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The archival of base data was complicated by the large volume of information needed to be stored. Figure 2.1 below shows a schematic of the base data archival process before the CRAFT project’s introduction of real-time delivery of Level II data. The new archival process for real-time data is discussed in Section 2.2.
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| Figure 2.1NCDC pre-CRAFT archival procedure for WSR-88D Level II data [Droegemeier 00] |
The process begins when a radar site mails a set of ten 8 mm tapes to the NCDC. Each tape may contain up to 4.8 gigabytes of data. The data are then merged and compressed, at a rate up to 10:1, to another archive tape (IBM 3590) for long-term storage. The original 8 mm tapes are then recycled.
On average, the National Climatic Data Center (NCDC) receives 165 gigabytes of base data each day, or approximately 60 terabytes annually. By late 1999, the NCDC had archived some 42,000 8 mm tapes. The base data archive for all 120 NWS radars was 64.9% complete, in comparison to 35.7% and 9.5% for the Department of Defense and Federal Aviation Administration radars, respectively.
The slow speed of the 8 mm tape drives significantly lengthens the time needed to access the base data. Therefore, an order for even a modestly large data set involving a dozen radars may take a few months to be processed and the cost for the data can run into hundreds of thousands of dollars. Furthermore, no mechanism presently exists to peruse the base data and the cost to maintain the now outdated tape system exceeds $0.75M per year. As a result, the low usage of base data does not reflect a lack of interest, but rather a lack of cost-effective access.