The Southern Alberta GPS Network: Ongoing Research

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The Southern Alberta GPS Network Ongoing
Research

• Natalya Nicholson
• June 22, 2004
• NCAR Colloquium
• Atmospheric Remote Sensing Using
• The Global Positioning System

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Outline

• 1. Background
• Global Positioning System
• Signal Propagation in the Neutral Atmosphere
• Model Input
• 2. Tomography Model
• 3. Southern Alberta Network
• 4. Additional Research Applications

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Global Positioning System

• Constellation of at least 27 satellites in 6
  orbital planes
• Orbit at 20,000 km
• Continuously transmit radio signals towards the
  Earth
• L1 1575.42 MHz
• L2 1227.60 MHz

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GPS Range Errors

• Timing Errors
• Satellite Clock
• Receiver Clock
• Orbital Errors
• Ionosphere
• Neutral Atmosphere
• Troposphere
• Stratosphere

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Neutral Atmosphere

• Mixture of dry gases and water vapor
• Affects radio signals propagating through it
• 2 Effects
• Propagation delay
• Hydrostatic (DRY)
• Non-Hydrostatic (WET)
• Ray refraction
• Non-dispersive on L1 and L2 frequencies

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Extract Neutral Atmospheric Delay

• Must Remove
• Ionospheric error Dispersive
• Satellite orbit errors
• Resolve integer number of wavelengths
  (ambiguities) on L1 and L2
• Reference station coordinate errors

• Remaining Errors
• Neutral Atmospheric (Tropospheric) delay
• Additional residual errors
• Multipath and receiver noise

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Model Input Slant Wet Delays
Neutral Atmospheric Delay
WET ? SWD input
DRY
Remove using surface pressure
Water Vapor Distribution (Refractivity)
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Tomography Model

• Model wet refractivity, Nw, using functional
  approach
• Horizontal variation
• Low order expansion in latitude and longitude

• Vertical variation
• Discrete layers with constant parameter values
• (ai i 1 5)

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Southern Alberta Network
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Equipment (1/2)

• GPS Receiver
• Novatel MPC
• Euro4 GPS card
• 16 Gb Hard drive
• Internet/Ethernet interface
• GPS Antenna
• Novatel 600
• Meteorological Sensor
• Paroscientific MET3A
• Pressure
• Temperature
• Relative Humidity

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Equipment (2/2)

• 4. Radiometrics Water Vapor Radiometer
• University of Calgary
• 5. Radiometrics Water Vapor Profiler
• University of Calgary
• Radiosonde/Rawinsonde Launches
• Meteorological Service of
• Canada (MSC) and Canadian Meteorological and
• Oceanographic Society (CMOS)
• TITAN Ground-based
• Weather Radar
• Weather Modification Inc.

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July 2003 Campaign A-GAME

• Rocky Mountain Foothills
• Unique weather patterns due to proximity to
  mountains.
• Rapid storm / severe weather formation.

Storm development in Alberta Foothills
Severe hail storm, July 20, 2003
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Research Applications (1/4)
4-D Water Vapor Distribution Modeling with GPS
Wet refractivity profile at expansion point.
3-D Wet refractivity profile.
40 35 30 25 20 15 10 5 0
Wet Refractivity (mm/km)

• Tomography model augmentation with vertical
  information
• (i.e. WV profiler and occultation measurements)

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Research Applications (2/4)
GPS PWV Validation with Radiosondes
C. Smith, 2003
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Research Applications (3/4)
Position Error Modeling Multi-Reference Station
Approach
J. Raquet, 1997
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Research Applications (4/4)
Soil Moisture and Evapotranspiration
Relationships
C. Valeo
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• Thank You!