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V L F E L E C T R O M A G N E T I C F I E L D
F I L T E R B A N K S A M P L E D A T A

1. INTRODUCTION

This data set contains power of electromagnetic wave components from
narrow band (10%) filters at 140, 450, 800, 4500, and 15000 Hz. For
any given time segment the power for any one of five predefined pairs
of the five measurable field components (EZ, EH, BZ, BX, BX45) were
measured and are included. The components of electromagnetic field
are named by their direction in the satellite frame.
Spacecraft position in geographic and
magnetic coordinates are also included, along with time and an
indication of which pair of components were measured.
Each data file corresponds to one memory readout, and
typically consists of a few continuous-data segments. The first
several records in each file constitute a header giving the time spans
of the segments, the time resolution, and other common information.
The data records are in ASCII.

Time span of data set: 81-09-30 - 84-07-21
Time span for every file is given in accompany "VLF.TAB" file





2. SHORT DESCRIPTION OF INSTRUMENT

The combined Soviet-French ONCH-TBF onboard instrument (for a
full description see Berthelier et al., Ann. Geophys., v.38, N
5, p.643, 1982) had in memory modes the data only from several
filter-banks in the range from 10 Hz to 16 kHz (while in the
real-time telemetry modes, not presented here, the measurements
included 5-component wave-form data in the range 10 Hz - 1.5 kHz
for 3 magnetic and 2 electric field components, or a wide-band
mode in the range 10 Hz - 15 kHz, and several filter banks).

Thus the BZ (magnetic), and EZ (electric) components are along the
satellite's Z-axis, BX is along the X-axis, BX45 is in the XY-plane
at 45 degrees between the X- and Y-axis, EH is in a plane making an
angle of 18 degrees with the YZ plane and at an angle of 11.5
degrees with the XY plane. This distribution of the measurement axes
was partly due to constraints implied by the satellite construction.

The data presented here are from the ACP filter bank which
included 5 pairs of narrow band (~10%) filters (ACP1-ACP10).
Their center frequencies are given in the Table 1.

Table 1
-------------------------------------------------------------------
Filter : ACP1 and : ACP2 and : ACP3 and :ACP4 and : ACP5 and
: ACP6 : ACP7 : ACP8 : ACP9 : ACP10
-------------------------------------------------------------------
Center
Frequency 140 450 800 4.500 15000
(Hz)
-------------------------------------------------------------------

The name of the electric and/or magnetic field component sampled
by a filter is given by the code F/S. The Table 2 gives the
coding (which is repeated in a data file in each data line.
During a seance it can be fixed (regime "STOP"), or cycling,
changing each 4 seconds in the 16 seconds period in one of the
following sequences: (1,3,2,5) or (1,4,2,5).

Table 2
------------------------------------------------------------------
Code F/S : Field component for : Field component for

: ACP1-ACP5 : ACP6-ACP10
------------------------------------------------------------------
1 EZ BX
2 EH EZ
3 EH BZ
4 EH BX45
5 BZ BX
------------------------------------------------------------------

For the instrument switched off, the F/S = 0.

The data in a file (for a seance) contain the UT time
(hh-mm-ss-mss), the code F/S, the component name, 10 columns
for ELF/VLF wave intensities in the ACP1-ACP10 filters (in
physical units). They are accompanied by the geographic
coordinates (3 columns) and geophysical parameters (invariant
coordinates, etc. - 5 columns).

Please, note that in a data file, the first 1-7 rows usualy give
spurious data due to telemetry and instrument switches and
decoding programs adjustments, AND THUS MUST BE DISCARDED.

3. DESCRIPTION OF COORDINATE SYSTEM FOR THE VLF EXPERIMENT.

The SATELLITE FRAME is: Z-axis along the upward vertical of the Earth's
oriented satellite (within +/- 15 degrees from local vertical in flight),
X-axis along the forward direction ( within +/- 15 degrees from the
velocity vector in flight), Y-axis forming the right-hand frame (to
the left side from the satellite's velocity vector).


4. DESCRIPTION OF FILES AND FORMAT

4.1. Name of files

The filename contains the number of the memory readout seance
followed by the letters "a3a". The file extension is ".DAT".

Each file has a header and number of data records.

