SeaWiFS Project - LEVEL 0 OUTPUT FILE FORMAT FRAME FORMATTER (LEVEL 0) OUTPUT FILE FORMAT Version 1.1 Frederick S. Patt April 16, 1993 Updated May 1996 - see below SUMMARY DESCRIPTION: The SeaWiFS Frame Formatter (FF), developed and maintained by the Data Capture Facility (DCF), will produce one output file for each data transmission. This will be either a recorded data file, with GAC and LAC segments interleaved, output twice per day according to the data dump schedule; or a real-time LAC file, output up to three times per day according to the SeaStar/GSFC direct broadcast schedule. Real-time LAC will be de-crypted by DCF prior to processing by the FF. The FF output file will be first generated on a local disk and then copied to a disk file on an SDPS computer where it will be reformatted as described below. The file will consist of a 512-byte header followed by a number of data records. Each record will contain a single minor frame regardless of source and format. All 10-bit telemetry words will be right-justified in 16 bits and the 8-bit words will be output as such. The synchronization words will be stripped off. The records are padded to an integer number of 512-byte blocks, with a record length of 21 Kbytes. The FF will output only complete minor frames to the file; frames which are incomplete due to data dropouts or loss of bit synch will be rejected and no fill frames will be generated. A count of the number of lost minor frames will be included in the header file. The FF also estimates the bit error rate for each frame using the trailing synch words, and this information will be included in the quality flags at the beginning of each record. DETAILED FORMAT SPECIFICATIONS FILE HEADER BYTE(512) FF OUTPUT FILE HEADER (Includes number of lost frames and start and end times of data receipt at DCF; format is TBD.) -------------------------------- TOTAL HEADER LENGTH = 512 BYTES RECORD FORMAT INTEGER*2 FF QUALITY FLAG 1: NUMBER OF SYNCH BITS USED FOR ERROR RATE BYTE FF QUALITY FLAG 2: NUMBER OF BIT ERRORS IN SYNCH BITS INTEGER*2(2) SPACECRAFT ID (10-BIT SPACECRAFT WORDS RIGHT-JUSTIFIED IN 2 BYTES) INTEGER*2(4) SPACECRAFT TIME TAG (10-BIT SPACECRAFT WORDS RIGHT-JUSTIFIED IN 2 BYTES) BYTE(775) SPACECRAFT STATE-OF-HEALTH TELEMETRY (8-BIT WORDS); IN LAC THIS SUBCOMMUTATES REAL-TIME SPACECRAFT SOH, BACK-ORBIT SPACECRAFT SOH AND OX.25 SUBPACKET INTEGER*2(10356) SEAWIFS DATA (10-BIT SPACECRAFT WORDS RIGHT-JUSTIFIED IN 2 BYTES) LAC FORMAT: 44 WORDS; THIS FIELD SUBCOMMUTATES INSTRUMENT TLM AND ANCILLARY TLM PACKETS 8 WORDS GAIN AND TDI 10304 WORDS LAC SCAN LINE GAC FORMAT: 10080 WORDS: 5 GAC SCAN LINES @2016 WORDS 220 WORDS: 5 INSTRUMENT/ANCILLARY TELEMETRY PACKETS @44 WORDS 56 WORDS SPARES BYTE(2) SPARES (to fill out to 21 kbytes) -------------------------------- TOTAL RECORD LENGTH = 21504 BYTES = 21 KBYTES Update to the SeaWiFS Level 0 Frame Format - September 1997 B. Franz SeaWifs File Header The SeaWifs Level-0 file begins with a 512 byte header block. Most of this header is not used, and can therefore be filled with zeros. In this update to the format specification, several fields have been eliminated. Only those fields which are currently used or likely to be used in future releases of L1agen have been retained. field size -bytes- type 1 5 000 004 char[5] - characters "CWIF\0". These characters are invariant. 2 1 005 005 char - if = 0 then this is a LAC/GAC File, if = 1 then this is an HRPT File. 3 4 316 319 long - Number of aux and/or sync bits examined for bit error calculation. 4 4 320 323 long - Number of bit errors found in auxsync or framesync fields. 5 4 332 335 time_t - Acquisition start time (AOS) in seconds since Jan 1, 1970 00:00, 4-byte integer. 6 4 336 339 time_t - Acquisition end time (LOS) in seconds since Jan 1, 1970 00:00, 4-byte integer. SeaWiFS Project Home Page gene carl feldman (gene@seawifs.gsfc.nasa.gov) (301) 286-9428