GPS and Remote Sensing

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GPS and Remote Sensing

• Lecture 20
• April 7, 2004

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Why GPS and RS in GIS?

• GPS and remote sensing imagery are primary GIS
  data sources, and are very important GIS data
  sources.
• GPS data creates points (positions), polylines,
  or polygons
• Remote sensing imagery and airphotos are used as
  major basis map in GIS
• Information digitized or classified from imagery
  are GIS layers

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Globe Positioning System (GPS)

• GPS is a Satellite Navigation System
• GPS is funded and controlled by the U. S.
  Department of Defense (DOD). While there are many
  thousands of civil users of GPS world-wide, the
  system was designed for and is operated by the U.
  S. military.
• GPS provides specially coded satellite signals
  that can be processed in a GPS receiver, enabling
  the receiver to compute position, velocity and
  time.
• At least 4 satellites are used to estimate 4
  quantities position in 3-D (X, Y, Z) and GPSing
  time (T)

20,000 km
http//maic.jmu.edu/sic/glossary.htmProjection
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Space Segment

• The nominal GPS Operational Constellation
  consists of 24 satellites that orbit the earth in
  12 hours. There are often more than 24
  operational satellites as new ones are launched
  to replace older satellites. The satellite orbits
  repeat almost the same ground track (as the earth
  turns beneath them) once each day. The orbit
  altitude is such that the satellites repeat the
  same track and configuration over any point
  approximately each 24 hours (4 minutes earlier
  each day). There are six orbital planes, with
  nominally four SVs (Satellite Vehicles) in each,
  equally spaced (60 degrees apart), and inclined
  at about fifty-five degrees with respect to the
  equatorial plane. This constellation provides the
  user with between five and eight SVs visible from
  any point on the earth.

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Control Segment

• The Master Control facility is located at
  Schriever Air Force Base (formerly Falcon AFB) in
  Colorado. These monitor stations measure signals
  from the SVs which are incorporated into orbital
  models for each satellites. The models compute
  precise orbital data (ephemeris) and SV clock
  corrections for each satellite. The Master
  Control station uploads ephemeris and clock data
  to the SVs. The SVs then send subsets of the
  orbital ephemeris data to GPS receivers over
  radio signals.

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User Segment

• The GPS User Segment consists of the GPS
  receivers and the user community. GPS receivers
  convert SV signals into position, velocity, and
  time estimates. GPS receivers are used for
  navigation, positioning, time dissemination, and
  other research.

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Coordinate system and height

• GPS use the WGS 84 as datum
• Various coordinate systems are available for
  chosen
• GPS height (h) refers to ellipsoid surface, so it
  is a little difference from the real topographic
  height (H). the difference is the geoid height
  (N), the approximate Mean Sea Level. Some newer
  GPS units now provide the H by using the equation
  Hh-N (N from a globally defined geoid Geoid99)

H topographic height or orthometric
height h ellipsoid height N geoid height H h
- N
http//www.esri.com/news/arcuser/0703/geoid1of3.ht
ml
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GPS positioning services specified in the Federal
Radionavigation Plan

• PPS (precise positioning service) for US and
  Allied military, US government and civil users.
  Accuracy
• - 22 m Horizontal accuracy
• - 27.7 m vertical accuracy
• - 200 nanosecond time (UTC) accuracy
• SPS (standard positioning service) for civil
  users worldwide without charge or restrictions
• - 100 m Horizontal accuracy
• - 156 m vertical accuracy
• - 340 nanosecond time (UTC) accuracy
• DGPS (differential GPS techniques) correct bias
  errors at one location with measured bias errors
  at a known position. A reference receiver, or
  base station, computes corrections for each
  satellite signal.
• - Differential Code GPS (navigation) 1-10 m
  accuracy
• - Differential Carrier GPS (survey)1 mm to 1
  cm accuracy

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DGPS

• The idea behind differential GPS We have one
  receiver measure the timing errors and then
  provide correction information to the other
  receivers that are roving around. That way
  virtually all errors can be eliminated from the
  system (Because if two receivers are fairly close
  to each other, say within a few hundred
  kilometers, the signals that reach both of them
  will have traveled through virtually the same
  slice of atmosphere, and so will have virtually
  the same errors)
• real time transmission DGPS or post-processing
  DGPS
• reference stations established by The United
  States Coast Guard and other international
  agencies often transmit error correction
  information on the radio beacons that are already
  in place for radio direction finding (usually in
  the 300kHz range). Anyone in the area can receive
  these corrections and radically improve the
  accuracy of their GPS measurements. Many new GPS
  receivers are being designed to accept
  corrections, and some are even equipped with
  built-in radio receivers.
• if you don't need precise positioning immediately
  (real time). Your recorded data can be merged
  with corrections recorded at a reference receiver
  (through internet) for a later clean-up.
• http//www.fs.fed.us/database/gps/cbsalpha.htm

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http//www.geoplane.com/gpsneeds.html
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Project tasks can often be categorized by
required accuracies which will determine
equipment cost.
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Remote Sensing Basics

• Using electromagnetic spectrum to image the land,
  ocean, and atmosphere.

http//imagers.gsfc.nasa.gov/ems/waves3.html
When you listen to the radio, or cook dinner in a
microwave oven, you are using
electromagnetic waves. When you take a photo,
you are actually doing remote sensing
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Remote sensing platforms
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Passive Remote Sensing
Active Remote Sensing
E. transmission, reception, and pre-processing F.
processing, interpretation and analysis G.
analysis and application
A. the Sun energy source C. target D. sensor
receiving and/or energy source
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Major Passive Multi-Spectral Sensors

• LANDSAT MSS/TM/ETM (NASA, USA)
• SPOT-1, -2, -3
  (France)
• JERS-1 (optical sensor) (Japan)
• MODIS
  (NASA, USA)
• AVHRR (NOAA,
  USA)
• ASTER (NASA, USA, and
  Japan)
• IRS-1A, -1B, -1C, 1D (India)
• IKONOS (Space
  Imaging, USA)

Hyper-Spectral Sensor

• AVIRIS (NASA, USA)
• HyMap (Australia)

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Major Active Radar Sensor

• SIR-A, -B, -C (NASA,
  USA)
• RADARSAT (Canada)
• JERS-1 (radar sensor) (Japan)
• ERS-1
  (European)
• AIRSAR/TOPSAR (NASA, USA)
• NEXRAD (NOAA,
  USA)
• TRMM (NASA,
  USA)

Lidar Sensor

• ALTMS
  (TerraPoint, USA)
• FLI-MAP (John
  Chance, USA)
• ALTM (USA)
• TopoEye (USA)
• ATLAS (USA)

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NASA Landsat-7 (ETM) launched 4/15/1999
705 km
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Terra satellite launched on 12/18/1999
Spectrum Visible Near Infrared Thermal
Infrared Bands 36 Resolution (m) 250, 500, 1000
705 km
http//terra.nasa.gov/About/MODIS/modis_swath.html
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Global Geostationary Satellites
Earth radius 6,370 km Satellite altitude 35,800 km
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Image processing and modeling
The size of a cell we call image resolution,
depending on Such as 1 m, 30 m, 1 km, or 4 km
Image processing and modeling