Logical record -184 bytes +Cr/LF

4.2. Record Format description


WORD ASCII MEANING UNITS/COMMENTS

1 I4 Hour (0-23)
2 I3 Minute (0-59)
3 I3 Second (0-59)
4 I4 Millisecond

5 F3.0 Code F/S (1,2,3,4,5) Defines the pair
of the electromagnetic field
components measured, see
Table 2.1


6 A3 Electromagnetic field component
measured in the filters ACP1-ACP5 (BX,BX45,BZ,EH,EZ)

7 E11.3 Field Intensity in the Filter ACP1 nT/sqrt(Hz) if BX, BX45,
or BZ; V/m.sqrt(Hz) if EH, or EZ

8 E9.3 Field Intensity in the Filter ACP2 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

9 E9.3 Field Intensity in the Filter ACP3 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

10 E9.3 Field Intensity in the Filter ACP4 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

11 E9.3 Field Intensity in the Filter ACP5 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

12 A5 Electromagnetic field components
measured in the filters ACP6-ACP10 (BX,BX45,BZ,Eh,EZi

13 E11.3 Field Intensity in the Filter ACP6 nT/sqrthHz) if BX, BX45, or BZ;
V/m.sqrt(HЗ) if EH, or EZ

14 E9.3 Field Intensity in the Filter ACP7 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

15 E9.3 Field Intensity in the Filter ACP8 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) if EH, or EZ

16 E9.3 Field Intensity in the Filter ACP9 nT/sqrt(Hz) if BX, BX45, or BZ
V/m.sqrt(Hz) if EH, or EZ

17 E9.3 Field Intensity in the Filter ACP10 nT/sqrt(Hz) if BX, BX45, or BZ;
V/m.sqrt(Hz) Иf EH, or EZ

18 F10.1 Altitude of the Spacecraft km

19 F8.2 Geographic Latitude of the Degrees +/-90
Spacecraft

20 F8.2 Geographic Longitude of the Degrees, 0-360
Spacecraft

21 F8.2 L, McIlwain's Invariant Magnetic Earth's Radii
Drift Shell Parameter

22 F8.2 L0, Invariant Latitude Degrees, +/-90
L0=arc cos (sqrt(1/L))

23 F8.3 BMAG, Module of the MilliGauss
IGRF80 Magnetic Field (1 milliGauss=100nT)

24 F7.2 MLT, Magnetic Local Time Hours.decimal hours
(for centered dipole field)

25 F8.2 ZSUN, Solar Zenith Angle Degrees, 0-180
-----------------------------------------------------
Note. The parameters 15-22 were calculated with
the CADR4 program developed in IKI for orbital and geophysical
reference information for near-Earth satellites (Galperin et
al., Preprint IKI (in Russian), Pr 544, 1980).


5. STRUCTURE OF A HEADER

The header starts with a title:
"PASSPORT FOR THE SEANCE S-XXXX, ARCAD-3". It
gives (in place of XXXX) the number of the memory readout
telemetry seance and the time intervals of the data recording.
The orbit numbers within a seance thus are lower, or equal, to
the seance number.

The first header text paragraph starts with a row "THE NUMBER OF
THE TIME INTERVALS - YY". It gives (instead of YY) the number of
uninterrupted memory recordings, each one in a particular memory
mode ZAP (described in GENERAL.TXT). Each such recording is
described as a line in the "PASSPORT...". Within a data file it
corresponds to a number of lines each describing a "measurement
point" by a line of the data. The number of measurement "points"
(from the start to the end of each recording) is shown in two first
columns of each line, the next columns give the date (dd.mm.yy)
and the UT time (hh.mm.ss.mss) of the start of the interval, then
the same for the end of an interval. The before last column of a
passport row gives the DT - a data time step in milliseconds
(mss), and the last column gives the memory mode ZAP (1-4).

In the second heading paragraph, a reminder is given that
the first rows (up to 7) with the data in each time/ZAP interval
may be false due to telemetry switches, etc., AND THUS MUST BE
DISCARDED.

The third text paragraph in a file heading contains
The emission intensity of the electric (EH,EZ) and magnetic
(BX,BX45,BZ) field components is presented in units V/m.sqrt(HZ)
and nT/sqrt(HZ) respectively. The filters have center
frequencies, respectively, for ACP1 and ACP6 - 140HZ;
ACP2 and ACP7 - 450HZ; ACP3 and ACP8 - 800HZ;
ACP4 and ACP9 - 4.5kHZ; ACP5 and ACP10 - 15kHZ


The NX=ZZZZZ - gives (by ZZZZZ) the total quantity of the
rows in the data file, or the number of the measurement points
registered. Some of them can be erroneous due to telemetry noise,
so the real quantity of the rows can be lower, or equal, to the NX
quantity.

The headings of each data column within a data file are
provided, which contain the meaning of the data in the column
(see Format Description above).

As the date of measurements in a data file for each time
interval is given in the "PASSPORT OF THE SEANCE", it is
not repeated in the data rows, and only the UT is given.