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 10/8/2020 ◼ Gridded maps/photos, receiver pencil, GPS Low - Tech Mapping Tech 900900 000000 100100 200200 300300 400400 500500 600600 700700 800800 900900 000000 100100 200200 300300 400400 500500 600600 700700 800800 719 719 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 720 721 721 721 721 721 721 721 721 721 721 721 721 721 721 721 721 721 721 4949600 4949500 4949400 4949300 4949200 4949100 4949000 4948900 4948800 4948700 4948600 4948500 4948400 4948300 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 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.