Air Photos

Air Photos
- Remote Sensing
  - definition
    - acquiring information about objects
    - without coming into contact
    - instead use reflected EMR ("sun's energy") or our own energy source
    - e.g. eye sight, camera/detector (images: photos, satellite, radar, LiDAR, etc)
  - energy source (signal source)
    - passive - 'existing light energy' (photos, satellite images)
    - active - transmit/ receive energy
      - RADAR
      - LiDAR
  - Platform: most common detector location
    - satellite
    - plane / helicopter
  - capture of EMR
    - broad-band - "range of light we see" (panchromatic & colour film)
    - multi-band - 2+ distinct bands (R-G-B, IR, UV, etc.) - satellite images
- EMR
  - = "energy" that travels in the form of a wave emitted by the sun (stars)
  - EMR has a broad spectrum
    - gamma rays (short)
    - X-rays
    - UV
    - visible spectrum
    - infrared (reflected & thermal)
    - microwaves
    - radio (long)
  - atmospheric window
    - portion of EMR that passes through atmosphere to the ground
      - UV
      - visible light
      - IR (reflected & thermal)
      - radio waves
  - interactions of EMR with matter
    - reflection
    - transmission
    - refraction
    - absorption
    - emission
  - spectral signature
    - bands that get reflected ("what we see")
    - "unique combination" become signatures
- Activities (uses)
  - photogrammetry
    - obtain reliable measures & make maps
    - measures are
      - distance
      - direction
      - area
      - object height (displacement)
      - elevation of the ground
  - photo interpretation
    - ID objects and determine their significance
    - examples
      - timber (vegetation) types
      - habitat suitability
      - land use
      - landforms & soils
  - orienteering
    - use map/ photos to navigate and find features
      - photogrammetry for directions & dist. to "get around"
      - photo interp. to ID features & confirm location
- Types of air photos
  - oblique
    - at an angle
    - low
    - high
    - greater area covered
    - "natural" - terrain/objects easy to recognize
  - vertical (<3 degrees)
    - "straight down"
    - "uniform scale" (... not really)
      - measures possible
      - map-like, use for navigation
    - features not "masked" by neighbouring objects (... but forest canopy)
    - can be used to make maps
- Lights! Camera! Action!
  - EMR (review)
    - atmospheric window = transmittance of EMR = what's available to us
    - interactions (we capture reflection)
  - Camera
    - large (f = 1 ft = 30cm), neg. = 9 in. = 23cm
      - focal length = f = 1 ft = 30.5cm
      - or f = 15.5cm
    - "colour"
    - photo number
      - roll number
        
        focal length
        
        'company' or gov't (e.g. BC)
        
        C = colour, D = digital
        
        year (may be missing on older photos)
        
        roll of film
      - individual photo #
      - e.g. 30BCC05012 - 109
        
        30 cm focal length (30.5cm)
        
        15 = 15.3cm
        
        BC gov't
        
        C = colour
        
        05 = 2005 (not for older photos)
        
        012 = the 12th film roll
        
        109 = the 109th photo on that roll
  - Action
    - flight line
      - 60% endlap (for stereo)
      - 20-30% sidelap (ensures no missed area)
    - problems
      - drift
      - crab
      - tilt (turbulance or banking)