The Equatorial Magnetometer Network Information about J-format

1. Elements of Kyushu University magnetic data
   Fluxgate magnetometer (ring core type)
   Sampling time : 3 seconds.
   component : H,D,Z, 3 components
   

2. How many days data in a disk ?
   The data is recorded on MS-DOS disk with a format called "J- format". A 5 inch floppy disk can store 6 files, and each file contains one day magnetic data. One floppy disk, therefore, stores 6 day data in it.
   

   One disk : 6 files, 6 days data

3. File name
   Each file has a file name, which is composed of 7 characters with a 3 character extension. The first byte should be a letter "r", and the following 6 bytes denote the "YYMMDD". The 3 character extension should be a 3 character abbreviation of a station name. The structure of the "name" is shown as follows.
   

   'r'	1 byte	the first should be " r "
   year	2 byte	ex. 1991 -> 91
   month	2 byte	01 -> January
   day	2 byte	11 -> 11th day
   station	3 byte	ex. bel for BELEM

   File name format : rxxxxxx.xxx

   example --> r910111.bel

4. Structure of the data
   Each file consists of three parts. The first is the "data information" which are written in "text" format. You can read this "text" by "type command" (MS-DOS) or the screen editor. The second is "linkage data", which is described later. The third is the "magnetic data", which is in "binary".
   

   The data = data information ("text") + linkage data ("binary") + magnetic data ("binary")

   The details is as follows.
   

   • Data information : "text"
     This data information consists of,
     

     1.	station name	: Belem
     2.	year	1991
     3.	month	01
     4.	day	11
     5.	local time at the station	LT=-3
     6.	sampling rate	DT=3
     7.	data source	INT(Internal)
     8.	sensitivity of magnetic data H: northward D: eastward Z: vertically downward	6.00e-003 nT/LSB
     9.	memorandum

     In the "memorandum", miscellaneous information are stored. Time correction status, for example, is recorded in this part. The size of the formation is variable. Attention, however, that the information written in this memorandum is of no use for general users. They are stored for internal use only.
     

     An example of the information part is shown in the following.
     

     BELEM 1991 1 11 LT= -3 DT= 3 INT \r\n
     H= 6.00e-003 D= 6.00e-003 Z= 6.00e-003 nT/LSB \r\n
     sdtc 1 26 5 49 -1 -1 \r\n
     sdtc 1 27 5 -1 -1 -1 \r\n
     sdtc 1 27 5 -1 -1 -1 \r\n
     sdtc 1 26 5 -1 -1 -1 \r\n
     sdtc 1 26 5 48 5 -1 \r\n
     sdtc 1 27 1 -1 -1 -1 \r\n
     sdtc 3 28 5 46 5 498 \r\n
     sdtc 3 26 5 48 5 500 \r\n
     sdtc 0 -1 -1 -1 -1 -1 \r\n
     sdtc 0 -1 -1 -1 -1 -1 \r\n
     sdtc 0 -1 -1 -1 -1 -1 \r\n
     ^z\0

     Use (ASCII code 5C) instead of \ (5C).
     \r\n means "return" code of text data file.
     ^z\0 means "end" code of text data file.
     

   • Linkage values : "binary"
     The "linkage values (total 6 bytes)", Lh, Ld and Lz, follow immediately after the "memorandum" with 2 byte integer each. Because the length of the memorandum is variable, the start position of the linkage data is not fixed in the data files. You have to seek for the code " ^z\0" ( ^z\0 = 001A hexadecimal ), which shows the end of memorandum.
     

     The "linkage value" is the difference between the last value of a component on certain day (ie, the value of the component at 23h59m57s on n day, n=1,2,...,365) and the base value of the previous day (ie, the data at 23h59m57s on n-1 day). See Fig.1.
     

     Linkage value(n+1) = last value (23h59m57s on n+1 day) - last value (23h59m57s on n day) [ n = 1,2,3..... ]

   • Magnetic data : "binary"
     Following the linkage data (total 6 bytes), you may find the "magnetic data", which are also "binary". Total number of the data is 86400 data/day (2(bytes) x 86400 bytes, 86400 = 3(comp) x 28800, 28800 = 20 x 60m x 24h data/day)
     They are also the difference between values at each time and that at the last (23h59m57s). See Fig.1.
     

     magnetic data (differential, n day) = each value( h m s, n day) - last value (23h59m57s, n day) [ n = 1,2,3..... ]

[ Structure of data : "Information" + "Linkage" + "Magnetic data" ]

< Information >	. . .
< end of information >	[ 001A H ]
< linkage values, Lh,Ld,Lz >	total 6 byte integer
No.1 magnetic data	[ H comp. ] [ D comp. ] [ Z comp. ]
No.2 magnetic data	[ H comp. ] [ D comp. ] [ Z comp. ]
No.3 magnetic data	[ H comp. ] [ D comp. ] [ Z comp. ]
No.4 - No.28798 magnetic data	: : :
No.28799 magnetic data	[ H comp. ] [ D comp. ] [ Z comp. ]
No.28800 magnetic data	[ H comp. ] [ D comp. ] [ Z comp. ]

[ Fig. 1 ]