Remote Sensing Theory & Background

1. Remote Sensing Theory & Background GEOG370 Instructor: Christine Erlien

2. 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

3. 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

4. Silk Road, China Waterless plains of southern Algeria Grand Canyon http://www.remotesensingart.com/

5. Types of Remote Sensing • Type  Based on source of the energy recorded by the sensor • 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 • Active Remote Sensing: Energy collected by sensors is actively generated by a man-made device. • Examples: Radar, LIDAR (Light Detection and Ranging)

6. Active and Passive Remote Sensing AVHRR Thermal Image http://www.coml.org/edu/tech/count/srs1.htm QuikSCAT radar image http://nsidc.org/seaice/study/active_remote_sensing.html

7. Particle=photon Wavelength  Solar Radiation Electromagnetic radiation energy: Wave-particle duality. 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10-34 Js) Note: The shorter the radiations’ wavelength, the higher its frequency  the more energy a photon carries

8. Atmospheric windows Solar Electromagnetic Radiation

9. First Remote Sensing Image Tree Rooftop 1st permanent photograph (remotely sensed image), by Niepce in 1826. http://www.artlex.com/ArtLex/p/images/photo_niepce.lg.jpg

10. 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 http://rst.gsfc.nasa.gov/Front/overview.html

11. Military Intelligence 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 1940. British launched an air attack on the invasion forces  Germany forced to postpone & eventually abandon invasion

12. 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 1998-99 Cuba, 1962

13. Military Intelligence & Image Resolution 1 meter 2.5 meter 5 meter 10 meter 10 cm 25 cm 50 cm 100 cm http://rst.gsfc.nasa.gov/Intro/Part2_26e.html http://www.fas.org/irp/imint/resolve3.htm

14. 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: Ability to discriminate very slight differences in energy • Scanner types • Along-track • Across-track

15. 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). http://ccrs.nrcan.gc.ca/resource/tutor/fundam/chapter2/08_e.php

16. 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” http://ccrs.nrcan.gc.ca/resource/tutor/fundam/chapter2/08_e.php

17. Civil Remote Sensing Earth Resources Technology Satellite (ERTS-1; renamed Landsat 1) 1st satellite launched for peaceful purposes (1972) Satellite Launched Decom RBV MSS TM Orbit Landsat-1 23 Jul 1972 6 Jan 1978 1-3 4-7 none 18d/900km Landsat-2 22 Jan 1975 25 Feb 1982 1-3 4-7 none 18d/900km Landsat-3 5 Mar 1978 31 Mar 1983 A-D 4-8 none 18d/900km Landsat-4 16 Jul 1982 -- none 1-4 1-7 16d/705km Landsat-5 2 Mar 1984 -- none 1-4 1-7 16d/705km Landsat-6 5 Oct 1993 Launch Failure none none ETM 16d/705km Landsat-7 15 Apr 1999 -- none none ETM+ 16d/705km RBV: Return Beam Vidicon MSS: Multispectral Scanner TM: Thematic Mapper Decom: decommissioned

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

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

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

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

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

23. 255 Digital numbers (DN) 0 Radiance intensity Maximum Radiance Minimum Radiance RadiometricResolution 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

24. Landsat Images Alaska’s Aleutian Islands Mississippi River Delta http://earthasart.gsfc.nasa.gov

25. 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

26. SPOT Imagery http://www.spotimage.fr/automne_modules_files/gal/edited/r444_santiago3D_800x600.jpg

27. Ikonos Owner: Space Imaging Temporal resolution: 11 days Radiometric resolution: 11-bit Spectral bands spatial resolution Blue (0.45-0.52 4m Green (0.51-0.60) 4m Red (0.63-0.70) 4m NIR (0.76-0.85) 4m Panchromatic (0.45-0.90) 1m Swath width: 11km Orbit: Sun-synchronous; equatorial crossing time of 10:30am

28. IKONOS