Data Set Overview : Data Set Description -------------------- This data set consists of 4-second edited, wave electric field intensities from the Voyager 2 Plasma Wave Receiver spectrum analyzer obtained in the vicinity of the Jovian 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 table is given in an ASCII text file named SA_CL.TAB (for Voyager-2). This provides 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. Descriptive headers have been removed from the calibration table file. The columns included are IDN, ICHAN01, ICHAN02, ICHAN03, ICHAN04, ICHAN05, ICHAN06, ... ICHAN16. 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 2 PWS: real*4 cal (16,0:255) open ( unit:10, file:'SA_CL.TAB', status:'old' ) 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, 7.07 m. 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 2 PWS are given below: VOYAGER 2 PWS SPECTRUM ANALYZER Voyager-2 Channel Center Frequency Bandwidth 1 10.0 Hz 2.16 Hz 2 17.8 Hz 3.58 Hz 3 31.1 Hz 4.50 Hz 4 56.2 Hz 10.7 Hz 5 100. Hz 13.8 Hz 6 178. Hz 28.8 Hz 7 311. Hz 39.8 Hz 8 562. Hz 75.9 Hz 9 1.00 kHz 75.9 Hz 10 1.78 kHz 151. Hz 11 3.11 kHz 324. Hz 12 5.62 kHz 513. Hz 13 10.0 kHz 832. Hz 14 17.8 kHz 1260. Hz 15 31.1 kHz 2400. Hz 16 56.2 kHz 3800. Hz A failure in the Voyager 2 Flight Data System which occurred about 3 months after launch has adversely affected the calibration of PWS channels 9 through 16. An algorithm has been devised to partially correct for this failure, and has proven useful for Voyager 2 Jupiter, Saturn, and Uranus encounters, but is not valid for Earth-Jupiter cruise and may be modified in the future. The following implementation of this correction algorithm in VAX FORTRAN assumes that uncalibrated data numbers are stored in a 16-element integer array, idn, with the array index equal to the PWS channel number: real*4 tonl(9:16) ! the old noise level for v2 data tonl/2.0,1.0,-1.0,-2.0,-3.0,1.0,2.0,1.0/ do ichan:9,16 if (idn(ichan).gt.0) then if(idn(ichan).lt.64) idn(ichan):64 if (idn(ichan).le.72) then idn(ichan):int(tonl(ichan)-530.4+8.6*real(idn(ichan))) else idn(ichan):int(tonl(ichan)+20.113+0.99*real(idn(ichan))) end if end if end do This correction should not be applied permanently to the Voyager 2 calibration table since it is valid for a limited time span and may be modified in the future. Additional information about this data set 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 [SCARFETAL1979] and a complete instrument description can be found in [SCARF&GURNETT1977]. Processing Level ID : 2 Software Flag : Y Processing Start Time : 1988-02-01 Parameters : Sampling Parameter Name : TIME Data Set Parameter Name : PLASMA WAVE SPECTRUM Sampling Parameter Resolution : 4.000000 Minimum Sampling Parameter : 197708201553.000000 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 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 : VG2 Data Set Parameter Name : PLASMA WAVE SPECTRUM Instrument Parameter Name : ELECTRIC FIELD WAVEFORM Instrument Parameter Name : ELECTRIC FIELD COMPONENT Instrument Parameter Name : MAGNETIC FIELD COMPONENT Instrument Parameter Name : WAVE ELECTRIC FIELD INTENSITY Instrument Parameter Name : WAVE MAGNETIC FIELD INTENSITY Important Instrument Parameters : 1 (for all parameters)

Confidence Level Overview : This data set includes all available spectrum analyzer data within the interval of time covered. The data set has been cleaned as well as possible for periodic noise spikes due to a stepper motor operating on the LECP and a modulated grid within the PLS. The 'bad' points remain in the data set as negative numbers with the same absolute value as the original data point so that the point can be skipped in normal data processing by testing for negative values or recovered for special inspection by converting the sign back to a positive one. Other possible sources of noise which have not been eliminated include a nearly continuous tone at about 311 Hz after closest approach due to interference from the gyros and random intense spikes of noise below 1 kiloHertz due to the operation of attitude control thrusters. The data between 0040 and 0155 spacecraft event time on July 10 1979 is heavily contaminated by thruster activity associated with a trajectory correction maneuver. Other randomly occurring spikes or time periods of intense spikes over the entire frequency range are indicative of telemetry errors. No attempt has been made to remove spikes since some could be valid data, i.e. real bursts of wave activity. The 17.8-Hz channel is sometimes contaminated by interference from the PRA instrument, depending on that instrument's mode. This interference is at a relatively constant level. Also, a failure in the Voyager 2 flight data system a few months after launch has decreased the sensitivity and the calibration accuracy of the upper 8 spectrum analyzer channels (i.e. 1 kiloHertz and higher). Data Coverage and Quality : Filename Records Start Stop ---------------------------------------------------------------------- Volume ID: VG_1601 SA_4S.DAT 170560 1981-08-24T00:00:47.537Z 1981-08-31T23:56:46.846Z SA_CL.TAB 356