# Performance Evaluation of Troposphere Estimated from Galileo-Only Multi-Frequency Observations

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## Abstract

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## 1. Introduction

## 2. GNSS Troposphere Estimation Methods

#### 2.1. Functional Model

#### 2.2. Processing Strategies

## 3. Status of Standalone Galileo Troposphere Solution

## 4. Evaluation of Troposphere Estimated from Multi-Frequency Galileo Observations

#### 4.1. Comparison of ZTD from the IF and the RAW Model

#### 4.2. Comparison of Tropospheric Delay from the GPS-Only and Galileo-Only Solutions

#### 4.3. Multi-Frequency Troposphere Solutions

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Change of the Galileo constellation: Colors indicates the percentage of navigation records in a day providing a healthy Signal-In-Space status, i.e., all healthy = 100% and all unhealthy = 0%.

**Figure 2.**Availability of the Galileo Position Dilution Of Precision (PDOP)< 6 in January (left) and March (right), 2019.

**Figure 3.**Variations of Galileo troposphere ZTDs for stations ZIM2 (top) and GOP6 (bottom) from October 27, 2018 (Day Of Year (DOY) 300), to May 30, 2019 (DOY 150).

**Figure 4.**Standard deviation of the GPS, GLONASS (GLO) and Galileo (GAL) standalone Zenith Total Delay (ZTD) solutions with respect to the multi-GNSS solution. Dark color box is from data before 2019-02-11 and light color after that day.

**Figure 6.**Time series of the difference between ZTDs, as obtained with ionosphere-free (IF) and raw (RAW) models.

**Figure 9.**ZTD evaluation with respect to the IGS final product-bias (top) and standard deviation (bottom).

**Figure 10.**Time series of ZWD (top), North component (middle), and East component (bottom) of the troposphere horizontal gradient obtained with GPS and Galileo IF solutions at the AREG station.

**Figure 11.**Standard deviation of ZTD estimated with Galileo-only observations and different processing strategies.

**Table 1.**Processing strategies for the multi-GNSS (Global Navigation Satellite System) troposphere estimation.

Item | Strategies |
---|---|

Estimator | Forward Kalman/Backward smoothing |

Satellite orbits | Fixed |

Satellite clock offsets | Fixed |

Observations | Carrier phase and pseudorange observations |

Observation weighting | Elevation-dependent weight |

Elevation mask angle | 5 degree |

Station displacement | Solid Earth tides, ocean tide loading, IERS Convention 2010 |

Earth rotation parameters | Fixed |

Antenna phase centers | Corrected with “igs14_ wwww.atx” file |

Zenith Tropospheric Delay | ZHD: Saastamoinen model ZWD: estimated with random-walk Mapping function: GMF |

Tropospheric gradients | Estimated, epoch-wise random-walk |

Phase-windup effect | Corrected |

Receiver clock offset | Estimated as white noise |

Inter-system Bias(ISB) and Inter-frequency Bias(IFB) | Estimated as constant with GPS as a reference |

Station coordinates | Static: estimated and modeled as constants |

Initial phase ambiguities | Estimated as constants in a float solution |

**Table 2.**List of the stations that the receiver satellite antenna phase center offsets (PCOs) and variations (PCVs) are not calibrated with the strategy “GAL-IF1”.

Station Name | Antenna Type |
---|---|

MADR | AOAD/M_T NONE |

SFER | LEIAR25 NONE |

REUN | TRM55971.00 NONE |

Modes | GPS | GAL |
---|---|---|

IF-dual | L1, L2 | E1, E5a |

RAW-dual | L1, L2 | E1, E5a |

RAW-multi | L1, L2, L5 | E1, E5a, E5b, E5 |

GAL | GPS | ||
---|---|---|---|

Observations | Noise [m] | Observations | Noise [m] |

IF | 0.85 | IF | 1.19 |

E1 | 0.31 | L1, | 0.38 |

E5a | 0.45 | L2 | 0.36 |

E5b | 0.46 | L5 | 0.43 |

E5 | 0.15 |

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**MDPI and ACS Style**

Zhao, L.; Václavovic, P.; Douša, J. Performance Evaluation of Troposphere Estimated from Galileo-Only Multi-Frequency Observations. *Remote Sens.* **2020**, *12*, 373.
https://doi.org/10.3390/rs12030373

**AMA Style**

Zhao L, Václavovic P, Douša J. Performance Evaluation of Troposphere Estimated from Galileo-Only Multi-Frequency Observations. *Remote Sensing*. 2020; 12(3):373.
https://doi.org/10.3390/rs12030373

**Chicago/Turabian Style**

Zhao, Lewen, Pavel Václavovic, and Jan Douša. 2020. "Performance Evaluation of Troposphere Estimated from Galileo-Only Multi-Frequency Observations" *Remote Sensing* 12, no. 3: 373.
https://doi.org/10.3390/rs12030373