10/10/2013 GEO327G/386G, UT Austin 5-1

The Global Positioning System II Field 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

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)

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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

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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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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

Windows CE or PocketPC devices

Outdoor tablet computers – Win XP

Field GIS/GPS Software

ESRI Software

ArcPad

ArcMap

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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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Small, low res., color screens

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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

pCdm Qal

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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

Surveying Apps.

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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”)

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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

• European Union Galileo System (2014)

• Russia - Glonass (presently 9 SVs; 24 by 2007)

• Chinese Beidou System (COMPASS, 2020)

• IRNSS – India (2012)

• Japan - QZSS