The execution of these observations involves intervention by a resident astronomer. The result of the first observation has to be evaluated on the basis of the specified observer requirements. An image of a certain area is to be taken only if a first image, taken at the position of the expected brightness maximum, yields a positive detection. A proposal requesting linked observations has to have a strong scientific case and to contain clear and quantitative specifications of the condition under which the second observation should be carried out. For scheduling reasons the second observation will be carried out at least three revolutions later.
Current experience shows that the linked-observation facility is used very little .
Thus, consideration is being given to deleting it from the ISO system. Proposals requesting linked observations are discouraged. However, should proposers feel that linked observations are essential for their programmes, a very strong scientific justification is required.