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Using Signals Emitted by Global Navigation
Satellite Systems
PhD. Thesis submitted for the Degree of Doctor in Sciences Co-Promotors: Carine Bruyninx and Pascale Defraigne
Université Catholique de Louvain – Royal Observatory of Belgium
Eric Pottiaux
Context of the Thesis
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Water Vapour Weather Forecast
Lack of Information about the
Humidity Field
Global Navigation
Satellite Systems
Context of the Thesis
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Provide a Product for Operational Weather Forecast
Study and Observe the Neutral Atmosphere (troposphere)
GNSS Signals
On the courtesy of VTM
INTRODUCTION
Global Navigation Satellite Systems (GNSS)
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GNSS | A Service to Real-time Positioning and Navigation
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GNSS | System Design & Measurements
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Global navigation Satellite Systems (GNSS) • Satellite constellation (altitude ~26000km) • Emitting radio-signal towards the Earth (codes+carriers) • Recorded by ground receivers and antennas
Real-time Applications & Navigation
Scientific Applications
ATMOSPHERIC REFRACTION
Signal or Noise ?
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The position determination is affected by errors Need to be mitigated to achieve the highest precision possible in the position determination
Ionosphere:
Is a dispersive medium By frequency combination Mitigates its effects
Troposphere (0-80km)
GNSS | Atmospheric Refraction
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Ionosphere (80-1100 km) Acceleration (carrier)
Decelerate
Troposphere:
Is a non-dispersive medium Has for primary effect to change the propagation speed To decelerate the signals (measured distance > theoretical distance)
GNSS-Meteorology | A Simplistic View
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Troposphere (0-80km)
1. If satellite’s position is known 2. If station’s position is known
Expressed in metres or millimetres Typical values (Europe): 2.20m to 2.65m at zenith (sea level) Contains information about the atmospheric water vapour that can be used in meteorology (<20% of the total tropospheric delay)
GNSS-Meteorology | A Simplistic View
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Tropospheric Delay Theoretical
Distance Measured Distance
The Tropospheric Delay in Short…
GNSS-Meteorology | A Simplistic View
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Weather Forecasting and Nowcasting
On the courtesy of RTBF
THESIS OBJECTIVES | GNSS-METEOROLOGY
Weather Forecasting in Europe
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Objectives of the Thesis
To Develop a State-of-the-art Methodology
• For estimating tropospheric delays in near real-time
• For weather forecasting in Europe
To Provide a service to European National Meteorological Services via E-GVAP II
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« The EUMETNET EIG GNSS Water Vapour Program II »
ANALYSIS METHODOLOGY | A 2-STEP PROCESSING
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GNSS-Meteorology | A Simplistic View
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Troposphere (0-80km)
1. If satellite’s position is known (IGS Orbit Products)
2. If station’s position is known (computed)
Methodology |A GNSS observation processing in 2 Steps
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Time Current Day Last 31 Days
1st Step: Post-Processing 2nd Step: Near Real-time Current Hour
Precise Positions Post-Processing Tropospheric Delays
Tropospheric Delays Monitoring & Validation
2nd Step: Tropospheric Delay Estimations 1st Step: Precise Position Determination
➤ Near Real-time Analysis
➤ Coordinates fixing and Tropospheric Delay Estimation
➤ Post-processing Analysis
➤ Precise Coordinates (1.3mm N&E, 4.3mm Up)
Methodology |GNSS Observation Networks
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Network of 220+ stations
IGS Network
EUREF Network
Belgian ROB Network
German GREF Network
Dutch Network
French RGP Network
E-GVAP Super-Sites
Methodology |A GNSS observation processing in 2 Steps
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All GNSS-Meteorology Requirements are Satisfied. (Time Resolution, Spatial resolution, Precision, Accuracy , Latency)
Co
ncl
usi
on
Sensitivity Tests & Optimisations
Methodology
Validation
GNSS-Meteorology Requirements
Precision: 4-5mm & Accuracy: < 2.5 mm)
METHODOLOGY | EUROPEAN WEATHER FORECASTS
The EUMETNET EIG GNSS Water Vapour Program (E-GVAP)
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The EUMETNET EIG GNSS Water Vapour Program
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E-GVAP in Short…
15 member states, including Belgium (RMI)
Fruitful collaboration between meteorologists and geodesists
12 GNSS data analysis centres, including Belgium (ROB)
> 1250 unique sites (+ ~200 new sites/year)
~ 15000 obs./hour ~ 360000 obs./day ~ 1.3 million obs./year
The Observing Network
http://egvap.dmi.dk
Impact Studies
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X. Yan et al., 2009 “A clear positive effect on short-range quantitative precipitation forecasts” Eresmaa, 2009 “The impact appears most positive in regions of Europe where GPS station density is highest”
