   << Description of Akebono VLF-MCA in Science Database Format >>>

                                        Sep. 15, 1996 (Version 3.01)

The MCA which is one of subsystems of the VLF instrument onboard Akebono 
provides one component of electric field and one component of magnetic field 
at 16 frequency points. The center frequency for each channel is 

	3.16  Hz, 5.62  Hz, 10.0  Hz, 17.8  Hz,
	31.6  Hz, 56.2  Hz, 100.  Hz, 178.  Hz,
	316.  Hz, 562.  Hz, 1.00 kHz, 1.78 kHz,
	3.16 kHz, 5.62 kHz, 10.0 kHz, 17.8 kHz

with a band width of 30% of each center frequency.

The file name of VLF-MCA is given as 'yymmddhh.vlf'.

The file is composed of a series of blocks, each of which 
consists of 496bytes.

The first block is the header whose format is :

 0----+----1----+----2----+----3----+----4---(...)----
  yymmddhhmmss YYMMDDHHMMSS VLF-MCA Ver.3.01 

    yymmddhhmmss: Start date and time (UT) 
                    at the 1st record of the 2nd block (ASCII)
    YYMMDDHHMMSS: End   date and time (UT) 
                    at the last record of the last block (ASCII)
    Ver.3.01    : Version Number

The blocks following the 1st block are the VLF wave data.
One block datum consists of block number (1byte) and 15 records 
(1record = 33bytes), each of which is corresponding to every 
8sec interval (1block = 1 + 33*15 = 496bytes).
Therefore each data block is constructed as follows:

    byte   |  contents    | Elapsed time
 ----------------------------------------------------------------
         1 | block number | (NO)
   2 -  34 |   1st record | yymmddhhmmss + NO*120(sec)
  35 -  67 |   2st record | yymmddhhmmss + NO*120(sec) +   8sec
  68 - 100 |   3rd record | yymmddhhmmss + NO*120(sec) +  16sec
     :     |      :       |
 464 - 496 |  15th record | yymmddhhmmss + NO*120(sec) + 112sec

Each record consists of E and B field intensities of 8sec average 
at 16 frequency points (from 1st to 32th byte) and flags (33th byte)
for observation status.
The 8sec average is taken for an interval from 4sec before 
to 4sec after the elapsed time. E and B intensity data and flags are 
represented by 1byte integer (I) with no sign bit as follows:

    byte   |  contents    
 ----------------------------------------------------------------
   1 -  16 |   E-field    (3.16Hz, 5.62Hz, ..., 17.8kHz)
  17 -  32 |   B-field    (3.16Hz, 5.62Hz, ..., 17.8kHz)
        33 |   Flags for observation status 

The intensities are described in [dB] (0<I<254) where
0[dB]=10^-6[mV/m] for E-field and 0[dB] = 10^-6[pT] for B-field.
The unit byte is filled by I=255 for each data point where data are not 
available. 

The contents in the flag byte are as follows:

  (Upper)  8-3: Blank
             2: BDR (0: OFF 1: ON) *1
  (Lowest)   1: SMS (0: OFF 1: ON) *2

    *1 BDR (Bubble Data Recorder onboard Akebono)
        When the BDR is on (both in record and reproduce mode), 
        interference at harmonics of 32Hz is involved in the VLF data.

    *2 SMS (Superthermal ion mass spectrometer)
        When the SMS instrument is on, impulsive noise interferes
        with the VLF instrument.

    !!!! Note that the interference by BDR or SMS is *not* yet removed 
         from the VLF-MCA data !!


***********************************************************************
  To use the data for any purpose, you are requested to contact 
  the VLF PI, Iwane Kimura. Before you give a presentation 
  in meetings or publish a paper using VLF-MCA data, please 
  send a copy of the abstract or paper to PI:

   PI: Iwane Kimura,
         Dept. of Information System, Osaka Institute of Technology,
         Kitayama, Hirakata 573-01, Japan
         Phone: +81-720-66-5402
         FAX  : +81-720-66-8499
         E-mail ikimura@is.oit.ac.jp

   For further information, please contact with:

       Yoshiya Kasahara,
         Graduate School of Electronics and Communication, Kyoto University,
         Sakyo-ku, Kyoto 606-01, Japan
         Phone: +81-75-753-4983
         FAX  : +81-75-751-8201
         E-mail : kasahara@kuee.kyoto-u.ac.jp

Reference 

Kimura, I., K. Hashimoto, I. Nagano, T. Okada, M. Yamamoto, 
T. Yoshino, H. Matsumoto, M. Ejiri, and K. Hayashi,
  VLF Observations by the Akebono (EXOS--D) Satellite,
  J. Geomagn.  Geoelectr., 42, 459-478, 1990.

Hashimoto, K., I. Nagano, M. Yamamoto, T. Okada, I. Kimura,
H. Matsumoto, and H. Oki,
  EXOS-D (AKEBONO) Very Low Frequency Plasma Wave Instruments (VLF),
  IEEE Trans. Geoelectr. and Remote Sensing, in print, 1996.

-------------------------------------------------------------------------
  SAMPLE PROGRAM (Program consists of 2 parts written in C and FORTRAN)
   (for use on SUN)

---(Part 1 : C language)---
#include        <stdio.h>
#include        <stdlib.h>

FILE            *fp;
unsigned char   buf[496];

opnrmca_(file, l)
char    *file;
int     l;
{
        register unsigned char  *p = buf;
        register int            i;

        if ((fp = fopen(fs2cs(file, l), "r")) == NULL) {
                perror(file);
                exit(1);
        }
}

clsrmca_()
{
        fclose(fp);
}

gtmchd_(head, ver, stm, etm)
double  *stm;
double  *etm;
char    head[10], ver[10];
{
        char astm[15], aetm[15];
        fseek(fp, 0L, 0);

        fread(buf, sizeof(*buf), sizeof(buf), fp);

        sscanf(buf, "%s %s %s %s", astm, aetm, head, ver);
        *stm=atof(astm);
        *etm=atof(aetm);
}


int irdblkm_(iblock)
long    *iblock;
{
        register unsigned char  *p = buf;
        register int            i;

        if (fread(buf, sizeof(*buf), sizeof(buf), fp) == 0)
                return(-1);

        for (i = 0; i < 496; i++) {
                *iblock++ = *p++;
        }
        return(0);
}

---(Part 2 : FORTRAN language)---
      implicit real*4(a-h,o-z),integer*4(i-n)
      character*20 file
      character*10 head, ver
      real*8       stm, etm

      narg = iargc(0)
      if(narg.le.0) then
        write(0,1000)
 1000   format('Usage: rdmca filename(yymmddhh.vlf)')
        call exit(1)
      end if

      call getarg(1,file)
      call opnrmca(file)

      call gtmchd(head, ver, stm, etm)
      print*, 'head=', head, ' ', ver, stm, etm

      call readmca
      call clsrmca

      stop
      end

************************************************************************
      subroutine readmca
************************************************************************
      implicit real*4(a-h,o-z),integer*4(i-n)
      parameter (nwrd =  496)
      parameter (nblk =   90)
      common /mcadata/ iblock(nwrd,nblk), num

      num = 1
    1 continue
      irc = irdblkm(iblock(1,num))

      if (irc.ne.0) goto 999

      num = num + 1
      goto 1

  999 continue

      num = num - 1
      return
      end