# Luiz Fernando Antonio Dalbelo (MSc Student) Daniele Barroca Marra Alves (PhD Student) Prof. Dr. João Francisco Galera Monico Prof. Dr. Paulo de Oliveira.

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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 BRAZILIAN IONOSPHERIC MODEL APPLIED TO DIFFERENTIAL GPS FCT/UNESP

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

Introduction A positioning method that has received great attention in the area of navigation is the Differential GPS (DGPS). 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. 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. In the basic concept of DGPS it is assumed a high correlation of the errors involved in the base and rover stations.

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

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

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

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

Experiments were carried out during the period of maximum solar activity (2000 - 2001) and solar explosions (CAMARGO; MONICO; MATSUOKA and DAL POS, 2001). 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: To evaluate the Mod_Ion, were computed the 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 ground truth. 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). The data series correspond to the four seasons (Winter and Spring / 2000, Summer and Fall / 2001). Point Positioning Using Mod_Ion

UEPP station (Brazil)

Point Positioning Using Mod_Ion

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

Modified Concept of DGPS Pseudorange and Ionospheric corrections Pseudorange and Ionospheric corrections Base Station Rover Station Base Ionospheric corrections Rover Ionospheric corrections

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

Experiments It was processed 22 hours of data on April 04, 2005. It was processed 22 hours of data on April 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 using Mod_Ion (DGPS+I) were compared with the ground truth coordinates. The results obtained by DGPS and DGPS using Mod_Ion (DGPS+I) were compared with the ground truth coordinates.

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

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

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

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

Quality Analyses Figura 2: Estações da RBMC utilizadas nos experimento. (m) UEPP – PARA (DGPS) UEPP – PARA (DGPS+I) HRARRHRARR AV1.9335.1695.7151,8191.4232.499 SD1.4105.2785.2571.6361.2881.851 RMS2.3927.3877.7652.4461.9203.110 (m) UEPP – VICO (DGPS) UEPP – VICO (DGPS+I) HRARRHRARR AV3.7602.8125.0503.2242.9004.634 SD2.2632.7573.0451.6822.2892.324 RMS4.3883.9385.8973.6363.6945.184 (m) UEPP – SALV (DGPS) UEPP – SALV (DGPS+I) HRARRHRARR AV5.2693.4186.7373.8293.0455.275 SD2.3243.3733.2921.2262.9152.473 RMS5.7594.8027.4984.0214.2165.825

Quality Analyses UEPP-PARA (%) HR AR R AV5.86372.47056.269 SD-16.03675.58964.797 RMS-2.27374.01559.952 UEPP-VICO (%) HR AR R AV14.252-3.1108.230 SD25.67916.96923.688 RMS17.1386.19112.086 UEPP-SALV (%) HR AR R AV27.33510.90921.709 SD47.22513.55824.892 RMS30.18712.20522.312 Improvements provided by DGPS+I in relation to DGPS. It is possible to notice that improvements of up to ~60% were obtained.

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%.

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

Thank you !

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