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Airbone platform


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Airbone platform

  1. 1. GEOG3610 Remote Sensing and Image Interpretation Current remote sensing systems Airborne Platforms and Sensors Classified by technology Active remote sensing Passive remote sensing Classified by platforms Airborne systems Spaceborne systems Classified by sensors Photographic remote sensing Digital remote sensing GEOG3610 Remote Sensing and Image Interpretation 3 Copyright, 1998-2006 © Qiming Zhou Airborne Platforms and Sensors Types of platforms and sensors Platforms Development of aerial photography The airborne platforms Airborne Spaceborne The types of aerial photographs Active Digital Airborne radar Satellite radar Sensors Cameras, films and filters Photogrammetry Photographic Aerial space mission photography photography Acquisition of aerial photographs Passive Airborne Satellite Digital scanner imagery 2 4Photographic Remote Sensing 1
  2. 2. GEOG3610 Remote Sensing and Image Interpretation Development of aerial photography Old air-borne platforms The photographic camera is the oldest and the most frequently used remote sensing instrument. 1859: Tournachon obtained balloon photographs of a small village near Paris. Above: Stalwart pigeon photographers prepare to work. The tiny pigeon cameras were designed 1909: Wright and a Pathé news in 1903 and weighed about 70g. Right: Peering cameraperson took motion pictures of down a camera viewfinder from the open cockpit of a Curtiss Jenny, a flier practices the Centotelli, Italy. early techniques of aerial photography. (Courtesy Strain and Engle, 1992) 5 7 1860 picture of Boston Harbour Airphoto – Hong This 1860 picture of Boston Harbour is Kong thought to be the 1945 first aerial photograph taken in the US. The exposure was made from a balloon at an altitude of about 365m above the ground 6 8Photographic Remote Sensing 2
  3. 3. GEOG3610 Remote Sensing and Image Interpretation Airborne platforms Remote sensing aircraft Airborne platforms include: High altitude platforms: high-altitude balloons, U-2 reconnaissance aircraft, etc. Mid-altitude platforms: normal aircraft Low altitude platforms: light aircraft, remotely piloted aircraft (RPA) Perspective views Mission-based data acquisition Mid-altitude remote sensing aircraft. 9 11 High-altitude airborne platforms Low-altitude platforms Left: a remotely piloted aircraft (RPA) flying at a very slow speed and low altitude of 30 meters. Right: a light two-seater Left: high-altitude balloon that can reach the aircraft that is capable of top edge of the atmosphere; Above: U-2 flying at a slow speed military spy aircraft that flies near 30,000 and low altitude of 100 meters. meters. 10 12Photographic Remote Sensing 3
  4. 4. GEOG3610 Remote Sensing and Image Interpretation Types of aerial photographs Vertical airphoto Depending upon the orientation of the camera’s optical axis with respect to the earth’s surface, airphotos are classified Vertical airphoto of as: Maipo wetland of Vertical airphotos Hong Kong and adjacent Shenzhen Oblique airphotos urban built-up area High-oblique (1997) Low-oblique 13 15 Orientation of an aerial camera High-oblique airphoto Orientation of an Vertical Low oblique High oblique High-oblique aerial camera for airphoto (horizon Film plane vertical, low-oblique, Lens included) of Yuen and high-oblique Op tic Long and rural area al photography. Also ax is of Hong Kong, by shown is the shape Lands Department and relative size of Horizon line of HKSAR (1999). the ground area associated with each type of photograph. 14 16Photographic Remote Sensing 4
