Results of a pilot project whereby WWSSN seismic records, originally recorded on film, were digitized.
The USGS WWFC Pilot Scanning Project
The World Wide Standardized Seismograph Network (WWSSN) began operations in 1961. One hundred twenty stations were installed, covering every continent. A station consisted of 3 short-period and 3 long-period seismometers, recording apparatus, radio-synchronized crystal clock, and calibration controls.
Data were originally recorded on photographic paper, then later on heat sensitive paper. The original records were photographed at the WWSSN Data Center using 70 mm film and stored by station and year on a 70 × 120 mm film chip. Lamont-Doherty Earth Observatory and the USGS Albuquerque Seismological Laboratory (ASL) each hold near-complete film chip sets of the WWSSN data. The slow degradation of these film chips has prompted this pilot project in 1999.
The film chips are black and white and have been digitally scanned with a resolution of 3200 dpi. The image has been cropped to exclude areas on the film chip which do not contain the image of the original record, however in all cases, the final product contains all of the original photographed record. The resulting grey-scale images have been saved at approximately 1/10th of the original film chip size as TIF files and then compressed using gzip. Enlarging the images by a factor of 10 results in images similar in size to the original analog record.
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