Coherent Change Detection Esfahan, Iran

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Coherent Change Detection Esfahan, Iran

• Alex Rodrigues
• GMOSS WP20300 meeting at Royal Military Academy,
  Brussels
• 14 November 2005

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Data

• RADARSAT fine beam coherent triplet
• 20 September 2002
• 05 July 2003
• 29 July 2003
• Quickbird optical data
• 15 June 2004

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Co-registration

• Coherent SAR
• frozen speckle pattern
• coregistered SAR images using localised cross
  correlation of speckle patterns.
• compute cross-correlation over 49 small patches.
• Reject incoherent patches.
• Take mean shift of remaining patches and apply to
  entire image
• Coregistration accurate to 0.15 pixels
• Coregistration of 3 images was done as follows
• Earliest is master
• Middle image is coregistered to image 1
• Latest image is coregistered to image 1

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Coregistered SAR data Esfahan site
RADARSAT Colour Composite
Quickbird panchromatic
20 September 2002 5 July 2003 29 July 2003
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Coherence

• Compute coherence between pairs of images
• Similarity between pairs of images
• Several possibilities
• Earliest and middle - long time gap (10 months)
• Earliest and latest (not done here)
• Middle and latest - short time gap ( 1 month)
• Produce visual products
• Colour composites of SAR images and coherence
• Earliest, middle, coherence
• Middle, latest, coherence
• Visually inspect products

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Colour composites of SAR images and coherence

• Earlier SAR image 1 red
• Later SAR image 2 green
• Coherence between image 1 and image 2 - blue
• The colour scheme is as follows
• Yellow change to existing objects (eg building
  modification, object rearrangement)
• White and blue no change
• Red demolition, road building
• Green - construction

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20/09/2002, 05/07/2003, coherence
Middle
Earliest
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05/07/2003,29/07/2003, coherence
Middle
Latest
Much shorter time interval natural areas have
high coherence
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Conclusions

• Changes have been detected
• hard to spot requires a trained eye (and some
  guesswork!)
• RADARSAT resolution is not high enough
• Reliable change detection requires continuous
  monitoring with regular repeats (so that changes
  between images of fixed temporal difference are
  compared)
• Coherent image acquisition places stringent
  requirements on satellite orbit control
• Would like to try to create some rules and try to
  classify the SAR/coherence composites
• Fusion with optical data

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