How is landscape change analysis performed with satellite imagery?
Sun-synchronous satellites return to the same point on the face of the Earth at a regular time each day. Multiple images of the same location can be compared to each other to statistically extract changes. When images are analyzed over seasons, it is possible to examine the phenology of the landscape. When anniversary dates of imagery are examined, human and natural landscape changes can be extracted. Change detection is usually accomplished by subtracting the images or performing correlation analysis to determine differences. Digital images are roughly analogous to spreadsheets. The individual cells contain numbers which can be subtracted, divided, or otherwise manipulated. By subtracting two images, the areas of change can be highlighted. It should be noted that there are several ways of highlighting areas of change, or creating change masks, ranging from very simple to very complex processes involving correlation analysis.
