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CU-Boulder GEOG 5093 - Lecture Notes

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GEOG/GEOL 4093 Remote Sensing of the Environment Lecture 5 Outline of today’s lecture • EMR Interaction With Mater • Remote Sensing Platforms • Aircraft • Satellites • GPSEMR Interaction With Matter Radiative properties of a natural surface • Radiation incident upon a surface must either be transmitted (t) through it, reflected (a) from the surface or be absorbed (z). • For solar radiation, a is referred to as the surface albedo • If we consider only part of the EM spectrum, a is referred to as the spectral albedo • Albedo is the percent of incident solar energy that is reflected from a surface Transmissivity + Reflectivity + Absorptivity = 1Albedo (reflectivity) of various surfaceAttenuation The reduction of Intensity of EMR as it passes through a medium. Sometimes called extinction (Combination of absorption and scattering) EMR Interaction With MatterAtmospheric Scattering (Red / UV)4 = (0.6/0.3)4 = 16 Explanation why sky is blue Scattering intensity of Blue light = (0.45)-4 = 24.4 Scattering intensity of Green light = (0.50)-4 = 16.0 Scattering intensity of Red light = (0.65)-4 = 5.6Atmospheric Scattering At sunset, solar radiation must traverse a longer path through the atmosphere. Viewing a setting sun, the energy reaching the observer is largely depleted of blue radiation, leaving mostly red wavelengths (Rayleigh). Dust and smoke add additional scattering with a wavelength dependence that increases the red-sky effect (Mie) Red Sky at Nighthttp://addins.wrex.com/blogs/weather/?p=7171Atmospheric ScatteringAtmospheric Effects - Scattering Particle size between 0.1 to 10 times of λ Particle size << 0.1 times of λ Particle size > 10 times of λhttp://www.chrisandrewart.co.uk/artwork/night%20devine.htmhttp://www.newinfo2day.com/nature/why-is-the-sky-blue/Asymmetric OH Stretch Symmetric OH Stretch HOH Bend Atmospheric Absorption This absorption is the transfer of electromagnetic energy to the molecules with which the EMR comes in contact with.Atmospheric AbsorptionAtmospheric Windows • Regions in the EM spectrum where energy can be fully transmitted • 0.3-0.7 mm UV and visible light • 3-5 mm emitted thermal energy from Earth • 8-11 mm emitted thermal energy from Earth • 1 mm-1 m radar and microwave energyPlatforms for Remote Sensing • The main platforms for remote sensing are – Aircraft – Satellites • Other useful platforms are – Towers – Balloons – Kites1858 1900 1950 1990 1970 Balloon Aircraft Space Program Landsat-4 Space Shuttle Landsat-1 Sputnik Meteorological Satellites 2010 ERS-1 U n i t e d S s a t t e Commercial Satellites Pigeon camera Development of remote sensing systems Adaped from Chuvieco and Huete 2010 SPOT 5 RADARSATC – Camera S – Scanner R – Radar P – Passive microwave Recorder 1 m 10 m 100 m 1000 m 10 km 100 km 1000 km 36 000 km• Features – Very convenient – On-board repairs possible – Range of altitudes from meters to a kilometers – Speed: 0 – 300 m/s – Height determines scale, coverage, and resolution – Speed determines linear sampling rate Platforms: Aircraft• Navigation Electronic navigation system give the aircraft’s true position – Position • Loran: Ground based radio transmitter • GPS: Satellite based radio transmitter • Ground control points – Natural features of know location – GCPs should not have a tendency to change over time, examples for ideal GCPs are: road intersections and airport runways – Marker on the ground Marker on the groundPlatforms: SatellitesPlatforms: Satellites • Advantages – Increased platform speed – Continuity of missions – Better data coverage – Homogeneous data collection – No political boundary issues • Disadvantages – On-board repairs difficult or impossible – Sampling constrained by orbital geometryGlobal Positioning System (GPS) NAVSTAR GPS USA Galileo GPS EU GLONASS GPS RussiaGlobal Positioning System (GPS) What is GPS • Space-based global navigation satellite system comprised of 24 GPS satellites • Provides reliable navigation and timing services to worldwide users on a continuous basis • All-weather, day and night, anywhere on or near Earth How does it works • Receiver precisely times signals sent by GPS satellites • Time is converted to distance from satellites • Three satellites allow determination of unique position (in theory) • Errors in timing require at least four satellites be used, with position accuracy increasing with number of satellites • Position is determined within the terrestrial reference frameGPS Satellite Network • Orbit Altitude approximately 12,000 miles • Two complete orbits in less than a day • Travel approximately 7,000 miles per hour • Solar powered with backup batteries (for eclipse and other interruptions • Small rocket boosters correct orbit as needed • Other facts – First satellite launched in 1978 – Network of 24 achieved in 1994 – Satellites designed to last about 10 years with replacements constantly being built – Each one weights approximately 2,000 pounds and is about 17 feet across with solar panels extended – Uses only about 50 watts or lesshttp://www.n2yo.comCivilian Applications • Surveying: Surveyors use absolute locations to make maps and determine property boundaries • Map-making: Both civilian and military cartographers use GPS extensively. • Navigation: Navigators value digitally precise velocity and orientation measurements. • Cellular telephony: Clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/cellular position detection for mobile emergency calls and other applications.Civilian Applications • Tectonics: GPS enables direct fault motion measurement in earthquakes. • Disaster relief/emergency services: Depend upon GPS for location and timing capabilities • GPS tours: Location determines which content to display; for instance, information about an approaching point of interest is displayed. • Geotracking: Vehicle tracking systems, person tracking systems, and pet tracking systems use GPS to locate a vehicle, person or pet. GPS Aircraft Tracking • Geotagging: Applying location coordinates to digital objects such as photographs and other documents for purposes such as creating map overlays. Credit: © Science/AAASGPS Military


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