The Global Positioning System II Field Experiments

Geo327G/386G: GIS & GPS Applications in Earth Sciences Jackson School of Geosciences, University of Texas at Austin 10/8/2020 5-1 Mexico DGPS Field Campaign Cenotes in Tamaulipas, MX, near Aldama

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-2 Are Cenote Water Levels Related?

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-3 DGPS Static Survey of Cenote Water Levels

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-4 Determining Orthometric Heights

❑Ortho. Height = H.A.E. – Geoid Height

Height above MSL (Orthometric height) H.A.E.

Geoid height Earth Surface = H.A.E.

Geoid

Ellipsoid Geoid Height Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-5 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

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-6 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)

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-7 Static Carrier-phase solutions obtained by:

❑Commercial post-processing software ❑e.g. Trimble Pathfinder office ❑Web-based Precise Point Position Services ❑SCOUT – Scripps, UCSB - global ❑OPUS – NGS (US and territories) ❑All services require files in RINEX format

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-8 Results

❑Horizontal accuracies of <1 cm ❑Vertical accuracies of 2-5 cm for 4 hrs of data

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-9 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)

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at 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

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-11 Low-Tech Mapping

◼ Gridded maps/photos, pencil, GPS receiver

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MN UTM NAD83 13N 200 0 200 400 600 Spence 7.5 ' Quad. Meters True N is ~1 degrees East of grid N. 1:12,002 16 degrees Contour Interval = 20 feet Õ

10/8/2020 12 High-Tech Mapping Tools Mobile GIS Apps

◼ PDF Maps ($)

◼ iGIS

◼ Collector

◼ QGIS

◼ GIS Pro ($)

◼ Field Move

10/8/2020 22 High-Tech Mapping Tools

◼ App Distinctions

 Will it accept custom georeferenced maps? (geotifs, shapefiles, PDFs)  Will 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 $$

10/8/2020 23 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; 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”)

10/8/2020 5-24 Receiver attributes

❑# of Channels ❑ Data Storage ❑One channel required for each ❑ Way-points vs. data logging frequency (L1, +/- L2) ❑ Positions vs. raw data ❑8 minimum (4 SVs); 12 or more ❑ Data upload & download desirable ❑ Data dictionary upload for storing ❑Antenna positions by attributes (pt., line, ❑Remote, fixed area) ❑Power source ❑Internal, external

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-25 Receiver attributes

❑DGPS capable ❑ Ionosphere Correction or ❑Beacon antenna for real-time model DGPS ❑ Dual channel vs. single channel ❑Download and post-process receiver ❑ Troposphere model? ❑WAAS capable

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-26 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?)

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-30 SBAS Service Areas

Source: Wikipedia, 2015 SBAS = Satellite Based Augmentation Systems

Geo327G/386G: GIS & GPS Applications in Earth Sciences 10/8/2020 Jackson School of Geosciences, University of Texas at Austin 5-31