Imagery from ERTS or the Synchronous Meteorological Satellites, because of its precisely repetitive nature, is ideally suited both for subjective enhancement via time-lapse display and for objective measurements of changes with time. The SRI ESIAC, a hybrid system providing both viewing and image processing functions, is described. A representative application involves the measurement of changes in aerial extent of snow cover within specified mountain watersheds.

Subjective viewing of time-lapse sequences of the snow scenes provides valuable insight into the nature of numerous extraneous signals, permitting the interim implementation of operationally useful snow measuring systems while hopefully leading toward the design of fully objective classifiers.

A short movie of selected ERTS time sequences will be shown to illustrate the concepts discussed.

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