Aerial Photography Exam

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Aerial Photography Exam
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2015-03-21 23:46:53
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Aerial Photography Exam
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  1. Passive Remote Sensing Systems
    Passive data acquisition systems, such as photography and multispectral scanning, record naturally occurring EM radiation that is reflected or emitted from the terrain.
  2. Active Remote Sensing Systems
    Active systems, such as microwave (radar), solar, laser sensors supply their own energy to illuminate the scene, and then record the amount of radiant flux scattered back toward the sensor system.
  3. Types of remote sensing
    • Imaging radar
    • Laser profiler
    • Radar altimeter
    • Aerial photography
    • Visible/near infrared scanner
    • Thermal infrared scanner
    • Passive microwave radiometer
  4. Wavelength spectrum
    Ranges from the smallest being the gamma ray at 10-12 to radio being at about the size of 103
  5. Which Landsat bands used for which different purpose? What are the wavelengths associated with each one?
    • Green (wavelength: .5-.6): sediment-laden water, delineates areas of shallow water
    • Red (wavelength: .6-.7): cultural features
    • Near infrared (wavelength: .7-.8): vegetation boundary between land, water & landforms
    • Near infrared (wavelength: .8-1.1): penetrates atmospheric haze best, emphasizes vegetation, boundary between land and water, and landforms
  6. True color image
    R, G, B
  7. Color infrared image
    IR, R, G
  8. 4 Properties of electromagnetic energy
    • Reflectance
    • Absorptance
    • Transmittance
    • Refraction
  9. Reflectance
    The ratio of the energy reflected from an object to the energy incident upon the object is reflectance.
  10. Absorptance
    When the rays do not bounce off the surface and do not pass through it they are converted to other forms of energy, such as heat
  11. Transmittance
    Propagation of energy through a medium
  12. Refraction
    • Bending of transmitted light rays at the interface of a different medium
    • Change in velocity as it passes from one medium to another.
    • Short wavelengths are bended more than longer ones.
  13. What are the factors that may impact the quality of images?
    • Haze
    • Tilt
    • Hotspot
    • Cover type
    • Cloud and shadow
    • Print contrast
  14. What are the four sensor resolutions?
    • Spatial lines/rows
    • Spatial columns
    • Spectral: bands
    • Radiometric: brightness value range (typically 8 bit)
  15. What’s the definition for vertical aerial photograph?
    Camera lens looking directly down up to 3° angle
  16. Low Oblique Aerial Photography can be characterized by:
    • Only covers a relatively small area.
    • The ground features have a familiar view
    • It does not show the horizon.
  17. High Oblique Aerial Photography can be characterized by:
    • It covers a very large area (not all usable).
    • Ground features vary from the very familiar to unfamiliar, depending on the height.
    • The horizon is always visible.
  18. Advantages of vertical as compared to oblique aerial photographs
    • Relatively constant scale across images
    • Easier and accurate measurements of size, distance, direction
    • Can be used within limitations as a map substitute by adding a grid system and marginal data
    • Sometimes easier to interpret than an oblique because of constant scale
    • Effective for stereoscopic study
  19. Advantages of oblique as compared to vertical aerial photographs
    • Covers larger area when taken from the same altitude with the same focal length lens
    • May be useful for areas frequently covered by cloud
    • Similar to the view from an observer located on a hill or a high tower, which makes manmade objects more recognizable
    • Shadow for depth
    • May show features that are not viewable from a vertical angle
    • E.g., caves or objects under the edge of a forest cover
  20. Principle Point (PP) (image slide 15 in 2-4)
    • The point that is perpendicularly projected through the center of the lens and intersects the photo image
    • It is the geometric center of the image and is assumed to coincide with the intersection of the x and y axes
  21. Conjugate Principal Point (CPP)
    Point in overlapping photo that is equivalent to principal point of adjacent photograph
  22. Nadir
    The point vertically beneath the camera lens at the time of exposure where a plumb line extended from the camera lens intersects the ground.
  23. Isocenter
    The point on the photo that falls on a line approximately halfway between the principle point and the nadir
  24. Distortion
    Any shift in the position of an image on a photograph that alters the perspective characteristics of the image
  25. Displacement
    Any shift in the position of an image on a photograph that does not alter the perspective characteristics of the photograph
  26. Types of distortion
    • Film & print shrinkage
    • Atmospheric refraction of light rays
    • Image motion
    • Lens distortion
  27. Types of displacement
    • Curvature of the Earth
    • Tilt
    • Topographic or relief, including object height
  28. Four types of stereoscopes
    • (1) the lens stereoscope
    • (2) the mirror stereoscope
    • (3) the scanning stereoscope
    • (4) the zoom stereoscope
  29. Scale measurements
    • Representative fraction (RF)
    • Photo scale reciprocal (PSR)
    • Equivalence
  30. Horizon
    • Measurements
    • Areas
    • Distance
  31. Vertical measurements
    • Measuring heights on single aerial photographs: the topographic displacement method and the shadow method
    • Measuring heights by parallax differences
  32. Three different formats of scale
    • Representative fraction (RF)
    • Photo scale reciprocal (PSR)
    • Equivalence (commonly used by maps)
  33. RF
    • Representative fraction
    • The ratio of a distance on the photo to the same distance on the ground can be expressed as a simple fraction (e.g., 1/24,000).
