SPOT Multi_Spectral:
The same process was carried out on the SPOT Multi-Spectral images of the Feb97 and Dec90 Sydney Metropolitan area (Figure 4). However, instead of comparing one band at a time, between XS1 or XS2 or XS3 of Feb97 and Dec90, PC1 of the XS123 of the Feb97 and Dec90 are used. Since Principle Component Analysis maps co-variances of the three input bands, XS1,2,3 into a new axis PC1 (Richards, 1995), it represents the common information of the three input bands. If the user wants to analyze changes in particular Visible Green, Red and Infrared, he/she can do so very easily using the LCAW.
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Sydney metropolitan area covering ~38*38 kms
A=SPOT XS321 RGB Dec 1990
B=SPOT XS321 RGB Feb 1997
C=PCI XS Feb97(Red) & Dec90(Green)
D=Change Detection Sub traction method (PCI XS297-XS1290)
E=Change Detection Divsion method (PC1XS297/Xs1290)
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Figure 4. SPOT Multi-Spectral (Dec 90 & Feb 97) of Sydney Metropolitan area and change detections
Discussion
All the simple Red, Blue color display, Subtraction and Division change detection techniques, using SPOT Panchromatic and Multi-Spectral data of the Feb97 and Dec90 render similar results. However, the Division technique on the SPOT Panchromatic does not show as clear as other techniques for the changes of the 3rd run way of the Sydney International Airport. The Subtraction technique of the Panchromatic and the PC1 of the XS123 of the Feb97 and Dec90 provide the best result. An enlarged area of the 3rd Run Way and an area in the South-West of the study are shown in Figure 5. The calculated changed areas (Red color) in the Sydney Metropolitan study area is given as 564.591 sq kilometers.
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| A=SPOT XS321 RGB Dec 1990 |
B=SPOT XS321 RGB Feb 1997 |
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C=Change Detection Subtraction method(PC1XS297-XS1290
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Figure 5. SPOT Multi-Spectral (Dec 90 & Feb 97) of Sydney Airport area with 3rd Run Way clearly
mapped as changed area.
Conclusion
Multi-date temporal SPOT Panchromatic and Multi-Spectral data can be used and easily map changes that took place over the years. The multi-date datasets are required to be rectified and co-registered and is necessary to standardize the atmospheric conditions between the imagery prior to carrying out change detection. Subtraction and division change detection techniques can be applied to detect changes using either single bands or PC1 of the XS1,2 and 3. Subtraction change detection technique of the Panchromatic and the PC1 of the Feb97 and Dec90 provide the best result. Verification of the changes in the field is necessary for accuracy assessment.
References
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Richards, J. A. (1995) Remote Sensing Image Analysis (An Introduction), (2nd Edition), Springer-Verlag Publications, 340 p
