GPS

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GPS Satellite Technology

• GIS Digital Information
• INLS 110-111

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Global Positioning System (GPS)

• GPS was developed by the U.S. Department of
  Defense
• It enables positioning of objects on or above the
  earth's surface in absolute measurements
• GPS measurements are obtained in the GPS
  coordinate system World Geodetic System 1984
  (WGS84).

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Positioning

• Positioning - process of gaining information
  about our location.
• different forms - which town, street, house
  number or room. Or in latitude longitude, or in
  meters north east of a false origin, as in a
  grid system.

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Positioning GPS Technology

• Many technologies are available for
  positioning-best known is the US Global
  Positioning System (GPS).
• GPS receivers provide location information as a
  set of coordinates in latitude and longitude
• 24 GPS satellites orbit the Earth, providing
  constant position information to receivers on the
  ground.

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What does GPS do?

• satellites provide constant stream of radio
  signals
• with handheld GPS receiver you can determine your
  position on Earth within a few dozen feet
• can tell you the speed and direction youre
  traveling
• provides accurate time of day

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Primary use....

• To locate position determine direction of
  travel
• vital for civilian ships and aircraft
• hikers
• cars with built-in GPS linked to maps

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GPS Satellite Orbits

• 27 operational on 9/29/1998 24 hrs 2 orbits

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Navstar Constellation 3 parts

• Navigation Signal Timing and Ranging
• radio receivers
• listens to transmissions from 4 satellites 2
  frequencies used to lessen interference
• satellites
• must have a minimum of 24 in orbit to work
• ground-control system
• 5 ground stations control satellites master
  control Air Force Base in Colorado Springs

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4 Satellites needed to capture signal arrival
times

• Measurements estimate 4 quantities
• position in 3 dimensions (X, Y, Z) GPS time (T)

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GPS Master Control

• Monitor Station Network

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GPS Satellite Transmissions

• Two sets of direction/time of day signals
• encrypted signals for military use
• civilian signals intentionally degraded
  w/random errors until May of 2000 accuracy to
  100 meters or worse
• now -- depending on equipment accuracy from 100 m
  to 2 cm

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GPS Control Stations

• source Peter Dana - The Geographers Craft

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Remote Sensing

• technique of collecting information from a
  distance
• includes both satellite and aerial data (digital
  and analogue)
• based on physics electromagnetic (EM) energy

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Properties of Electromagnetic Energy (EM)

• travels at the speed of light (3x108/sec)
• wavelength frequency ( of waves per second
  that pass thru fixed point)
• electromagnetic spectrum (conceptual)
• 6 major divisions (from X ray to TV)
• earth features respond to EM energy
• reflection, transmission, absorption, emission
• atmospheric effects
• absorption (sun), windows (best time), scattering
  (particle interference)

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Electromagnetic Spectrum

• Major divisions
• Xray, UV, visible, infrared, microwave, TV

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Remote sensing operation

• Moving Mirror or Pushbroom collection method
• pixel and IFOV (Instantaneous Field of View)
• sensor system contains detectors, each sensitive
  to certain range of wavelength/band
• digital number in each cell measures intensity of
  energy received from IFOV on ground
• response of earth features varies with wavelength
• several bands result in composite image

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Electromagnetic wave

• Components include a sinusoidal electric wave and
  a similar magnetic wave at right angles, both
  perpendicular to the direction of propagation

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EM and leaf interaction

• Incident
• AAbsorption
• TTransmission
• RReflection
• Eemitted (energy absorbed later transmitted)

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Spectral reflectance

• Typical spectral reflectance (wavelength) curves
  for vegetation, soil, and water

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Types of Resolution

• Spectral resolution
• how many bands in sensor system how wide or
  narrow are each narrow better
• Spatial resolution
• how small an area can be detectedpixel size
  1x1m smallest resolution cars
• Radiometric resolution
• range of reflections captured in IFOV 64, 128,
  256, 1024, 2048 (most popular)
• Temporal resolution
• how frequently satellite passes same area

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Impact of Soil temperature

• Generalized 24 hour radiant temperature
  variations
• for soils and rocks vs. water

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Commonly used Satellite images

• moderate resolution satellites
• SPOT, Landsat
• high resolution satellites
• IKONOS
• meterological satellites
• AVHRR, EOS
• digital aerial photographs
• Digital Ortho Quarter Quads (DOQQs), CASI

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Landstat1 images

• Natural Color Imagery

Color Infrared Imagery
30m pixel images
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SPOT images

• Natural Color Imagery

Color Infrared Imagery
10m pixel images
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Landstat1 vs Spot

• Natural Color Imagery
• Landstat1 30m pixels

Natural Color Imagery SPOT 10m pixels
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Compact Airborne Spectrographic Imager (CASI)

• green/red conifers, i.e. spruce/pine
• bright red deciduous, i.e. aspen
• Color Infrared Image (cii)
• 2m pixels

Natural Color Image 2m pixels Bands 1,4,7
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Aerial image USGS DOQQ

• Color image