    • Unitless
  34. PSR
    • Photo scale reciprocal
    • The ratio of the ground distance divided by the photo distance; both distances are expressed in the same units.
    • The inverse of RF and is also unitless
  35. PSR formula
    • Photo scale reciprocal
    • GD (ground distance = difference between height of flight & ground level) / PD (photo distance = focal length)
  36. Vertical measurements
    • h / H = d /r So h = d (H) /r where:
    • d = photo displacement (same units as datum)
    • r = radial distance on the photo from nadir to the displaced point (in. or mm)
    • h = height of the object (vertical distance between 2 elevations)
    • H = A-E (flying height above datum)
    • A = altitude of aircraft above sea level
    • E = elevation of datum
  37. Parallax:
    • Apparent shift in the position of a body with respect to a reference point caused by a shift in the point of observation
    • Pa = Xa - Xa'
    • Pa = parallax at point A
    • Xa = measured x coordinate of image a on the left photograph of the stereo pair
    • Xa' = x coordinate of image a' on the right photograph
  38. Landform
    The geologist may describe landform in terms of surface characteristics that yield evidence as to geological structure of features of the Earth’s crust and may use such terms as faults, joints, domes, and basins
  39. Dendritic drainage patterns
    • The most common pattern characterized by a treelike, branching system where the branches (tributaries) join the stem (main stream) at acute angles.
    • This drainage system indicates homogeneous rock and soil materials with little or no structural control.
    • Soft sedimentary rocks, volcanic tuff, and dissected deposits of thick glacial till typify the dendritic pattern.
  40. Dendritic drainage patterns
  41. Trellis drainage patterns
  42. Trellis drainage patterns
    • modified dendritic forms where secondary steams occur at right angles to the main stream with the tertiary streams at right angles to the secondary streams
    • This type of pattern is typical of tributaries eroded in belts of tightly folded sedimentary rock.
  43. Annular Pattern
    Formed when stream courses adjust to follow a circular path around the base of resistant hills.
  44. Annular Pattern
  45. Braided Patterns
    • It occurs when stream velocity becomes insufficient to carry bed and suspended loads, depositing them in the channels.
    • The braided pattern develops on broad floodplains or alluvial terraces and is controlled by the load of the stream.
    • Braided stream channels are good sources of sand and gravel, and large volumes of water can often be obtained from shallow wells sited along their banks.
  46. Braided Patterns
    • Anastomotic Patterns
    • Characteristic of mature floodplain drainage
    • The meandering of the mainstream produces meander scrolls or loops and inter-locking channels along its serpentine course; drainage features include meander scars and oxbow lakes.
  47. Pinnate Patterns
  48. Pinnate Patterns
    • The drainage follows a featherlike branching pattern composed of many short, parallel gullies and tributaries that intersect mainstreams at slightly acute angels upstream; headwater basins are often pear-shaped.
    • The pinnate pattern, a modification of dendritic drainage, indicates a high silt content of the residual soil and typically forms where loess blankets an area.
  49. Sinkhole Patterns
    • The sinkhole, or swallow-hole, pattern consists of short streams that end in depressions or that disappear and flow underground; these subterranean streams may reemerge at the surface as large springs.
    • The bedrock underlying the areas in which this pattern develops is normally massive limestone, where pits and sinks have formed by chemical solution or by the collapse of caves (i.e., karst topography).
  50. Sinkhole Patterns
  51. Deranged Drainage Patterns
    • or disordered, pattern is non-integrated and is characterized by swamps, bogs, small ponds or lakes, or meandering streams.
    • This usually indicates a young landform with low topographic profile, high water table, and poor drainage.
  52. Deranged Drainage Patterns
  53. Sedimentary Rock Types
    include conglomerates (unconsolidated sand and gravel), sandstone, siltstone, limestone, and coal. Limestone and coal are examples of organic sources
  54. Glaciated Landscapes
    • Created by the carving action of glaciers and the deposition of this material at lower elevations
    • 10% of the Earth’s surface at present
  55. Eolian Landscape
    • About 30% of the U.S. is covered by eolian sediments.
    • Eolian landscapes consist of sand dunes and loess, or silt deposits.
    • The term loess (meaning "crumbly" in German) is used to describe silt textured eolian material. Loess can be interpreted as an accumulation of wind-blown dust, usually of glacial origin.
