Introduction
"In the chapters before we only treated advective changes in nowcasting and found some quite useful methods. But cloud systems are not only moving they are also changing their shape because of new development or dissolution of cloudiness. In this chapter we want to look if there are some methods to get information of non-advective changes. Do you have some ideas how to approach?"
"Well, if I look into two consecutive images I see both: the displacement of the cloud systems as well as the changes. If we could compute the difference of the two images, then we would know if the cloud system has increased or decreased."
"Your principal approach is good but you have to take into account that a pure difference of two consecutive images would also include the advective changes. We must separate between the advective and the non-advective part. What we compute are so-called motion corrected images; we call them deviation images.
In the next chapter you find the basic idea behind such a method. The application of such methods is different in different institutes. This is the methods used at ZAMG but what you should learn from this exercise is the principal idea of treatment.
For now, let's look at deviation image computation in more detail!"