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Copyright © John Lindsay, 2015


The Earth From Space

Flight Planning

John Lindsay
Fall 2015


Jensen Chapter 4, pg. 124-125

Image Acquistion

  • There exists an enormous archive of earth imagery both with respect to historical aerial photography and satellite imagery.
  • Usually held by federal/provincial/state repositories.
  • In Canada, the record extends 80 yrs back.
  • Hard-copy vs. scanned digital vs. digital
  • Varying cost of purchase.

SWOOP Images

  • Southwestern Ontario Orthophotography Project (SWOOP) 2010
  • 0.3 m pixel resolution orthophotos & 2-10 m DEM
  • Access through the Data Resource Centre
  • Free access for UofG

SWOOP image
DRAPE image

National Aerial Photo Library

  • Other Canadian AP’s through the National Aerial Photo Library of Canada, Ottawa
  • About $15 for a contact print and $30 for a pan scanned digital image (600 dpi)
  • A typical project area could be 30 photos in size = $900.

When is archive data unsuitable?

  • If existing data is out of date
  • Wrong season
  • The wrong scale for use
  • Poor quality
    • Might be due to degradation of film, poor weather/atmospheric conditions, unsuitable film type/spectral bands, etc.

When is archive data unsuitable?

  • In these situations, you must contract the acquisition of new imagery

  • This is always more expensive than purchasing archived data

New image acquisition—things to remember

  • Timing—usually a very small window
  • Scale (flying height and focal length)
  • Required percent overlap between photos
  • Flightline (number, orientation)
  • Film type
  • Camera type and characteristics
  • Aircraft capabilities

Time of Day Considerations

  • When the sun angle is less than 30° long shadows can obscure valuable information.

  • Can be very useful for interpreting terrain though.

  • When the sun angle is quite high hot spots can be present...

Hot Spots

  • Unusually bright spot on photo.
  • Pronounced over water and forest.
  • Occurs when sun angle is greater than about 52°.
hot spot image
(source: Paine and Kiser, 2001)

Weather Considerations

  • Excessive humidity can cause image degradation due to scattering.
  • Cloud cover also degrades images.
  • Best to acquire after a front goes through.
  • Rain washes the particulates out of the atmosphere
  • Strong winds cause problems too...

Drift and Crab

Drift and crab

Flightlines over a project area

Drift and crab
(source: Jan Mersey)

Flightlines over a project area

  • Must start by determining the mission constraints:
    • Photo scale
    • Camera focal length
    • Film format (e.g. Large format)
    • Image overlap

Photo Mosaic

  • Multiple overlapping air photos are 'stitched' together
  • Traditionally done by hand now usually done using software
Photo mosaic

Photo Mosaic

Notice that the are radiometric differences between the images apparent as unmatched tonal variation among photos
Photo mosaic
(source: unknown)

Types of Mosaics

  • Index mosaics
    • Usually prepared for the purpose of providing an index to individual photos in a series
  • Uncontrolled mosaics
    • Uses best fit but because of tilt of aircraft between exposures and topographic displacement, these mosaics are not reliable
  • Controlled mosaics
    • Use ground control points and rectified imagery
Photo mosaic
(source: Jensen 2007)