DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set consists of 4-second edited, wave electric field
intensities from the Voyager 1 Plasma Wave Receiver spectrum
analyzer obtained in the vicinity of the Saturnian
magnetosphere. For each 4-second interval, a field strength is
determined for each of the 16 spectrum analyzer channels whose
center frequencies range from 10 Hertz to 56.2 kiloHertz and
which are logarithmically spaced in frequency, four channels
per decade. The time associated with each set of intensities
(16 channels) is the time of the beginning of the scan. During
data gaps where complete 4-second spectra are missing, no
entries exist in the file, that is, the gaps are not
zero-filled or tagged in any other way. When one or more
channels are missing within a scan, the missing measurements
are zero-filled. Data are edited but not calibrated. The data
numbers in this data set can be plotted in raw form for event
searches and simple trend analysis since they are roughly
proportional to the log of the electric field strength.
Calibration procedures and tables are provided for use with
this data set; the use of these is described below.
Use of Voyager PWS Calibration Tables
The Voyager PWS calibration tables are given in two plain ASCII
text files named VG1PWSCL.TAB and VG2PWSCL.TAB (for Voyagers-1
and -2, respectively). These provide information to convert
the uncalibrated `data number' output of the PWS 16-channel
spectrum analyzer to calibrated antenna voltages for each
frequency channel. Following is a brief description of these
files and a tutorial in their application.
The first column lists an uncalibrated data number followed by
the corresponding value in calibrated volts for each of the 16
frequency channels of the PWS spectrum analyzer. Each line
contains calibrations for successive data number values ranging
from 0 through 255. (Data number 0 actually represents the
lack of data since the baseline noise values for each channel
are all above that.)
A data analysis program may load the appropriate table into a
data structure and thus provide a simple look-up scheme to
obtain the appropriate voltage for a given data number and
frequency channel. For example, the following VAX FORTRAN code
may be used to load a calibration array for Voyager 1 PWS:
real*4 cal (16,0:255) open ( unit=10, file='vg1pwscl.tab',
status='old' ) do i=0,38 read (10,*) ! skip 38 lines of label
info end do do i=0,255 read (10,*) idn,
(cal(ichan,i),ichan=1,16) end do close (10)
Then, given an uncalibrated data value idn for the frequency
channel ichan, the corresponding calibrated antenna voltage
would be given by the following array reference:
volts = cal (ichan, idn)
This may be converted to a wave electric field amplitude by
dividing by the effective antenna length in meters, 7.07m.
That is:
efield = cal(ichan, idn) / 7.07
Spectral density units may be obtained by dividing the square
of the electric field value by the nominal frequency bandwidth
of the corresponding spectrum analyzer channel.
specdens = (cal(ichan,idn)/7.07)**2 / bandwidth(ichan)
Finally, power flux may be obtained by dividing the spectral
density by the impedance of free space in ohms:
pwrflux = ((cal(ichan,idn)/7.07)**2/bandwidth(ichan)) / 376.73
Of course, for a particular application, it may be more
efficient to apply the above conversions to the calibration
table directly.
The center frequencies and bandwidths of each PWS spectrum
analyzer channel for the Voyager 1 PWS are given below:
VOYAGER 1 PWS SPECTRUM ANALYZER
Voyager-1 Channel Center Frequency Bandwidth
1 10.0 Hz 2.99 Hz 2 17.8 Hz 3.77 Hz 3 31.1 Hz 7.50 Hz 4 56.2 Hz
10.06 Hz 5 100. Hz 13.3 Hz 6 178. Hz 29.8 Hz 7 311. Hz 59.5
Hz 8 562. Hz 106. Hz 9 1.00 kHz 133. Hz 10 1.78 kHz 211. Hz
11 3.11 kHz 298. Hz 12 5.62 kHz 421. Hz 13 10.0 kHz 943. Hz
14 17.8 kHz 2110. Hz 15 31.1 kHz 4210. Hz 16 56.2 kHz 5950.
Hz
Additional information about this dataset and the instrument
which produced it can be found elsewhere in this catalog. An
overview of the data in this data set can be found in Gurnett
et al. [1981] and a complete instrument description can be
found in Scarf and Gurnett [1977].
Processing Level Id : 2
Software Flag : Y
Processing Start Time : 1988-08-04
Parameters
==========
Sampling Parameter Name : TIME
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Sampling Parameter Resolution : 4.000000
Minimum Sampling Parameter : 197709051420.000000
Sampling Parameter Interval : 4.000000
Minimum Available Sampling Int : 4.000000
Data Set Parameter Unit : VOLT/METER
Noise Level : 0.000005
Sampling Parameter Unit : SECOND
Description
-----------
A set of derived parameters consisting of wave electric field
intensities or electric field spectral densities at various
contiguous frequencies over a range of frequencies. The MKS
units are: Volts/Meter or Volts**2/(Hertz.Meter**2),
respectively.
Source Instrument Parameters
============================
Instrument Host ID : VG1
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Instrument Parameter Name : ELECTRIC FIELD WAVEFORM
Important Instrument Parameters : 1
Instrument Host ID : VG1
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Instrument Parameter Name : ELECTRIC FIELD COMPONENT
Important Instrument Parameters : 1
Instrument Host ID : VG1
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Instrument Parameter Name : MAGNETIC FIELD COMPONENT
Important Instrument Parameters : 1
Instrument Host ID : VG1
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Instrument Parameter Name : WAVE ELECTRIC FIELD INTENSITY
Important Instrument Parameters : 1
Instrument Host ID : VG1
Data Set Parameter Name : PLASMA WAVE SPECTRUM
Instrument Parameter Name : WAVE MAGNETIC FIELD INTENSITY
Important Instrument Parameters : 1
Processing
==========
Processing History
------------------
Source Data Set ID : N/A
Software : UNK
Product Data Set ID : VG1-S-PWS-2-SA-4.0SEC
Source Data Set ID : VG1-S-PWS-2-SMSF
Software : CDMAKE
Product Data Set ID : VG1-S-PWS-2-SA-4.0SEC
Software 'CDMAKE'
-----------------
CDMAKE is primarily a data format translation routine which
is used to convert Voyager Plasma Wave Spectrometer (PWS)
MSF tape files to CD files. The MSF, or Master Science
Files, are produced at the University of Iowa as the
primary, ordered, full-information PWS spectrum analyzer
data set. The CD files contain uncalibrated, full-resolution
PWS data with minimal ancillary data in a simplified format
which may be used in CDROM production.
Note: SOFTWARE IS NOT AVAILABLE FOR PUBLIC USE.
Software Name : CDMAKE
Software Type : N/A
Software Release Date : 1988-08-01
Node ID : PPI-IOWA
Cognizant Engineer : MR. LARRY J. GRANROTH
Software Access Description : N/A
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