What is GPS? What is GPS?

8/14/2019 What is GPS? What is GPS?

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What is GPS?What is GPS?

GPS, which stands for Global Positioning

System, is the only system today able to

show you your exact position on the Earth

anytime, in any weather, anywhere.

The three parts of GPS are:

Satellites

Receivers

Software


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SatellitesSatellites

There are quite a numberof satellites out there inspace. They are used fora wide range ofpurposes: satellite TV,cellular phones, militarypurposes and etc.Satellites can also be

used by GPS receivers.


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GPS SatellitesGPS Satellites

The GPS OperationalConstellation consists of24 satellites that orbit the

Earth in very preciseorbits twice a day. GPSsatellites emit continuousnavigation signals.


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Receivers and SatellitesReceivers and Satellites

GPS units are made tocommunicate withGPS satellites (whichhave a much betterview of the Earth) tofind out exactly wherethey are on the globalscale of things.


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GPS SignalsGPS Signals

Each GPS satellite transmitsdata that indicates itslocation and the currenttime. All GPS satellites

synchronize operations sothat these repeating signalsare transmitted at the sameinstant.

Physically the signal is

just a complicateddigital code, or in other

words, a complicated

sequence of on and

off pulses.


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Time DifferenceTime Difference

The GPS receiver

compares the time a

signal was transmitted

by a satellite with the

time it was received. The

time difference tells the

GPS receiver how faraway the satellite is.


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Calculating DistanceCalculating Distance

Radio waves travel at the speed of light, roughly 186,000miles per second (mps)

If it took 0.06 seconds to receive a signaltransmitted by a satellite floating directly

overhead, use this formula to find your distance

from the satellite.

186,000 mps x 0.06 seconds = 11,160 miles


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TriangulationTriangulation

Geometric Principle:

You can find one location ifyou know its distance fromother, already-knownlocations.


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3-D Trilateration3-D Trilateration

1 Satellite 2 Satellites

3 Satellites


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Atomic ClocksAtomic Clocks

GPS satellites use Atomic Clocks

for accuracy, but because of the

expense, most GPS receivers do

not.


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Light RefractionLight Refraction

Sometimes the GPSsignal from thesatellite doesnt follow

a straight line.

Refraction is thebending of light as it

travels through onemedia to another.


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Signal RefractionSignal Refraction

Signals from satellites can be like light.

When they hit some interference (air

patterns in the atmosphere, uneven

geography, etc.) they sometimes bend alittle.


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Signal InterferenceSignal Interference

Sometimes the

signals bounce off

things before theyhit the receivers.


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Satellite DistributionSatellite Distribution

When the satellites are all in the same

part of the sky, readings will be less

accurate.


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PDOPPDOP

All of this

combines to makethe signal less

accurate, and

gives it what we

call a high

PDOP.

PDOP = Positional Dilution of Precision

11,000 miles

11,000 miles

11,000 miles

11,000 miles

A PDOP of 8 is poor


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Differential CorrectionDifferential Correction

Differential correction is atechnique that greatlyincreases the accuracy of thecollected GPS data. It

involves using a receiver at aknown location - the "basestation- and comparing thatdata with GPS positionscollected from unknown

locations with "rovingreceivers."

ISU Base Station - http://134.50.65.125/


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Postprocessing / Real-timePostprocessing / Real-time

Before

After


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In a NutshellIn a Nutshell


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Latitude and LongitudeLatitude and Longitude

Latitude and Longitude arespherical coordinates on thesurface of the earth. Latitude

is measured North or Southof the Equator. Longitude ismeasured East or West ofGreenwich. GPS usesLatitudes and Longitudes to

reference locations.


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WaypointsWaypoints

Waypoints are locations or landmarks that can

be stored in your GPS. Waypoints may be

defined and stored in the unit manually by

inputting latitude and longitude from a map orother reference.

Latitude and

Longitude

Your

location

Direction

ofwaypoint

Date

and

Tim

e

Waypoint

Or more usually,waypoints may be

entered directly by takinga reading with the unit atthe location itself, givingit a name, and then

saving the point.


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Data DictionaryData Dictionary

GPS units collect data in:

Points

Lines

Areas

These are called features.A data dictionary is a meansby which we collect specificinformation about a datafeature.
http://www.ianr.unl.edu/pubs/weeds/graphics/spurge2a.jpg


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Roving FileRoving File

A roving file is like

a drawer of a filing

cabinet containingmany feature files.

Collect all the features collected in one interval

in one roving file.


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GPS UsesGPS Uses

Police and

Emergency

MedicalServices

Firefighters

Map makers

Science


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QuestionsQuestions

Alana Jensen

ESER Program

S. M. Stoller Corp.

1780 First Street

Idaho Falls, ID

208-525-9358

[email protected]
mailto:[email protected]://www.stoller-eser.com/sagebrush_steppe.htmhttp://www.stoller-eser.com/sagebrush_steppe.htmmailto:[email protected]

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What is GPS? What is GPS?