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Copyright © John Lindsay, 2015

GEOG*2420

The Earth From Space


Flight Planning



John Lindsay
Fall 2015

Readings

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 map
SWOOP image
DRAPE image

National Aerial Photo Library

  • Other Canadian AP’s through the National Aerial Photo Library of Canada, Ottawa
  • http://airphotos.nrcan.gc.ca/prod_e.php
  • 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  • If existing data is out of date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
(source: http://www.nrw.qld.gov.au/museum/articles_complete/mapping/aerial.html)

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)