz Fernando Antonio Dalbelo (MSc Student) Daniele Barroca Marra Alves (PhD Student) Prof. Dr. João Francisco Galera Monico Prof. Dr. Paulo de Oliveira Camargo Faculty of Science and Technology (FCT) - São Paulo State University (UNESP) FCT/UNESP - Pres. Prudente, São Paulo, Brazil FCT/UNESP

2. CONTENTS OF THE PRESENTATION • Introduction; • Basics concept of the Ionospheric Model used (Mod_Ion); • DGPS and modified DGPS concepts; • Experiments and analysis; • Conclusions.

3. Introduction • A positioning method that has received great attention in the area of navigation is the Differential GPS (DGPS). • This method has been used in several applications such as: navigation, surveying, precision agriculture and others. • In the basic concept of DGPS it is assumed a high correlation of the errors involved in the base and rover stations.

4. Introduction • Therefore, it is possible to generate corrections in the base stations to be applied in the rover one (pseudorange observable corrections). • DGPS provides a reasonable accuracy for short distances. • However, the accuracy decreases with distances growth due to spatial decorrelation of the errors.

5. Introduction • Therefore, to obtain a better positioning quality, an adequate modeling of these errors is necessary. • The aim of this presentation is to evaluate the performance of the Ionospheric Model (Mod_Ion) for reducing DGPS errors.

6. Ionospheric Model • The Ionospheric model (Mod_Ion) was developed at São Paulo State University (FCT/UNESP). • This model uses GPS double frequency data from a regional network of reference stations to compute the ionospheric parameters using a Fourier series. • The model is based on the difference between the two original pseudoranges ( ) or pseudoranges filtered by the carrier phase (CAMARGO, 1999; CAMARGO et al., 2000).

7. Mod_Ion L1 Pseudorange L2 Pseudorange Equation of observation for the Mod_Ion Where: Ionospheric delay along the path linking the satellite and receptor

8. Point Positioning Using Mod_Ion • Experiments were carried out during the period of maximum solar activity (2000 - 2001) and solar explosions (CAMARGO; MONICO; MATSUOKA and DAL POS, 2001). • To evaluate the Mod_Ion, were computed the discrepancies: • Without Ionospheric Corrections (WoIC) • With Ionospheric Corrections (WIC) • The estimated values were compared daily with the “ground truth”. • The data series correspond to the four seasons (Winter and Spring / 2000, Summer and Fall / 2001).

9. Point Positioning Using Mod_Ion UEPP station (Brazil)

10. Point Positioning Using Mod_Ion

11. Pseudorange corrections Basic Concept of DGPS Base Station Rover Station

12. Pseudorange and Ionospheric corrections Modified Concept of DGPS Base Ionospheric corrections Rover Ionosphericcorrections Base Station Rover Station

13. Experiments • Some DGPS experiments were carried out using Mod_Ion. • The stations used are from RBMC (Brazilian Continuous Network of Monitoring GPS Satellites). • This stations are: UEPP, PARA, VICO and SALV. UEPP was used as base station, and the others as rover.

14. Experiments • It was processed 22 hours of data on April 04, 2005. • Baseline • UEPP – PARA (430 km); • UEPP – VICO (897 km); • UEPP – SALV (1693 km). • The results obtained by DGPS and DGPS using Mod_Ion (DGPS+I) were compared with the “ground truth” coordinates.

15. Experiments • The next figures present: • Horizontal Resulting (HR) for DGPS (HR_DGPS) and for DGPS using Mod_Ion (HR_DGPS+I); • Altimetric Resulting (AR) for DGPS (AR_DGPS) and for DGPS using Mod_Ion (AR_DGPS+I);

16. Figura 2: Estações da RBMC utilizadas nos experimento. Quality Analyses • UEPP – PARA (430 km)

17. Figura 2: Estações da RBMC utilizadas nos experimento. Quality Analyses • UEPP – VICO (897 km)

18. Figura 2: Estações da RBMC utilizadas nos experimento. Quality Analyses • UEPP – SALV (1693 km)

19. Figura 2: Estações da RBMC utilizadas nos experimento. Quality Analyses

20. Quality Analyses Improvements provided by DGPS+I in relation to DGPS. It is possible to notice that improvements of up to ~60% were obtained.

21. Conclusions • 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%.

22. Conclusions • For the baselines PPTE-VICO and PPTE-SALV the improvement were of up to~12% and ~22% respectively. • So, the Mod_Ion may be a good possibility to be used together the DGPS.

23. Thank you !