SPOT Panchromatic:
Images of the original SPOT Panchromatic of December, 1990, February, 1997, change detection using Red (Feb97) and Green (Dec90), change detection subtraction and division methods are displayed in Figure 3.
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Sydney metropolitan area covering ~38*38 kms
A=SPOT Panchromatic Dec 1990
B=SPOT Panchromatic Feb 1997
C=PanFeb97(Red) & PanDec90(Green)
D=Change Detection Subtraction method (Pan297-Panl290)
E=Change Detection Division method (Pan297/Pan1290)
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Figure 3. SPOT Panchromatic (Dec 90 & Feb 97) of Sydney Metropolitan area and change detections
Simple Red-Green combination change detection:
This is a very simple method to quickly check the changed areas by just using the Red gun for PanFeb97 and the Green gun for PanDec90. Where there are differences between the 2 dates imagery Red and Green colors are displayed and the areas where there are no differences Yellow color is displayed (Fig 3C). However, the method is only for visualization and changed areas cannot be mapped.
Change Detection - Subtraction method:
This method simply subtracts one date SPOT Pan from another (Feb97 Pan - Dec90 Pan). Using the Pseudocolor look-up-table the changed areas for the 2 dates SPOT Pan and the common areas can be mapped in three colors and changed areas can be mapped and can be converted to vector format. The changed areas of the 2 dates SPOT Pan are mapped as blue and red whereas the common areas are mapped and displayed in cyan color (Fig. 3D). The thresholds of the changed areas are defined by the step transformation where the changed areas are represented by the two extreme ends of the (Feb97 Pan - Dec90 Pan) histogram. The changed maps can then be verified with groundtruthing.
Change Detection - Division method:
This method simply divides one date SPOT Pan from another (Feb97 Pan / Dec90 Pan). Similarly, using the Pseudocolor look-up-table the changed areas for the 2 dates SPOT Pan and the common areas can be mapped in three colors. The changed areas of the 2 dates SPOT Pan are mapped as blue and red whereas the common areas are mapped and displayed in cyan color (Fig. 3E). The thresholds of the changed areas, mainly in the two ends of the (Feb97 Pan / Dec90 Pan) histogram, are also defined by the step transformation.