    • Sand dunes occur close to the source, and loess, being made up of much smaller particles, if often carried great distances by wind and covers large areas.
  56. A dune is a hill of sandformed by eolian processes
  57. Fluvial landscapes
    • Fluvial landscapes refer to those features formed by stream erosion, transportation, and deposition.
    • These deposits are frequently stratified by particle size because different water velocities allow differential settling of different sized material.
  58. Fluvial landscape view from LiDAR-derived DEM
  59. Mass Wasting
    • Defined as downslope movement of rock material (including soil) under the influence of gravity, but without a transporting agent such as wind, flowing water, or glacial ice
    • Also known as slope movement or mass movement
    • Even though flowing water is excluded from our definition, non-flowing water is a major contributing factor in mass wasting through its action as lubricant.
  60. Talus cones produced by mass wasting, north shore of Isfjord, Svalbard, Norway
  61. Sedimentary Rock Types
    include conglomerates (unconsolidated sand and gravel), sandstone, siltstone, limestone, and coal. Limestone and coal are examples of organic sources
  62. Glaciated Landscapes
    • Created by the carving action of glaciers and the deposition of this material at lower elevations
    • 10% of the Earth’s surface at present
  63. Fluvial landscapes
    • Fluvial landscapes refer to those features formed by stream erosion, transportation, and deposition.
    • These deposits are frequently stratified by particle size because different water velocities allow differential settling of different sized material.
  64. Mass Wasting
    • Defined as downslope movement of rock material (including soil) under the influence of gravity, but without a transporting agent such as wind, flowing water, or glacial iceAlso known as slope movement or mass movement
    • Even though flowing water is excluded from our definition, non-flowing water is a major contributing factor in mass wasting through its action as lubricant.
    • Defined as downslope movement of rock material (including soil) under the influence of gravity, but without a transporting agent such as wind, flowing water, or glacial ice
    • Also known as slope movement or mass movement
    • Even though flowing water is excluded from our definition, non-flowing water is a major contributing factor in mass wasting through its action as lubricant.
    • Mass wasting is usually a result of a combination of two factors:
    • The presence of structurally weak bedrock, which are deep-seated zones of weakness.
    • The moisture status of different strata.
    • Disturbance caused by human activity on the landscape or by natural earth movement can easily trigger mass movement of these potentially unstable areas.
  65. What is Image classification?
    • Classification process is designed to extract useful information from remotely sensed data
    • Image processed to put each pixel into a category
    • Classification process is designed to “teach” the computer how to extract the same information that the human extracts automatically and/or needs for specific management and research agendas.
    • Result is a vegetation map, land use map, or other map grouping related features.
    • Categories are defined by the intended use of the map
  66. Land cover
    Type of material present on the landscape (e.g., water, sand, crops, forest, wetland, human-made materials such as asphalt)
  67. Land use
    Type of use on/with the land surface (e.g., agriculture, commerce, settlement)
  68. Rules for land-cover and land-use classification schemes
    • Mutually exclusive
    • No fuzziness of any classes (e.g., deciduous forest and ever-green forest).
    • Exhaustive
    • All land-cover classes present in the landscape are accounted for and none have been omitted.
    • Hierarchical
    • Sub-level classes may be hierarchically combined into a higher-level category that makes sense.
  69. Methods used to select optimal bands for image classifications
    • Select the bands that are most effective in discriminating each class from all others
    • Graphic methods
    • Statistical methods
    • Use different spectral response of different materials to separate DN values (e.g. plot red vs. NIR)
    • Feature Space Image
  70. Supervised vs. Unsupervised Classification
    • Supervised requires the analyst to identify known areas
    • Unsupervised determines a set number of categories based on a computer algorithm
    • Hybrid classifiers are a mix of the two
  71. Hard vs. soft classification
    • Hard methods allow a pixel to be identified only with a single cluster, So many pixels will be incorrectly labeled
    • Soft /fuzzy logic allows partial membership
    • Instead of a water pixel, it could be 0.7 water and 0.3 forest
  72. Pixel vs. object based classification
    • The result is the creation of image objects defined as individual areas with shape and spectral homogeneity which one may recognize as segments or patches in the landscape.
    • Homogeneous image objects are then analyzed using traditional classification algorithms (e.g., nearest-neighbor, minimum distance, maximum likelihood) or knowledge-based approaches and fuzzy classification logic.
    • E-cognition, Definiens and Trimble
  73. Variation of input channels for classification
    • Not just bands how many and which ones?
    • Landsat TM bands
    • Channels created from Bands
    • Ratios
    • Indices
    • Greenness
    • DEMs
    • Use of masks
    • Context is derived from spatial relationships within the image
    • Can operate on either classified or unclassified scenes
    • Usually some classification has been done
    • It reassigns pixels as appropriate based on location (context)

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