The Global Positioning System€¦ · Geo327G/386G: GIS & GPS Applications in Earth Sciences...
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Geo327G/386G: GIS & GPS Applications in Earth Sciences Jackson School of Geosciences, University of Texas at Austin The Global Positioning System II Field Experiments 10/19/2017 5-1
Transcript of The Global Positioning System€¦ · Geo327G/386G: GIS & GPS Applications in Earth Sciences...
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
The Global Positioning System IIField Experiments
10/19/2017 5-1
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Mexico DGPS Field Campaign
Cenotes in Tamaulipas, MX, near Aldama
10/19/2017 5-2
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Are Cenote Water Levels Related?
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
DGPS Static Survey of Cenote Water Levels
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Determining Orthometric Heights
Ortho. Height = H.A.E. – Geoid Height
Earth Surface
Ellipsoid Geoid
Height
Height above MSL
(Orthometric height)H.A.E.
Geoid height
= H.A.E.
Geoid
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Determining Orthometric Heights
Ortho. Height = (H.A.E. – Geoid Height)
Need:
1) Ellipsoid model – GRS80 – NAVD88reference stations: HARN (+ 2 cm), CORS (+ ~2 cm)
2) Geoid model – GEOID99 ( + 5 cm for US)
Procedure: Base receiver at reference station, rover at point of interest
a) measure HAE, apply DGS corrections
b) subtract local Geoid Height
10/19/2017 5-6
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Sources of Error
Geoid error – model less well constrained in areas of few gravity measurement
NAVD88 error – benchmark stability, measurement errors
GPS errors – need precise ephemeri, tropospheric delay model, equipment (antennae should be same for base and rover)
10/19/2017 5-7
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Static Carrier-phase solutions obtained by:
Commercial post-processing software
e.g. Trimble Pathfinder office
Web-based Precise Point Position Services
Automated Gipsy – JPL/NASA - global
SCOUT – Scripps, UCSB - global
OPUS – NGS (US and territories)
All services require files in RINEX format
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Results
Horizontal accuracies of <1 cm
Vertical accuracies of 2-5 cm for 4 hrs of data
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
GPS Applications Today
Surveying – Tectonics, Cadastre, Geodesy
Map Making – georeferencing, field studies
Navigation – vehicles, missiles, robots, etc.
Tracking – people, vehicles, pets
“Geotagging” – apply coordinates to digital data (photos, etc.)
Clock Synchronization (+ 10 ns)
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
GPS and Geologic Mapping
Two techniques:
GPS receiver and separate, gridded paper maps
“Mapping-grade” receiver with mapping software and interactive touch screen
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Low-Tech Mapping
Gridded maps/photos, pencil, GPS receiver
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Meters
Contour Interval = 20 feet
UTM NAD83 13NSpence 7.5 ' Quad. Õ16 degrees
True N is ~1 degreesEast of grid N.
1:12,002
MN
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High-Tech Mapping Tools
Mobile Apps PDF Maps
iGIS
Collector
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High-Tech Mapping Tools
App DistinctionsWill maps work offline?
Will GPS work offline?
Does it drop pins, geotag photos, notes etc.? E.g.
PDFMaps and many others free Apps
Does it allow capture of lines and polygons too? E.g.
iGIS, FieldMove, Collector and a few others; free to
$$
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Assisted GPS (A-GPS)
Mobile Devices with GPS and WiFi or Cellular Service, e.g. LBS (location-based services)-capable phone
1. GPS Almanac provided from Server; TTFFfaster – position found by phone (Mobile Station Assisted: “MSA GPS”)
2. GPS data sent to server, position sent back (Mobile Station Based: “MSB GPS”)
10/19/2017 5-24
Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Receiver attributes
# of Channels
One channel required for each frequency (L1, +/- L2)
8 minimum (4 SVs); 12 or more desirable
Antenna
Remote, fixed
Power source
Internal, external
Data Storage
Way-points vs. data logging
Positions vs. raw data
Data upload & download
Data dictionary upload for storing positions by attributes (pt., line, area)
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Receiver attributes
DGPS capable
Beacon antenna for real-time DGPS
Download and post-process
WAAS capable
Ionosphere Correction or model
Dual channel vs. single channel receiver
Troposphere model?
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
Recent Developments
Hand-held equipment – Field GIS
WAAS, LAAS
Other Global Navigation Satellite Systems (GNSS)
European Union Galileo System (2014) and EGNOS SBAS
Russia - GLONASS (23 SVs) + SBAS services
Chinese BeiDou Navigational System (BDS); 14 SVs, 35 by 2020; +SBAS services)
Regional Satellite Systems
Gagan – India (2012)
Japan –MSAS (QZSS?)
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Geo327G/386G: GIS & GPS Applications in Earth SciencesJackson School of Geosciences, University of Texas at Austin
SBAS Service Areas
SBAS = Satellite Based Augmentation SystemsSource: Wikipedia, 2015
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