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The data on the CD-ROM are coded as 32-bit (long integer) binary words, with 5888 words comprising a day- long record. Each file contains one month of day records.
| Words 1-10 | contain header information including a 3-letter observatory
identification (ID) code, the year concatenated with the day of the year,
co-latitude, longitude, elevation, orientation, originating organization,
a D-conversion factor, data quality, and instrumentation. The D-conversion
factor is a fixed value used only in the graphics portion of the access
software to allow Declination to be plotted in minutes of arc and equivalent
nanoteslas (nT). It is given as H/3438*10000, where H is the annual mean
value of the horizontal intensity.
ASCII values, such as the observatory ID and orientation, are also stored as 32-bit words, but are coded as the hexadecimal byte-string corresponding to the ASCII string. For example, the string "HDZF" is coded as the sequence "48 44 5A 46". |
| Word 11 | K-9 value for observatory in nT |
| Word 12 | is digital sampling rate in msec |
| Word 13 | is sensor orientation. Sensor orientation could by XYZF, DIF, UVZ, HDZ, HDZF etc. It should indicate which components are actually measured |
| Words 14-16 | are reserved for future use and padded with zeros. |
| Words 17-5776 | contain the minute values of the 4 components (successively H,D,Z,F or X,Y,Z,F) for the day. The values are stored in tenth- units with an implied decimal point. Thus, an H value of 21305.6 is stored (in tenth-nT) as 213056 with a decimal point implied between the last and next-to-last digits. |
| Words 5777-5872 | are used for the hourly mean values of the successive 4 components. |
| Words 5873-5876 | store the 4 daily mean values. |
| Words 5877-5884 | hold the 8 K- Index values for the day. |
| Words 5885-5888 | set aside for each contributing institution to use as they wish, provided it is coded as a 32-bit binary value. |
Missing data for minute, hour, and day values are stored as "999999". Missing K-Index are stored as "999".
Each 1-day record requires 23,552 bytes, so a month-file for January would require 730,112 bytes of storage. A year of observatory data requires almost 8.6 Megabytes (Mb) of memory, so the 41 observatories on the 1991 INTERMAGNET CD-ROM require more than 352 Mb of storage space. The storage capability of a CD-ROM is about 640 Mb, which implies an upper limit for a single CD-ROM of about 74 observatory years of data. Actually, due to the addition of README files, screen images, map images, etc., this figure is closer to 65 observatory years. The actual size of the 1991 CD-ROM is 354,992,128 bytes in 607 files and 47 directories.
| HEADER | Word 1 | Station ID | eg. BOU |
|---|---|---|---|
| 2 | Year || Julian Day | eg. 1989001 ; January 1, 1989 | |
| 3 | Co-Latitude | (90° - Latitude) * 1000 | |
| 4 | Longitude | East Longitude * 1000 | |
| 5 | Elevation | elevation in metres above sea level | |
| 6 | Orientation | HDZF or XYZF | |
| 7 | Origin | eg. USGS, GSC, BGS,EOPG etc. | |
| 8 | D Conversion | H/3438*10000 where H=annual mean of H | |
| 9 | Data Quality | IMAG | |
| 10 | Instrumentation | eg. RC (Ring Core), LC (Linear Core), etc. | |
| 11 | K-9 Value in nT | e.g. 750 | |
| 12 | Digital Sample Rate (ms) | e.g. 125 | |
| 13 | Sensor Orientation | e.g. XYZF, HDZF | |
| 14 | RESERVED FOR FUTURE USE | ||
| 15 | |||
| 16 | |||
| ONE MINUTE DATA |
17 | 1440 minute mean values - element 1 (one day) | |
| ... | |||
| 1456 | |||
| 1457 | 1440 minute mean values - element 2 (one day) | ||
| ... | |||
| 2896 | |||
| 2897 | 1440 minute mean values - element 3 (one day) | ||
| ... | |||
| 4336 | |||
| 4337 | 1440 minute mean values - element 4 (one day) | ||
| ... | |||
| 5776 | |||
| MEAN HOURLY DATA |
5777 | 24 mean hourly values - element 1 (one day) | |
| ... | |||
| 5800 | |||
| 5801 | 24 mean hourly values - element 2 (one day) | ||
| ... | |||
| 5824 | |||
| 5825 | 24 mean hourly values - element 3 (one day) | ||
| ... | |||
| 5848 | |||
| 5849 | 24 mean hourly values - element 4 (one day) | ||
| ... | |||
| 5872 | |||
| DAILY MEANS |
5873 | daily mean value - element 1 | |
| 5874 | daily mean value - element 2 | ||
| 5875 | daily mean value - element 3 | ||
| 5876 | daily mean value - element 4 | ||
| K INDICES |
5877 | 8 digitally derived K Indices | |
| 5878 | |||
| 5879 | |||
| 5880 | |||
| 5881 | |||
| 5882 | |||
| 5883 | |||
| 5884 | |||
| 5885 | Reserved for each contributing institution | ||
| 5886 | |||
| 5887 | |||
| 5888 | |||
The files on the INTERMAGNET CD-ROM are set up in a particular directory structure. The root directory contains a "README.TXT" file, which is an ASCII file describing the CD-ROM and where to obtain information about it, the software, and documentation; and a "README.EXE" file, which is an executable version of the README.TXT file that allows the user to scroll back and forth through the information.
On the 1991 CD-ROM there are also two sub-directories. One is labelled "XTRAS", and the other "MAG1991". The XTRAS directory contains one file labelled "STRUCTUR.DAT", and another "PRNSTRUC.EXE". The STRUCTUR.DAT file provides a schematic of the data structure for the records on the CD-ROM and the PRNSTRUC.EXE file enables the user to obtain a printout of that record structure.
The MAG1991 directory contains a sub-directory for each observatory identified by its 3-letter ID code. In addition, there are sub-directories labelled "1991MAPS", "CTRY_INF", and "OBSY_INF". The 1991MAPS directory contains the *.PCX files that are the map images of each country for use in the access software. These are labelled by a 3-letter country ID with the PCX extension, and one labelled "ALL.PCX" for the "All Countries" option. The CTRY_INF directory contains a "CTRYLIST.IDX" file that is used internally, *.PCX files for each country (and one for ALL) that are the images used to show the flag and organizational Logo for the different countries, and the README files that pertain to each country's geomagnetism program (including a README for the ALL option). The OBSY_INF subdirectory contains a "91OBSYDAT.DBF" file that is used internally in the software.
The individual sub-directories (e.g. BFE for Brorfelde, TUC for Tucson, etc.) contain the 12 months of data labelled with the 3-letter ID, 2-character year, 3-letter month abbreviation, and a "BIN" extension indicating they are binary files. For example, "BFE91AUG.BIN" is a file of 31 sequential day-records for Brorfelde, for 1991, for August. In addition, there are the "README.XXX" files for the individual observatory, where the XXX indicates the 3-letter observatory ID.
For those observatories that provided an ASCII K-Index file, this sub-directory also contains that file labelled as XXXYRK.DKA, where the XXX is the 3-letter observatory ID, the YR is the 2-character year value, the K indicates a K-Index file, and the DKA extension indicates that the data were generated from a digital algorithm and is an ASCII file. These K-Index files are used, even though the data are in the binary records, because they are much faster to access than paging through the binary records on the CD-ROM.
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Comments:webmaster 2002-04-04 jp ©2002 INTERMAGNET |