DIGITIZING SATELLITE IMAGERY - QUALITY AND COST CONSIDERATIONS

The recent declassification of major U.S. satellite reconnaissance pro grams offers a significant source of imagery to the civil community. W ith nearly two billion square kilometres of coverage collected over a 12-year period, a rich database of imagery will become available to en vironmental researchers, archaeologists, historians, and other users o f archived imagery. Imagery collected by the CORONA, ARGON, and LANYAR D systems pre-dates Landsat and Earth Resources Technology (ERTS) cove rage and, thus, extends the historical archive of satellite imagery by 12 years. Unlike Landsat and ERTS imagery, however, the CORONA/LANYAR D/ARGON imagery was collected with film-return systems. For many poten tial applications, it will be desirable to place the data in digital f ormat. This will require digitizing the film records. The National Exp loitation Laboratory recently completed a study designed to determine the impact of digitizing resolution on the information content of the resultant digitized products. A sample of imagery (duplicate positives ) was digitized with a sample of digitizers at various digitizing spot sizes. The digitized data were displayed in softcopy, and imagery ana lysts compared the softcopy images to the original hardcopy products. Information loss was measured in terms of the National Imagery Interpr etability Scale (NIIRS). Results of the study provide the basis for se lection of digitizer resolution as a function of information/bandwidth trade offs. A brief assessment of relative costs as a function of dig itizer resolution was also made.