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Aerial Photography

Aerial Photography.

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Aerial Photography

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  1. Aerial Photography Aerial platforms are primarily stable wing aircraft. Aircraft are often used to collect very detailed images and facilitate the collection of data over virtually any portion of the Earth's surface at any time. The scale and quality of the data collected is affected by several factors including, but not limited to, altitude of the aircraft, position of the plane, and the quality of the photographic equipment used.

  2. Camera

  3. Cameras Cameras view an area on the ground and after the light passes through the lens it is recorded onto the exposure plane.

  4. Cameras The area captured by the camera is affected by the: • Focal length of the lens • Platform altitude • Format and size of the film Focal length is the distance from the center of the lens to the exposure plane. The longer the focal length, the smaller the area on the ground that is recorded, but the result is a more detailed photograph.

  5. Cameras Cameras use light sensitive film which records UV, Visible and Near Infrared wavelengths.Three types of images are possible: • Black & White • True Color • Color IR or False Color

  6. Cameras Camera AnglesWhen the camera is pointed directly at the ground, a vertical photo is taken, thus reducing distortion. Vertical photos are used when high resolution is required. When the camera is pointed to the side of the aircraft, an oblique photo is taken. Oblique photos contain more distortion, however they are good for visualizing height differences.

  7. Satellite Imagery There are two types of sensors: • Passive • Active Passive sensors record EMR that originates from the sun and is reflected off of the objects it encounters.Active sensors provide their own energy source and record the reflected response as it interacts with various objects.

  8. Examples of Sensors Examples of Passive Sensors: • Landsat MSS & TM • SPOT • IKONOS Examples of Active Sensors: • Radar • Sonar

  9. Passive Sensors Multispectral Scanning • Many electronic (as opposed to photographic) remote sensors acquire data using scanning systems, which employ a sensor with a narrow field of view (i.e. IFOV) that sweeps over the terrain to build up and produce a two-dimensional image of the surface. • A scanning system used to collect data over a variety of different wavelength ranges is called a multispectral scanner (MSS) • There are two main modes or methods of scanning employed to acquire multispectral image data - across-track scanning, and along-track scanning.

  10. Multispectral Scanning Across-track scanning • rotating mirror (A). • A bank of internal detectors (B) • The IFOV (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).

  11. Multispectral Scanning Along-track scanning • Each line is scanned from one side of the sensor to the other, using a rotating mirror (A). • A bank of internal detectors (B), each sensitive to a specific range of wavelengths, detects and measures the energy for each spectral band • The IFOV (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). Pushbroom scanner

  12. Multi-Spectral Scanner • 4 filters produce spectral bands • 0.5 - 0.6 µm (green) • 0.6 - 0.7 µm (red) • 0.7 - 0.8 µm (photo-IR) • 1.1 µm (near-IR). • Light through each filter reaches its set of six electronic detectors (24 in all) that subdivide the cross-track scan into 6 parallel lines, each equivalent to a ground width of 79 m (259 ft).

  13. Passive Sensors Landsat MSS (Multispectral Scanner) - 1972Spatial Resolution: 56m x 79m Spectral Resolution: 4 Bands Temporal Resolution: 16 days Swath: 185 km

  14. Passive Sensors Landsat TM (Thematic Mapper) - 1982Spatial Resolution: 30m x 30m Spectral Resolution: 7 Bands Temporal Resolution: 16 days Swath: 185 km

  15. Passive Sensors SPOT Panchromatic - 1986Spatial Resolution: 10m x 10m Spectral Resolution: 1 Band Temporal Resolution: 26 days Swath: 60 km

  16. Passive Sensors SPOT XS (Multispectral) - 1986Spatial Resolution: 20m x 20m Spectral Resolution: 3 Bands Temporal Resolution: 26 days Swath: 60 km

  17. Passive Sensors IKONOS Panchromatic - 1999Spatial Resolution: 1m x 1m Spectral Resolution: 1 Band Temporal Resolution: 3 days Swath: 11 km

  18. Passive Sensors IKONOS Multispectral - 1999Spatial Resolution: 4m x 4m Spectral Resolution: 4 Bands Temporal Resolution: 3 days Swath: 11 km

  19. Active Sensors RadarRadar data are produced when a radar transmitter emits a beam of micro or millimeter waves, the waves reflect from the surfaces they strike, and the backscattered radiation is detected by the radar’s system’s receiving antenna, which is tuned to the frequency of the transmitted waves.Radar microwaves can penetrate the atmosphere day or night under virtually all weather conditions, providing data even in the presence of haze, light rain, snow, clouds, or smoke.

  20. Sensor System • real aperture radar • microwave • energy emitted across-track • return time measured (slant range) • amount of energy (scattering) • synthetic aperture radar • microwave • higher resolution - extended antenna simulated by forward motion of platform • ERS-1, -2 SAR (AMI), Radarsat SAR, JERS SAR

  21. MSS Scene of California • Urban is most reflective in Bands 4 and 5; • Suburban is strong in Bands 4 and 7 (the latter tied to the influence of planted vegetation). • The signatures for forest and healthy croplands are similar but the heights of the bars for Bands 6 and 7 are greater for the crops; • the bar heights for small grains and fallow fields are similar but the response for Bands 4 and 5 is just a bit higher than for 6 and 7

  22. Thematic Mapper • Band 1 is superior to MSS 4 in detecting some features in water • Band 5 is sensitive to variations in water content • Band 7 likewise reacts to moisture contents and is especially suited to detecting hydrous minerals (such as clays • Band 6 can distinguish a radiant temperature difference of ~ 0.6 degrees C

  23. Thematic Mapper Characteristics Band Wavelength Response Resolution 1 0.45 - 0.52 Blue-Green 30 2 0.52 - 0.60 Green 30 3 0.63 - 0.69 Red 30 4 0.76 - 0.90 Near IR 30 5 1.55 - 1.75 Mid-IR 30 6 10.40 - 12.50 Thermal IR 120 7 2.08 - 2.35 Mid-IR 30

  24. Other Satellite Systems • AVHRR • 5 channel, visible, near-infrared, thermal portions of spectrum • Used for studying vegetation conditions, regional tracking, snow cover, continent analysis, geophysical characteristics (temperature) • GOES • geosynchronous orbit for meteorological applications

  25. SPOT vs. Landsat

  26. SPOT Color and Panchromatic

  27. Merging Data Sets • Merge of a Landsat TM subscene rendered in IHS (Intensity; Hue; Saturation) color and a 2-meter (6.6 feet) resolution space photo onboard the Russian Mir Station

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