Operational Assimilation within E-GVAP
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Since 2007, operational assimilation in the NWP models at
The European GNSS-based Water Vapour
Observing Network
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GNSS-based tropospheric delays + pressure & temperature records IWV
On the courtesy of Henrik Vedel, DMI
DENSE NETWORKS OF GNSS STATIONS
Location, extension and movement of fine structures
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Multi-Cellular Thunderstorm | 29th June 2005
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Thunderstorm Case|European regional network
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Dense GNSS Networks | The Belgian Dense Network
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Qualitative Analysis |Weather Radars Images
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Added-value of the dense GNSS networks ? Qualitative comparison wrt. weather radars
OO UTC 12 UTC 24 UTC
Rain
On
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urt
esy
of
Lau
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elo
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MI
Qualitative Analysis |The European Network vs. Dense Network
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BRUS
DENT
DOUR
WARE
MEEU
BREE
EIJS
IWV (mm) - 00 UTC
OO UTC 12 UTC 24 UTC
Water Vapour and Rain
IWV
(mm
)
Qualitative Analysis |The European Network vs. Dense Network
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OO UTC 12 UTC 24 UTC
BRUS
DENT
DOUR
WARE
MEEU
BREE
EIJS
IWV (mm) - 00 UTC
Water Vapour and Rain
IWV
(mm
)
Qualitative Analysis |The European Network vs. Dense Network
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Added-value of the dense network ? Comparison wrt. Weather radar images Better resolution with the Belgian dense network Additional information appears wrt. Weather Radar images
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BRUS
DENT
DOUR
WARE
MEEU BREE
EIJS
IWV (mm) - 00 UTC
IWV (mm) - 00 UTC
Quantitative Analysis |Profiles through the IWV field
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4 profiles through the 2-D field In the direction of the front propagation : differences ~2mm (IWV) 3 other profiles: bigger differences Maximal difference : 5.47mm (IWV) between BRUS-ERPE European network: small structures not visible Amplitude of the small structures: 5 to 6 times what nowcasters want to see
BRUS
BRUS BRUS
DENT
WARE BREE DOUR
BRUS
DENT
DOUR
WARE
MEEU BREE
EIJS
IWV (mm) – 12h30
Dense GNSS Networks |Location and movements of the structures
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The Belgian dense network allow to locate and monitor the movements of the structures
Emerging zone of lower IWV density
Thundery precipitation zones in the north/northeast (radar image)
Zone diameters: 25-35km
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Dense GNSS Networks |Location and movements of the structures
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The Belgian dense network allow to locate and monitor the movements of the structures
Emerging zone of lower IWV density
Thundery precipitation zones in the north/northeast (radar image)
Zone diameters: 25-35km
BRUS
DENT
DOUR
WARE
MEEU BREE
EIJS
OO UTC 12 UTC 24 UTC 5 November 2010 36
IWV (mm) – 13h30
CONCLUSIONS AND PERSPECTIVES
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Methodology and Objectives | European Level
We developed a methodology to provide near real-time tropospheric delays for weather forecasting in Europe
The methodology satisfies all requirements for numerical weather forecasting and nowcasting applications
The methodology is used to provide an operational service to European meteorologists (E-GVAP)
The tropospheric delays provided within E-GVAP enter the operational assimilation process at Météo France and U.K Met Office (more coming this autumn/winter)
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Methodology and Objectives | Local Level
We applied the methodology to study the fine structures in the 2-D water vapour field: – A European network can only render the large-scale
structures in the water vapour field
– The Belgian dense GNSS network allows to reconstruct small-scale structures (~ 20 km) and to monitor their locations and movements
– Significant differences up to 5.5 mm (IWV) could be observed between the 2-D water vapour fields
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Perspectives| Meteorology and Weather Forecast
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Several methodology improvements are possible: – Increase the spatial resolution Include more stations from dense GNSS networks Limitation: the computer power
– Turn the analysis into a Multi-GNSS processing GLONASS and Galileo More observations, better precision, better reliability Access to fine tropospheric structures Limitation: no precise real-time orbits for GLONASS, Galileo not ready yet
To study the applicability of the methodology to climate monitoring (Europe+Antartica)
ELIS
ULUX
Perspectives| Climate Monitoring
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Thank you for your Attention