The Global Positioning Sytem II 10/8/2020

(1)

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

The Global Positioning System II

Field Experiments

10/8/2020 5-1

Mexico DGPS Field Campaign

Cenotes in Tamaulipas, MX, near Aldama

10/8/2020 5-2

Are Cenote Water Levels Related?

10/8/2020 5-3

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

10/8/2020 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

10/8/2020 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)

10/8/2020 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

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Results

❑

Horizontal accuracies of <1 cm

❑

Vertical accuracies of 2-5 cm for 4 hrs

of data

10/8/2020 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)

10/8/2020 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

10/8/2020 5-11

Low-Tech Mapping

◼

Gridded maps/photos, pencil, GPS receiver

71 99 00 72 0000 72 0100 72 0200 72 0300 72 04 00 72 0500 72 0600 72 0700 72 0800 72 0900 72 1000 72 11 00 72 1200 72 1300 72 1400 72 1500 72 16 00 72 1700 72 1800 4948300 4948400 4948500 4948600 4948700 4948800 4948900 4949000 4949100 4949200 4949300 4949400 4949500 4949600 71 99 00 72 0000 72 0100 72 0200 72 0300 72 04 00 72 0500 72 0600 72 0700 72 0800 72 0900 72 1000 72 11 00 72 1200 72 1300 72 1400 72 1500 72 16 00 72 1700 72 1800 4948300 4948400 4948500 4948600 4948700 4948800 4948900 4949000 4949100 4949200 4949300 4949400 4949500 4949600 200 0 200 400 600 Meters Contour Interval = 20 feet UTM NAD83 13N Spence 7.5 ' Quad.

Õ

16 degrees True N is ~1 degrees East of grid N. 1:12,002 MN

10/8/2020

12

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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

Geo327G/386G:

GIS & GPS Applications in Earth Sciences Jackson School of Geosciences, University of Texas at Austin

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?

10/8/2020 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?)

10/8/2020 5-30

SBAS Service Areas

SBAS = Satellite Based Augmentation Systems

Source: Wikipedia, 2015