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3/3/2016 GEO327G/386G, UT Austin 5-1
The Global Positioning System IIField Experiments
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Mexico DGPS Field Campaign
Cenotes in Tamaulipas, MX, near Aldama
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Are Cenote Water Levels Related?
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DGPS Static Survey of Cenote Water Levels
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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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Determining Orthometric Heights
• Ortho. Height = (H.A.E. – Geoid Height)
Need:
1) Ellipsoid model – GRS80 – NAVD88• reference 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
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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)
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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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Results
• Horizontal accuracies of <1 cm
• Vertical accuracies of 2-5 cm for 4 hrs of data
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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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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200 0 200 400 600
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
Field Hardware
Mobile Devices
Outdoor tablet computers – Windows
Field GIS/GPS Software
ESRI Software
ArcPad
ArcMap
Collector App
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GPS-equipped Windows Mobile Devices
• Small, low res., color screens
• Limited CPU
• Resistive stylus pen
• Up to 12 hrs. battery life
• Light, portable
• Variably rugged
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Outdoor Tablet Computers
• Large, outdoor-viewable,
high res. color screens
• Inductive stylus pen
• 3-4 hr. battery life
• Heavy, rugged
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GIS-GPS Software
ArcPad
Uses standard data formats – shapefile, tif, SID, etc.
Good GPS support
Supports custom forms
Well-integrated with ArcGIS products
Easy to use
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Tablet Running ArcPad
GPS Location
pCcm
pCdmQal
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ArcGIS - ArcMap Software
Desktop software in the field
Powerful Drawing tools – best feature
Edit Geodatabases in the field
Minimal GPS capture tools
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Tablet Running ArcMap
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High-Tech Mapping Tools
Field Hardware
Mobile Phones
Ipad or other tablet
Field GIS/GPS Apps.
Apple OS, Android OS Collector App
Survey123
FieldMove
iGIS
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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”)
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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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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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GPS Equipment
Hand-helds $100-$450 – navigation instruments
Garmin
Magellan
GPS for PDAs
• Way Points collection
• Manual entry into GIS,
no attribute info. stored
• “Differential ready” but
no post-processing
For survey apps.:
+/- ~15 meters
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GPS Equipment
Sub Meter (x, y) Accuracy, Hand-helds: $1000-$5000
Trimble
Ashtech
Topcon
Sokkia
others
Datalogging with “data dictionary” to upload/store attribute info.
GPS signal data collection for later post-processing
Custom RTK and beacon antennae feasible
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GPS Equipment
Geodetic-quality Instruments
• Trimble
• Ashtech
• Sokkia
• Others
Cm – mm in x and y; 2 cm in z
Stationary Antenna
Large memory for continuous data collection
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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?)
SBAS Service Areas
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SBAS = Satellite Based Augmentation SystemsSource: Wikipedia, 2015