PDS3_DATA_SET_ID = VG1-S-PRA-3-RDR-LOWBAND-6SEC-V1.0
DATA_SET_NAME = VG1 SAT PRA CALIBRATED HI-RES LOW FREQ.
REC. BAND DATA V1.0
START_TIME = 1980-11-11T22:09:23.000
STOP_TIME = 1980-11-16T23:59:47.000
ORIGINAL_DATA_SET_RELEASE_DATE = 1996-06-01
PRODUCER_FULL_NAME = MICHAEL L. KAISER
REFERENCES:
Leblanc, Y., M.G. Aubier, A. Ortega-Molina, and A. Lecacheux, Overview of the
Uranian Radio Emissions: Polarization and Constraints on Source Locations,
J. Geophys. Res., Vol. 92, p.15125, 1987.
Warwick, J.W., J.B. Pearce, D.R. Evans, T.D. Carr, J.J. Schauble, J.K.
Alexander, M.L. Kaiser, M.D. Desch, M.Pedersen, A. Lecacheux, G. Daigne, A.
Boischot, and C.H. Barrow, Planetary Radio Astronomy Observations from
Voyager 1 Near Saturn, Science, Vol 212, p. 239-243, 1981.
DATA_SET_DESCRIPTION
Data Set Overview
=================
This data set (VG1-S-PRA-3-RDR-LOWBAND-6SEC-V1.0) contains data
acquired by the Voyager-1 Planetary Radio Astronomy (PRA) instrument
during the Saturn encounter. Since the PRA instrument is able to
observe planetary phenomenon at much larger ranges than other fields
and particles experiments, thus the PRA data cover a variable and
longer encounter period. PRA lowband data provided here cover the
entire Saturn Encounter Phase (1981-06-05 to 1981-09-28).
VG1-S-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 corresponds, 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
space 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 [LEBLANCETAL1987].
Missing or bad data values are set to zero. If the status word
is zero, any data in that receiver sweep should be discarded.
CONFIDENCE_LEVEL_NOTE =
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.
Data Coverage
=============
Filename Records Start Stop
-----------------------------------------------------------------------
Volume ID: VG_1601
PRA.TAB 6228 1980-11-11T22:09:23.000Z 1980-11-16T23:59:47.000Z
Missing Data Flag
=================
Any data column whose value is 0 is missing data value.
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