SDF Files

The SDI hardware converts the serial data and clock to 32-bit parallel words and stores them in an 8K by 32-bit FIFO. When 4,096 words have been collected, the ingestor software transfers 4,096 words to an SDF file in the ingestor's hard drive. Sixty-four transfers are required to build a 1,048,576 byte (1 Mbyte) SDF file. Thus, each SDF contains 8,388,608 satellite data bits.

Data Storage Requirements

To determine the number of seconds per SDF, divide 8,388,608 by the satellite's bit rate. For example, GVAR's data rate is 2,111,360 bits per second. Therefore, each SDF provides 3.973 seconds of data storage (8,388,608/2,111,360=3.973). At this rate, 906 SDFs are generated per hour.

The data in each SDF file includes all data types sent. Nothing is stripped out and there are no byte aligned boundaries. Thus, new data blocks can start anywhere in any SDF word.

SDF File Naming Convention

SDF files are named using the following convention.

signal_type.ccyy.ddd.hhmmss

Where:

signal_type	is the satellite signal type, e.g., gvar, poes, etc.
cc	is the century when the file was written to disk
yy	is the year when the file was written to disk
ddd	is the julian day the file was written to disk
hh	is the UTC hour the file was written to disk
mm	is the minute the file was written to disk
ss	is the second the file was written to disk

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