change dec ti on
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This lecture reviews basic considerations whenThis lecture reviews basic considerations when
change information is extracted from digitalchange information is extracted from digital
remotely sensed data and some of theremotely sensed data and some of the
procedures to the study of change detection. procedures to the study of change detection.
Digital Change DetectionDigital Change Detection Why do we study change detection?Why do we study change detection?
It is believed that landIt is believed that land--use/landuse/land--cover change is a major cover change is a major
component of global change with an impact perhapscomponent of global change with an impact perhaps
greater than that of climate change.greater than that of climate change.
It is important that such changes be inventoriedIt is important that such changes be inventoried
accurately so that the physical and human processes ataccurately so that the physical and human processes atwork can be more fully understood.work can be more fully understood.
1. Classification scheme2. Geographic study area
3. Time period
4. Per pixel or object oriented approach
5. Temporal and spatial resolution
6. Phenological cycles
1. Classification scheme
2. Geographic study area
3. Time period
4. Per pixel or object oriented approach
5. Temporal and spatial resolution
6. Phenological cycles
Considerations for
change detection
Considerations for Considerations for
change detectionchange detection
Classifying Features
• Classification systems can be broad such as water/land, or detailed such as single family/multifamily dwelling. Thescale of the image will often dictate how finely you canclassify features.
• The USGS has developed a standard land use/land cover
classification system based in the works of Anderson 1976.
• Other classification systems have been develop by:
– GLUT (Georgia landuse trends)
– NARSAL ( Natural Resources Spatial Analysis Laboratory(NARSAL)
– CCAP (Coastal Change Analysis programs
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In agricultural crops, the
analyst must be aware
of when the crops were
planted.
A month lag in planting
date between fields of
the same crop can causeserious change
detection error.
In agricultural crops, theIn agricultural crops, the
analyst must be awareanalyst must be aware
of when the crops wereof when the crops were
planted. planted.
A month lag in plantingA month lag in planting
date between fields of date between fields of
the same crop can causethe same crop can causeserious changeserious change
detection error.detection error.
Environmental Parameter: Vegetation PhenologyEnvironmental Parameter:Environmental Parameter: Vegetation PhenologyVegetation Phenology
In coastal landscapes the analyst should be aware of
tidal differences
In coastal landscapes the analyst should be aware of In coastal landscapes the analyst should be aware of
tidal differencestidal differences
Environmental Parameter: coastal tidesEnvironmental Parameter: coastal tidesEnvironmental Parameter: coastal tides
•Image algebra
•Post classification comparison
•Binary mask
•An Ancillary Data Source As Date 1
•Visual on screen digitization
••Image algebraImage algebra
••Post classification comparisonPost classification comparison••Binary mask Binary mask
••An Ancillary Data Source As Date 1An Ancillary Data Source As Date 1
••Visual on screen digitizationVisual on screen digitization
Options for change detectionOptions for change detectionOptions for change detection
Image differencing involves subtracting the imagery of
one date from that of another.
It is possible to identify the amount of change between
two rectified images by band ratioing or image
differencing .
Image differencing involves subtracting the imagery of Image differencing involves subtracting the imagery of
one date from that of another.one date from that of another.
It is possible to identify the amount of change betweenIt is possible to identify the amount of change between
two rectified images bytwo rectified images by band ratioing band ratioing or or imageimage
differencing differencing ..
Image Algebra Change DetectionImage Algebra Change DetectionImage Algebra Change Detection
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PostPost--classification Comparison Change Detectionclassification Comparison Change Detection PostPost--classificationclassification
ComparisonComparison
Change DetectionChange Detection
Post-classification
Comparison
Change Detection
PostPost--classificationclassification
ComparisonComparison
Change DetectionChange Detection
Post-Classification Comparison
Change Detection: Change Matrix
PostPost--Classification ComparisonClassification Comparison
Change Detection: Change MatrixChange Detection: Change Matrix
Water Forest Urban
Water
Forest
Urban
1 2 3
4 5 6
7 8 9
From:
2000
To:
2007
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Steps
1. A traditional classification of Date 1 is performed
2. one of the bands (e.g., band 3) from both dates of imagery is
analyzed using image differencing to identify areas of
“change” and “no change” in the new image.
3. The change image is then recoded into a binary mask file
consisting of areas that have changed between the two dates.
4. The change mask is then overlaid onto Date 2 of the analysisand only those pixels that were detected as having changed
are classified in the Date 2 imagery.
StepsSteps
1.1. A traditional classification of Date 1 is performedA traditional classification of Date 1 is performed
2.2. one of the bands (e.g., band 3) from both dates of imagery isone of the bands (e.g., band 3) from both dates of imagery is
analyzed using image differencing to identify areas of analyzed using image differencing to identify areas of
““changechange”” andand ““no changeno change”” in the new image.in the new image.
3.3. The change image is then recoded into a binary mask fileThe change image is then recoded into a binary mask file
consisting of areas that have changed between the two dates.consisting of areas that have changed between the two dates.
4.4. The change mask is then overlaid onto Date 2 of the analysisThe change mask is then overlaid onto Date 2 of the analysisand only those pixels that were detected as having changedand only those pixels that were detected as having changed
are classified in the Date 2 imagery.are classified in the Date 2 imagery.
Binary Change Mask Applied to Date 2Binary Change Mask Applied to Date 2Binary Change Mask Applied to Date 2Change Detection Using A Binary Change Mask Applied to Date 2Change Detection Using A Binary Change Mask Applied to Date 2
Instead of using a remotely sensed image as Date 1 it is
possible to use a digital land cover map of the region.
For example, the U.S. Fish and Wildlife Service conducted a
National Wetland Inventory (NWI) of the United States at
1:24,000 scale.
Date 2 of the analysis is classified and then compared on a
pixel-by-pixel basis with the Date 1 information using post-
classification comparison methods.
Using An Ancillary Data Source As Date 1Using An Ancillary Data Source As Date 1 Change Detection Using An Ancillary Data Source As Date 1Change Detection Using An Ancillary Data Source As Date 1
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Visual OnVisual On--screen Change Detection and Digitizationscreen Change Detection and Digitization
In this process both digitized photographs (or images)
are displayed at the same time, side by side.
Both dates of aerial photography (or other type of
remote sensor data) are visually interpreted and
compared to detect change.
Changes are digitized on screen
In this process both digitized photographs (or images)In this process both digitized photographs (or images)
are displayed at the same time, side by side.are displayed at the same time, side by side.
Both dates of aerial photography (or other type of Both dates of aerial photography (or other type of
remote sensor data) are visually interpreted andremote sensor data) are visually interpreted and
compared to detect change.compared to detect change.
Changes are digitized on screenChanges are digitized on screen
A white arrow indicates
the direction of houses
removed from their
foundations.
Areas of beach erosion
are depicted as black
lines.
Areas of beach accretion
caused by HurricaneHugo are shown as
dashed black lines.
A white arrow indicatesA white arrow indicates
the direction of housesthe direction of houses
removed from their removed from their
foundations.foundations.
Areas of beach erosionAreas of beach erosion
are depicted as black are depicted as black
lines.lines.
Areas of beach accretionAreas of beach accretion
caused by Hurricanecaused by HurricaneHugo are shown asHugo are shown as
dashed black lines.dashed black lines.
Date 1
Date 2
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Land-use Maps