Luttrell S P and Oliver C J, 1985, Prior knowledge in synthetic aperture radar (SAR) processing, in RSRE Research Review (, RSRE, ed. Grant A J, Jakeman E, and Clarke J), pp. 73-77
All that we know of the world about us has been deduced from data collected by our senses (eyes, ears, etc), and those of our ancestors. Usually we employ sophisticated transducers (microscopes, telescopes, radars, etc) to transform signals into a form which our senses can 'see', therefore we require an accurate model of the transducer(s) if we are to know how our sensory data is acquired. Furthermore we require a model of the source of the signals being transduced in order to 'make sense of' this data. We shall call this model 'prior knowledge', because it exists in advance of acquiring the data. Such prior knowledge manifests itself with various degrees of complication. In some cases the model may leave very little undetermined, and it remains to determine the values of a finite umber of parameters from the data. This type of situation arises when we take measurements of a well known and controlled phenomenon. In other cases the model may provide only a weak constraint on the source of the signal. This may be for two basic reasons: we are ignorant of what we are observing, or we have a detailed model but it contains a large number of parameters. It could be argued that these are the same reason! In all cases however the model is essential if the data is to be interpreted at all.