Change detection Flashcards
What do we need to know to detect land use change?
Where change has occured?
When did the change occur?
What are some examples of phenomena that can lead to land surface change?
Urbanisation
Deforestation
Changing agricultural land use patterns
Desertification
Natural disaster
Geomorphic process
Plant community
How does change detection work?
Identify pixels where change has occured, so you can calculate the extent to which change has occured
Why is it important to use images from the same time of year?
You can minimise the influence of:
Seasonal sun-angle
Plant phenological differences
Differences in planting agricultural crops
What are the 3 stages of change detection?
Image differencing
Temporal trajectory analysis
Post-classification comparison
How do you complete the ‘image differencing’ step?
Subtracting one imagery value from another
-pixel values of one image minus pixel values of the other image
Creates a difference image
Either positive, negative or 0 value
How do you determine whether land cover change is true or due to external factors?
Plot histogram- distribution curve
Anything in the central point is minor- likely due to external factors
The extremes- positive or negative are true land cover change
What does an image time series analysis include?
Multiple images- not just two images
What can a time series analysis tell you?
More information on the type of change that is occurring
Inflection point- specific date of change
Decrease in spectral index- removal of vegetation
How does post-classification analysis work?
Use land cover classes
Identify which pixels have changed from one land use type to another and to what extent
Why is post-classification analysis important?
To understand the nature of the change and the pressures on that environment
What are the 2 advantages of image differencing?
Simple method
Results are easy to interpret
What are the 2 disadvantages of image differencing?
Inadequate qualitative information regarding the nature of the change
Selection of change threshold values can be problematic
What are the 3 advantages of post classification?
Complete descriptive matrix changes between dates
Compensates for atmospheric changes between dates
Can control unwanted changes through class assignation
What are the 3 disadvantages of post classification?
Compounds classification errors in the original classification
Labour intensive
Time consuming
