The resolution of a sensor system can be defined as its ability to discriminate information. This general concept includes several aspects that deserve detailed discussion. On the one hand, the resolution of a sensor refers to the system as a whole instead of its individual components. On the other hand, discrimination refers to the ability of the sensor to distinguish a specific object from other objects. This process may simply determine that the object is there (detection) or it may imply as well a precise delimitation of its shape (identification). Obviously, the latter task requires a higher spatial resolution than the former (Robin 1998). For instance, an object can be detected through its effect on the observed global radiance, such as an abrupt increment in temperature due to a volcanic eruption, but in order to identify and characterize the volcanic crater itself, the sensor should be able to resolve objects much smaller than the crater size.