TOPIST ---- ERROR CODE NUMBERS AND EXPLANATIONS
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001 NOT A USABLE DATA FILE - INVALID SATELLITE ID NUMBER FOUND
       (Valid value=1, 2, 3, or 4)
002 NOT A USABLE DATA FILE - INVALID TRANSMITTER CODE FOUND
       (Valid code=1 or 2) 
003 NOT A USABLE DATA FILE - INVALID RECEIVER CODE FOUND
       (Valid code=0 or 1)
004 NOT A USABLE DATA FILE - INVALID FREQUENCY RANGE CODE FOUND
       (Valid code=0 or 1)
005 NOT A USABLE DATA FILE - INVALID DMODE CODE FOUND
       (Valid code=0 or 1)
006 NOT A USABLE DATA FILE - INVALID GMODE CODE FOUND
       (Valid code=0 or 1)
007 NOT A USABLE DATA FILE - INVALID SOUNDER MIXED MODE FOUND
       (Valid code=0 or 1)
008 NOT A USABLE DATA FILE - INVALID AIT MODE FOUND
       (Valid code=0 or 1)
009 NOT A USABLE DATA FILE - INVALID FIXED FREQUENCY CODE FOUND
       (Valid code=0, 1, 2, 3, 4, 5, or 6)
010 NOT A USABLE DATA FILE - NEGATIVE FREQUENCY MARKS FOUND
       (All frequency marks should be a positive number)
011 NOT A USABLE DATA FILE - STARTING SWEPT FREQUENCY > 0.1MHz
       (Starting swept frequency should be 0.1MHz)
012 NOT A USABLE DATA FILE - NON-MONOTONIC FREQUENCY MARKS FOUND
       (The frequency marks should increases monotonically)
013 NOT A USABLE DATA FILE - FREQUENCY MARKS NOT WELL DEFINED
       (There are large gaps among frequency marks) 
018 NOT A USABLE DATA FILE - DATA ERROR FOUND
       (An unidentified data error)
019 NOT A USABLE DATA FILE - THE FILE IS NOT COMPLETE
       (The end of file reached without enough data blocks as the file declared)
020 DATA ERROR FOUND OR THIS FILE IS NOT IONOGRAM DATA
       (The data format are found completely acceptable and the file is most 
       likely not an ionogram data file)