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10/10/2013 GEO327G/386G, UT Austin 5-1
The Global Positioning System II Field Experiments
10/10/2013 GEO327G/386G, UT Austin 5-2
Mexico DGPS Field Campaign
Cenotes in Tamaulipas, MX, near Aldama
10/10/2013 GEO327G/386G, UT Austin 5-3
Are Cenote Water Levels Related?
10/10/2013 GEO327G/386G, UT Austin 5-4
DGPS Static Survey of Cenote Water Levels
10/10/2013 GEO327G/386G, UT Austin 5-5
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
10/10/2013 GEO327G/386G, UT Austin 5-6
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
10/10/2013 GEO327G/386G, UT Austin 5-7
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)
10/10/2013 GEO327G/386G, UT Austin 5-8
Static Carrier-phase solutions obtained by:
• Commercial post-processing software
• e.g. Trimble Pathfinder office
• Web-based services
• Automated Gipsy – JPL/NASA - global
• SCOUT – Scripps, UCSB - global
• OPUS – NGS (US and territories)
• All services require files in RINEX format
10/10/2013 GEO327G/386G, UT Austin 5-9
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)
10/10/2013 GEO327G/386G, UT Austin 5-10
GPS and Geologic Mapping
Two techniques:
• GPS receiver and separate, gridded paper maps
• “Mapping-grade” receiver with mapping software and interactive touch screen
10/10/2013 GEO327G/386G, UT Austin 5-11
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
10/10/2013 12 GEO327G/386G, UT Austin
High-Tech Mapping Tools
Field Hardware
Windows CE or PocketPC devices
Outdoor tablet computers – Win XP
Field GIS/GPS Software
ESRI Software
ArcPad
ArcMap
10/10/2013 13 GEO327G/386G, UT Austin
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
10/10/2013 14 GEO327G/386G, UT Austin
Small, low res., color screens
10/10/2013 15 GEO327G/386G, UT Austin
Outdoor Tablet Computers
• Large, outdoor-viewable,
high res. color screens
• Inductive stylus pen
• 3-4 hr. battery life
• Heavy, rugged
10/10/2013 16 GEO327G/386G, UT Austin
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
10/10/2013 17 GEO327G/386G, UT Austin
Tablet Running ArcPad
GPS Location
pCcm
pCdm Qal
10/10/2013 18 GEO327G/386G, UT Austin
ArcGIS - ArcMap Software
Desktop software in the field
Powerful Drawing tools – best feature
Edit Geodatabases in the field
Minimal GPS capture tools
10/10/2013 19 GEO327G/386G, UT Austin
Tablet Running ArcMap
10/10/2013 20 GEO327G/386G, UT Austin
High-Tech Mapping Tools
Field Hardware
Mobile Phones
Ipad or other tablet
Field GIS/GPS Apps.
Apple OS, Android OS
Surveying Apps.
10/10/2013 21 GEO327G/386G, UT Austin
10/10/2013 GEO327G/386G, UT Austin 5-22
Assisted GPS (A-GPS)
Mobile Devices with GPS and WiFi or Cellular Service, e.g. LBS-capable phone
1. GPS Almanac provided from Server; TTFF faster – position found by phone (Mobile Station Assisted: “MSA GPS”)
2. GPS data sent to server, position sent back (Mobile Station Based: “MSB GPS”)
10/10/2013 GEO327G/386G, UT Austin 5-23
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)
10/10/2013 GEO327G/386G, UT Austin 5-24
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?
10/10/2013 GEO327G/386G, UT Austin 5-25
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
10/10/2013 GEO327G/386G, UT Austin 5-26
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
10/10/2013 GEO327G/386G, UT Austin 5-27
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
10/10/2013 GEO327G/386G, UT Austin 5-28
Recent Developments
• Hand-held equipment – Field GIS
• WAAS, LAAS
• European Union Galileo System (2014)
• Russia - Glonass (presently 9 SVs; 24 by 2007)
• Chinese Beidou System (COMPASS, 2020)
• IRNSS – India (2012)
• Japan - QZSS