Land cover change detection is necessary for updating land cover maps and the management of natural resources. The change is usually detected by comparison between two multi-date images, or sometimes between an old map and an updated remote sensing image.
The method of change detection is divided into two;
a. comparison between two land cover maps which are independently produced
b.change enhancement by integrating two images into a color composite or principal component
image.
Figure 12.2.1 shows the changes over a 5 year period, which were detected by using a color composite with blue assigned to an old image of Landsat TM and red assigned to a new image of Landsat TM.
Such detection is very useful for updating "vegetation maps" of 1:50,000 to 1:100,000 scale with Landsat TM or SPOT, and of 1:250,000 scale with Landsat MSS.
The land cover change can also be divided into two;
a. seasonal change
agricultural lands and deciduous forests change seasonally
b. annual change
land cover or land use changes, which are real changes, for example deforested areas or newly built towns.
Usually seasonal change and annual change are mixed within the same image. However only the real change should be detected, so that two multi-data images of almost same season should be selected to eliminate the effects of seasonal change. One should note that a cycle of seasonal change can be rather complex as shown in Figure 12.2.2. Sometimes seasonal change rate is very high, for example in spring time in cold area.
Copyright © 1996 Japan Association of Remote Sensing All rights reserved