Remote Sensing Theory & Background GEOG370 Instructor: Christine Erlien

Overview What is remote sensing Brief remote sensing history Photography enables remote sensing Film, then digital; balloons  satellites Satellite remote sensing Resolutions Scanner types Platforms

What is Remote Sensing? Remote  far away Sensing things from a distance Remote sensing is the science and art of obtaining information about a target through the analysis of data acquired by a device that is not in contact with the target under investigation. What we see & why Eyes: Sunlight is reflected onto our nerve cells in the retina. What we see: Visible spectrum (blue, green, red wavelengths) Remote sensing equipment allows us to sense electromagnetic radiation beyond the visible spectrum

/ Silk Road, China Grand Canyon Waterless plains of southern Algeria

Type  Based on source of the energy recorded by the sensor 1.Passive Remote Sensing: Energy collected by sensors is either reflected or emitted solar radiation. Reflected – must be collected during daylight hours Emitted – day or night as long as emissions large enough to record 2.Active Remote Sensing: Energy collected by sensors is actively generated by a man-made device. Examples: Radar, LIDAR (Light Detection and Ranging) Types of Remote Sensing

AVHRR Thermal Image QuikSCAT radar image Active and Passive Remote Sensing

Solar Radiation Electromagnetic radiation energy: Wave-particle duality. Particle=photon Wavelength Light speed: c=f c = speed of light (186,000 miles/second) f = light frequency: number of waves passing a reference per unit time (e.g., second). The amount of energy carried by a photon:  = hf h=Planck’s constant (6.626  Js) Note: The shorter the radiations’ wavelength, the higher its frequency  the more energy a photon carries

Solar Electromagnetic Radiation Atmospheric windows

First Remote Sensing Image 1 st permanent photograph (remotely sensed image), by Niepce in Tree Rooftop

Remote Sensing of Large Areas Early remote sensing  limited by means available to put the sensor (i.e., camera) high above the target The means: 1. Balloons 2. Pigeons 3. Gliders 4. Aircraft 5. Satellite

Remote sensing  a critical source of military intelligence for WWI & WWII, Cold War Remains a critical source of intelligence today Examples: WWI: British reconnaissance aerial photography revealed a major change in direction of the German forces advancing on Paris  allowed the Allied army to fortify its position and hold off the German advance to Paris WWII: German barges identified in canals near the coast of France in summer of British launched an air attack on the invasion forces  Germany forced to postpone & eventually abandon invasion Military Intelligence

Cold War: U-2 Aircraft Balloons can be easily shot down  high altitude aircraft called the U-2 built to collect remotely sensed data U-2 flies at 70,000 ft, putting it beyond the range of surface- to-air missiles & other aircraft (at that time) Remains a valuable means of collecting remote sensing data today President Bush used it during Gulf War in 1991 President Clinton used it in the war in Bosnia in Cuba, 1962

Military Intelligence & Image Resolution 1 meter5 meter2.5 meter 10 cm 10 meter 50 cm25 cm100 cm

Satellite Remote Sensing Resolutions Spatial: Area visible to the sensor Spectral: Ability of a sensor to define fine wavelength intervals Temporal: Amount of time before site revisited Radiometric: A bility to discriminate very slight differences in energy Scanner types Along-track Across-track

Across-track scanning Scan the Earth in a series of lines Lines perpendicular to sensor motion Each line is scanned from one side of the sensor to the other, using a rotating mirror (A). Internal detectors (B) detect & measure energy for each spectral band, convert to digital data IFOV or Instantaneous Field of View (C) of the sensor and the altitude of the platform determine the ground resolution cell viewed (D), and thus the spatial resolution. The angular field of view (E) is the sweep of the mirror, measured in degrees, used to record a scan line, and determines the width of the imaged swath (F).

Along-track scanning Uses forward motion to record successive scan lines perpendicular to the flight direction Linear array of detectors (A) used; located at the focal plane of the image (B) formed by lens systems (C) Separate array for each spectral band Each individual detector measures the energy for a single ground resolution cell (D) May be several thousand detectors Each is a CCD Energy detected and converted to digital data “Pushed" along in the flight track direction (i.e. along track). “Pushbroom scanners”

Civil Remote Sensing Satellite Launched Decom RBV MSS TM Orbit Landsat-1 23 Jul Jan none 18d/900km Landsat-2 22 Jan Feb none 18d/900km Landsat-3 5 Mar Mar 1983 A-D 4-8 none 18d/900km Landsat-4 16 Jul none d/705km Landsat-5 2 Mar none d/705km Landsat-6 5 Oct 1993 Launch Failure none none ETM 16d/705km Landsat-7 15 Apr none none ETM+ 16d/705km RBV: Return Beam Vidicon MSS: Multispectral Scanner TM: Thematic Mapper Decom: decommissioned Earth Resources Technology Satellite (ERTS-1; renamed Landsat 1) 1 st satellite launched for peaceful purposes (1972)

Data transmission to the ground, allows fast & efficient data delivery Landsat

Sun-synchronous orbit: Satellite always crosses the equator at precisely the same local time Landsat Orbit

Temporal Resolution: The shortest time needed to repeat the ground track Landsat Temporal Resolution

185 km Field of View 175km scene Landsat Satellite ground track 705km Spatial Resolution Pixel size= (30x30m) Landsat Swath Width & Field of View

Spectral resolution: The number of bands and the width of spectrum that each sensor covers Landsat 7 ETM+ Spectral Bands

Radiometric Resolution The number of levels of DN values is determined by the radiometric resolution of the instrument. For example, 8-bit system can differentiate 256 (0-255) levels of radiance Minimum Radiance Maximum Radiance Digital numbers (DN) Radiance intensity 0 255

Alaska’s Aleutian IslandsMississippi River Delta Landsat Images

SPOT (Systeme Pour l’Observation de la Terre) Along track scanning system (Pushbroom System) Sensors are pointable Allows repeat coverage from different angles Increases potential frequency of coverage of areas where cloud cover is a problem Ability to collect stereoscopic imagery Temporal resolution=26 days Radiometric resolution=8-bit

SPOT Imagery

Ikonos Owner: Space Imaging Temporal resolution: 11 days Radiometric resolution: 11-bit Spectral bands spatial resolution Blue ( m Green ( ) 4m Red ( ) 4m NIR ( ) 4m Panchromatic ( ) 1m Swath width: 11km Orbit: Sun-synchronous; equatorial crossing time of 10:30am

IKONOS