  5. 5. GEOG3610 Remote Sensing and Image Interpretation Low-oblique airphoto Camera Low-oblique lens airphoto (horizon not A classical Carl shown) of Zeiss camara Aberdeen, lens with 180mm Hong Kong focal length, (1999). note marks of diaphragm and focus range. 17 19 The framing camera Multispectral camera Camera body lens - focal plane and focal length shutter - control exposure speed diaphragm - control apertures Film exposure film exposure - the quantity of light that is allowed to reach the film F/number = f / d (progressed by √2, ~1.4) A nine-lens Lens speed: light-gathering power of a lens = multispectral the F/number of the full aperture. camera. 18 20Photographic Remote Sensing 5
  6. 6. GEOG3610 Remote Sensing and Image Interpretation • The framing camera (cont.) Ground θ distance H • Angular field of view (AFOV) θ’ ⎛ L ⎞ ⎛W ⎞ ⎛ L2 + W 2 ⎞ H’ θ L = 2 arctan ⎜ ⎜2f ⎟ ⎟ θW = 2 arctan ⎜ ⎜2f ⎟ ⎟ θ D = 2 arctan ⎜ ⎟ θ ⎞ ⎜ ⎟ ⎛ ⎝ ⎠ ⎝ ⎠ ⎝ 2f ⎠ DL = 2⎜ H tan L ⎟ ⎝ 2⎠ Classification of Lens Angles ⎛ θ ⎞ D’ D DW = 2⎜ H tan W ⎟ Range of Angles Name ⎝ 2 ⎠ < 60° Narrow angle • θ = 40° 60 - 75° Normal angle θ = 70° θ = 90° 75 - 100° Wide angle θ = 110° > 100° Super-wide angle 21 23 Lens angles in 3-dimensional Films and filters space Image format Black and white films panchromatic or infrared W Colour films natural colour and colour infrared θL L θD θW Lens D 22 24Photographic Remote Sensing 6
  7. 7. GEOG3610 Remote Sensing and Image Interpretation A mapping camera Black-and-white film Silver halide grains Gelatin Generalised diagram Emulsion of a black-and-white film Base Backing UV Blue Green Red Infrared 2 Spectral-sensitivity Panchromatic Log sensitivity Infrared curves for 1 panchromatic, extended-red 0 Panchromatic panchromatic, and (extended red) infrared films -1 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Wavelength (µm) 25 27 Aerial survey cameras Panchromatic aerial photograph Aerial survey cameras and A panchromatic other equipment aerial photograph mounted inside of Tweed region, an airplane. North NSW, Australia 26 28Photographic Remote Sensing 7
  8. 8. GEOG3610 Remote Sensing and Image Interpretation Colour formation with a colour-reversal film A black-and-white infrared photo A. Original scene reflectance Blue Green Red White Black B. Film after camera exposure Activated Activated Blue-sensitive layer Yellow filter Activated Activated Green-sensitive layer Activated Activated Red-sensitive layer White light B G R B G R B G R B G R B G R C. Film after processing Yellow dye layer Magenta dye layer Cyan dye layer B G R B G R D. Resulting colours Source: Ross Alford Blue Green Red White Black ( 29 31 Normal colour and colour infrared Normal colour aerial photograph films Haze filter Yellow filter Blue-sensitive layer Yellow filter Infrared-sensitive layer Green-sensitive layer Green-sensitive layer Red-sensitive layer Red-sensitive layer A high-resolution Base Base (20cm) normal colour Backing Backing aerial photograph of a residential area in Normal colour film. A haze filter is Colour infrared film. A yellow filter Berlin. placed over the camera lens to must be used to stop ultraviolet (Courtesy GeoContent GmbH: stop ultraviolet radiation from and blue radiation from reaching reaching the blue-sensitive layer. the three emulsion layers. 30 32Photographic Remote Sensing 8
  9. 9. GEOG3610 Remote Sensing and Image Interpretation False-colour formation with a colour infrared-reversal film A. Original scene reflectance Using aerial photographs Blue Green Red Infrared Yellow filter Marginal information of an aerial B. Film after camera exposure Activated Infrared-sensitive layer photograph: Activated Green-sensitive layer obvious: name of the place, date of Activated Red-sensitive layer photograph, flight height, photo index, White light B G R B G R B G R B G R and producer C. Film after processing not-so-obvious: focal length of the Cyan dye layer Yellow dye layer camera lens, time of the photograph, Magenta dye layer position of the principal point of the photo B G R D. Resulting colours Black Blue Green Red 33 35 Colour infrared aerial photograph Marginal information Focal length of the camera lens Clock to show time of the photograph A high-resolution (20cm) colour infrared aerial photograph of a Notch to find residential area in principle point Berlin. (Courtesy GeoContent GmbH: Name of the place date of photograph, flight height, photo 34 index, and producer 36Photographic Remote Sensing 9
