Introduction to Global Introduction to Global Positioning Systems Positioning Systems

(GPS)(GPS)

Mark Smith, Assistant Professor/Wildlife Extension Specialist

GPS BasicsGPS Basics

► Satellite navigation Satellite navigation systemsystem

►Maintained by the US Maintained by the US GovernmentGovernment All weatherAll weather 24 hour24 hour WorldwideWorldwide

► Available free to the Available free to the publicpublic

Global Position “System”Global Position “System”►Space segmentSpace segment

24 satellites emitting radio signals24 satellites emitting radio signals

►Control SegmentControl Segment US DODUS DOD

►User SegmentUser Segment Your receiverYour receiver

GPS BasicsGPS Basics► Radio signals sent from Radio signals sent from

orbiting satellites to earthorbiting satellites to earth

► Measures receiver-to-satellite Measures receiver-to-satellite distancedistance How long the signal took to get How long the signal took to get

to your receiverto your receiver Speed of light (186,000 m/s)Speed of light (186,000 m/s) Atomic clocksAtomic clocks

► GPS units receive and convert GPS units receive and convert signals to position, velocity, signals to position, velocity, and time informationand time information

GPS BasicsGPS Basics►What’s in a radio signal?What’s in a radio signal?

Psuedorandom code – identifies the satellitePsuedorandom code – identifies the satellite Ephemeris data – tells where the satellite should Ephemeris data – tells where the satellite should

bebe Almanac data – tells the health of the satelliteAlmanac data – tells the health of the satellite

► Constellation of 24 NAVSTAR earth-orbiting Constellation of 24 NAVSTAR earth-orbiting satellitessatellites

►Need to receive a signal from:Need to receive a signal from: 3 satellites for a 2D position3 satellites for a 2D position 4 satellites for a 3D position4 satellites for a 3D position

Sources of GPS ErrorSources of GPS Error► Satellite availabilitySatellite availability► Satellite geometrySatellite geometry► Ionosphere/troposphere conditionsIonosphere/troposphere conditions► Signal blockage (i.e., forest canopy, tall Signal blockage (i.e., forest canopy, tall

buildings)buildings)►Multi-path (signal bounce)Multi-path (signal bounce)► Clock error (timing)Clock error (timing)► Intentional degradation (the old Selective Intentional degradation (the old Selective

Availability)Availability)

Overcoming Overcoming somesome forms of GPS forms of GPS errorerror

► Differential correctionDifferential correction Real timeReal time Post-processingPost-processing ““Base” station at a known location recording satellite Base” station at a known location recording satellite

signals simultaneouslysignals simultaneously Differences in timing are then applied to the signals you Differences in timing are then applied to the signals you

recorded with your receiverrecorded with your receiver

► WAAS enable unitsWAAS enable units Wide Area Augmentation SystemWide Area Augmentation System Modified GPS signal---with error correction factorModified GPS signal---with error correction factor North America onlyNorth America only 25 ground reference stations that collect signals and then 25 ground reference stations that collect signals and then

send correction info to satellites which gets sent to your send correction info to satellites which gets sent to your receiverreceiver

Measures of Position Measures of Position AccuracryAccuracry

►DOP – Dilution of PrecisionDOP – Dilution of Precision Indicator of the quality of the satellite Indicator of the quality of the satellite

constellationconstellation Lower is betterLower is better

Types of DOPTypes of DOP PDOP – Position Dilution of PrecisionPDOP – Position Dilution of Precision VDOP – Vertical Dilution of PrecisionVDOP – Vertical Dilution of Precision HDOP – Horizontal Dilution of PrecisionHDOP – Horizontal Dilution of Precision

Coordinate SystemsCoordinate Systems► Latitude/LongitudeLatitude/Longitude

Degrees, minutes, seconds (33Degrees, minutes, seconds (33oo 14’ 32”) 14’ 32”) Decimal degrees (33.242222Decimal degrees (33.242222oo))

► ProjectionsProjections How “3D” objects are converted to “2D” objectsHow “3D” objects are converted to “2D” objects Cylindrical, Conical, and PlanarCylindrical, Conical, and Planar

► DatumsDatums How the earth is shapedHow the earth is shaped Based on mathematical models of the earth’s shape and Based on mathematical models of the earth’s shape and

dimensionsdimensions

► Universal Transverse Mercator (UTM)Universal Transverse Mercator (UTM) CylindricalCylindrical 60 6-degree slices60 6-degree slices MetersMeters

► Example: UTM, Zone 16N, NAD-27Example: UTM, Zone 16N, NAD-27

UTM ZonesUTM Zones

Which GPS Receiver is Best?Which GPS Receiver is Best?►DeluxeDeluxe

Survey grade unitsSurvey grade units►Used for highway and engineering projectsUsed for highway and engineering projects►Horizontal accuracy within a centimeterHorizontal accuracy within a centimeter►Costs up to $40,000Costs up to $40,000

Mapping/resource grade unitsMapping/resource grade units►Used for mapping roads, stand boundaries, and point Used for mapping roads, stand boundaries, and point

datadata►Relocating data that is not flagged or markedRelocating data that is not flagged or marked►1-5 meter accuracy with good signal1-5 meter accuracy with good signal►Usually requires formal training to useUsually requires formal training to use►Download data to Geographic Information System Download data to Geographic Information System ►Costs begin around $2,000Costs begin around $2,000

Which GPS Receiver is Best?Which GPS Receiver is Best?►EconomicalEconomical

Recreational grade unitsRecreational grade units►General navigation General navigation ►Relocating plots, trees, etc. that have been Relocating plots, trees, etc. that have been

flaggedflagged►Estimating acreage of forest standsEstimating acreage of forest stands►3-5 meter accuracy with good signal3-5 meter accuracy with good signal►Easy to learn using manualEasy to learn using manual►Costs $100 - $500Costs $100 - $500

Which GPS Receiver is Best?Which GPS Receiver is Best?

►Grade GPS you choose depends on Grade GPS you choose depends on field work and data collection needsfield work and data collection needs Recreational grade – most forest Recreational grade – most forest

inventory tasksinventory tasks Resource/mapping grade- determining Resource/mapping grade- determining

harvest boundaries harvest boundaries Recreational grade are good for first-time Recreational grade are good for first-time

GPS users GPS users

GPS in ForestryGPS in Forestry►NavigationNavigation►Pre-harvest and post-harvest stand Pre-harvest and post-harvest stand

delineationdelineation►Road and landing layoutRoad and landing layout►Acre controlAcre control►Equipment trackingEquipment tracking►Wildlife usesWildlife uses

Stand DelineationStand Delineation

►Estimating acreagesEstimating acreages Tree plantingTree planting Herbicide applicationHerbicide application Slope/aspectSlope/aspect

WildlifeWildlife

►GPS collarsGPS collars Large mammalsLarge mammals WaterfowlWaterfowl

155 gm

760 gm

350 gm 1,100 gm

Questions/DiscussionQuestions/Discussion