(Description based on material from VG2_PRA_JUP_HRES_DS.CAT)
Voyager 2 Radio Astronomy (PRA) data from the Jupiter encounter (1979-04-25 to 1979-08-04).
The data set provides 6 second high resolution lowband radio mean power data. The data
are provided for 70 instrument channels, covering 1.2 to 1326.0 kHz.
This data set (VG2-J-PRA-3-RDR-LOWBAND-6SEC-V1.0) contains
data acquired by the Voyager-2 Planetary Radio Astronomy (PRA)
instrument during the Jupiter encounter. The bounding time
interval set for most Voyager 2 Jupiter PDS data sets is the
Voyager project defined 'far encounter' mission phase boundary
(1979-07-02 to 1979-08-03). Since, however, the PRA instrument
is able to observe planetary phenomenon at much larger ranges
than other fields and particles experiments, this boundary is
artificial with respect to PRA. Hence, PRA lowband data
provided here cover the entire Jupiter Encounter Phase
(1979-04-25 to 1979-08-04). Data from beyond the far encounter
interval is contained in the cruise data archive which is
available from the NSSDC.
VG2-J-PRA-3-RDR-LOWBAND-6SEC-V1.0 contains data at the highest
time resolution possible during normal operations. The normal
mode of PRA operations during the planetary encounters was to
sweep through the two radio receiver bands, high band (40.5 to
1.5 MHz in 128 channels spaced 0.3072 MHz apart) and low band
(1326.0 to 1.2 kHz in 70 channels spaced 19.2 kHz apart) in a
period of 6 seconds. The receivers measured, on alternate
samples, the left hand circular and right hand circular (radio
definition) power.
Measured Parameters
===================
The data here are from the low frequency receiver band and are
'packaged' into spacecraft major frame records. Each major
frame is 48 seconds long or eight sweeps through the PRA
receiver. The data are calibrated and are given in units of
'millibels' which is 1000 times the log of the received power.
Zero millbels corresponds to approximately 1.4 x 10^-21 W m^-2
Hz^-1, however, this value is never seen in practice. The
minimum values detected, which includes receiver internal and
spacecraft generated noise, are about 2300 to 2400 millibels,
or about 3.5 x 10^-19 W m^-2 Hz^-1; even higher values are seen
at the very lowest frequencies.
The data format is ASCII and consists of a time indicator
followed by an array containing the eight low band sweeps. Time
is spacecraft event time (SCET) which is basically universal
time at the spacecraft. Specifically, time is in the form of
YYMMDD and seconds into YYMMDD. Both are written as I6.
Example: July 1, 1979 at 12 hours SCET would be 790701, 43200.
The seconds correspond, to the nearest second, to the start of
the sweep (which occurs in PRA high band). The first value in
low band (1326.0 kHz) occurs some 3.9 seconds after this time
and samples at successively lower frequencies are spaced 0.03
seconds apart. Only one time is given for the entire major
frame, thus the start of each sweep is the time given plus 6
times the sweep number minus 1 (i.e., 0 through 7).
The data array is dimensioned as 71 X 8 and written as I4
format (i.e. 568I4). The '8' corresponds to the eight PRA
sweeps. The lowest 68 of the 70 low band channels (1287.6
to 1.2 kHz) are in positions 2-69. Positions 70-71 should be
ignored. Missing or bad data values are set to zero. In
position 1 of each sweep is a status word where the 12 least
significant bits have used, although not all 12 have meaning
for PRA low band. Numbering those bits 0 for least significant
to 11 for most significant, the bits that have meaning are as
follows:
bit
0: 15 dB attenuator in use when equal to 1
1: 30 dB attenuator in use when equal to 1
2: 45 dB attenuator in use when equal to 1
9,10 (together): polarization of first channel sampled (1326.0
kHz) according to the scheme:
+---------------------------+
| | |value bit|
| | | 10= |
| | | 0 | 1 |
|value bit 9=| 0 | R | L |
| | 1 | L | R |
+---------------------------+
Polarization at successively lower frequencies is opposite to
the frequency above it, i.e. either a LRLR or an RLRL pattern.
Successive 6-second sweeps start on the opposite polarization
as the previous sweep as indicated in the status bits. Note
that this polarization is the received polarization, not
necessarily the emitted polarization. Correct interpretation of
the received polarization depends on the antenna plane
orientation relative to the radio source. A good description of
this concept can be found in Leblanc Y., Aubier M. G., Ortega-Molina A.,
Lecacheux A., 1987, J.Geophys. Res. 92, 15125 and in Wang, L. and Carr, T.D.,
Recalibration of the Voyager PRA antenna for polarization sense
measurement, Astron. Astrophys., 281, 945-954, 1994. and references therein.
Missing or bad data values are set to zero. If the status word
is zero, any data in that receiver sweep should be discarded.
Data Coverage
=============
The data are stored as 4 ASCII tables (.TAB), each accompanied with a PDS
label file (.LBL) which describes properties of the data file. Data
cover the following time intervals:
Volume ID: VGPR_1201
+-------------------------------------------------------------------------+
| Filename |Records| Start | Stop |
|-------------------------------------------------------------------------|
| PRA_I.TAB | 32707| 1979-04-25T00:00:04.000Z |1979-05-28T23:59:14.000Z |
| PRA_II.TAB | 34207| 1979-05-29T00:00:02.000Z |1979-06-23T23:59:59.000Z |
| PRA_III.TAB| 31652| 1979-06-24T00:00:47.000Z |1979-07-12T23:59:58.000Z |
| PRA_IV.TAB | 34416| 1979-07-13T00:00:46.000Z |1979-08-04T23:05:33.000Z |
+-------------------------------------------------------------------------+
Confidence Level Overview
=========================
The accuracy of calibration in the PRA low band is
approximately 2 dB, except at frequencies below 100 kHz where
it is somewhat worse. Interference from the Voyager power
subsystem is a major problem to the PRA instrument, affecting
many of the 70 low band channels. This interference manifests
itself by abrupt changes in background levels. Some channels,
notably 136 and 193 kHz, are almost always affected, whereas,
others are only affected for short intervals. Usually, this
interference is only a problem when the natural signals are
weak.
Additional information associated with this data set is available in the
following files:
+------------------------------------------------------------------------------------------------------------------------------------------+
| file | contents |
|------------------------------------------------------------------------------------------------------|-----------------------------------|
|https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VGPR_1201/CATALOG/VG2_PRA_INST.CAT | VG1 PRA instrument description |
|https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VGPR_1201/CATALOG/VG2_PRA_JUP_HRES_DS.CAT | data set description |
|https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VGPR_1201/CATALOG/PERSON.CAT | personnel information |
|https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VGPR_1201/CATALOG/REF.CAT | key reference description |
|https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VGPR_1201/DOCUMENT/INSTRUMENT | ASCII and HTML versions of the PRA|
| | investigation description paper |
+------------------------------------------------------------------------------------------------------------------------------------------+