  10. 10. GEOG3610 Remote Sensing and Image Interpretation 3-D visualisation 3D 2D Visualization 3-dimensional photography Courtesy Dr Zhang Yun Department of Geodesy and Geomatics Engineering, University of New Brunswick, Canada Example of paired photographs that produce a 3-dimensional image when viewed through a stereoscope. 37 39 Flight 1 2 3 4 3-dimensional photography (cont.) mission for 3-dimensional photograph that was produced from a photograph pair that is stereo coloured as cyan for the left photo and red for the coverage right photo. The 3- dimensional vision can be 60% viewed using a coloured Aerial camera stations Forward overlap spectacles with cyan on are spaced to provide the left and red on the for about a 60% right. forward overlap of aerial photographs 20 to 30 % sidelap along each flight line 3D Visualization and a 20-30% sidelap for adjacent lines. 38 40Photographic Remote Sensing 10
  11. 11. GEOG3610 Remote Sensing and Image Interpretation Stereoscopes Geometry of a vertical airphoto Principal point D E Film plane f f DE = Lens C H AB ∠ACB = ∠DCE Desktop (left) Optical axis and pocket (top) H stereoscopes for stereo view of aerial photographs. A Nadir B 41 43 Photogrammetry Understanding distortion Photogrammetry: the technique of Perspective view obtaining reliable measurements of Systematic distortion controlled by the objects from their photographic images. field of view that is determined by f RF = Determination of scale (RF: focal length of the camera lens H representative fraction) size of the film media (e.g. 9 x 9 inches) PD RF = from focal length and altitude Random distortion specified as crab (MD )(MS ) from photo-map distance and tilt of aerial photographs PD from photo-ground distance RF = GD 42 44Photographic Remote Sensing 11
  12. 12. GEOG3610 Remote Sensing and Image Interpretation Factors to be considered Computing heights using A object sidelap Tilt f FOV Flight 30% displacement line crab Wan Chai urban area of Hong overlap Kong. The Building marked A shows great displacement 60% H because it is far away from the nadir. nadir 45 47 Computing heights Computing heights using stereoscopic parallax (cont.) d Using object displacement h= H r d = object length from base to top Stereo photo pair of Wan r = radial distance from nadir to top Chai urban H = flying height area of Hong P dP h= H Kong. Note P + dP Using stereoscopic parallax that the photo P + dP P = absolute stereoscopic parallax at the base pair must be correctly dP = differential parallax aligned for h = s tan α Using shadow length stereo view before α = sun’s elevation angle computing s = shadow length heights using parallax. 46 48Photographic Remote Sensing 12
  13. 13. GEOG3610 Remote Sensing and Image Interpretation Computing heights using shadow Seasonal consideration length Height = shadow × tan α Height α Shadow Summer (leaf on) and winter (leaf off) airphotos for the same ground area in western Pennsylvania 49 51 Acquisition of aerial photographs Hotspot Hotspot problem often Flight altitudes and focal lengths occurs with high sun Seasonal consideration angle for vertical photos, so that summer Time-of-day considerations mid-day flight mission Availability of existing photography should be avoided. In Hong Kong, the territory has been covered So at least once a year since late 1980’s. la rr ad Since 1993, the coverage has been made in Lens ia tio natural colour photographs. n The airphotos can be purchased from the land department. Nadir Hotspot 50 52Photographic Remote Sensing 13
  14. 14. GEOG3610 Remote Sensing and Image Interpretation Effects of 8 different illumination angles 53Photographic Remote Sensing 14