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VG2 NEP PWS EDITED RDR UNCALIB SPECTRUM ANALYZER 4SEC V1.0 (PDS)

NSSDCA ID: PSFP-00592

Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1989-08-21 to 1989-08-31

Description

This description was generated automatically using input from the Planetary Data System.

Data Set Overview ================= This data set consists of 4-second edited, wave electric field intensities from the Voyager 2 Plasma Wave Receiver (PWS) spectrum analyzer obtained in the vicinity of the Neptunian 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. Parameters ========== Derived Parameters -----------------Sampling Parameter Name : TIME Sampling Parameter Resolution : 4.0 seconds Minimum Sampling Parameter : N/A Maximum Sampling Parameter : N/A Sampling Parameter Interval : 4.0 seconds Minimum Available Sampling Interval : 4.0 seconds Data Set Parameter Name : plasma wave spectrum Noise Level : 0.000005 V/m Data Set Parameter Unit : volts/meter Plasma wave spectrum: 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. Measured Parameters ------------------Electric field component: A measured parameter equaling the electric field strength (e.g. in milli-volts per meter) along a particular axis direction. Wave magnetic field intensity: A measured parameter equaling the magnetic field strength in a specific frequency passband (in MKS unit: volts/meter) measured in a single sensor or antenna. Wave electric field intensity: A measured parameter equaling the electric field strength in a specific frequency passband (in MKS unit: volts/meter) measured in a single sensor or antenna. Processing ========== The data files in this data set were created using the 'CDMAKE' software. CDMAKE -----Node ID : PPI-IOWA Software Release Date : 1988-08-01 Cognizant Full Name : MR. LARRY J. GRANROTH 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. 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. These calibration files are always provided with the dataset when the data are extracted from PDS by a user. 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 2 PWS: ' real*4 cal (16,0:255) ' ' open ( unit=10, file='vg2pwscl.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))' ' / (120. * pi)' 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, Uranus, and Neptune 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 PASCAL function roughly corrects the upper 8 channels of the Voyager 2 PWS spectrum analyzer instrument after the Flight Data System failure which occurred during Earth-Jupiter cruise. Input is a raw integer data number and the PWS channel number in which it occurred. Output is the corrected integer data number. ---------------------------- -------------------------------- } { Define a table of constants to be indexed by Voyager 2 PWS channel numbers in the range 9 through 16, inclusive. (These are the only channels affected by this correction algorithm.) } CONST oldNoiseLevel : ARRAY [9..16] OF REAL = (2.0, 1.0, -1.0, -2.0, -3.0, 1.0, 2.0, 1.0); BEGIN { function correct V2PwsUpper8Channels } { Correct only Voyager 2 PWS upper 8 channels. } IF (channel >= 9) AND (channel <= 16) THEN BEGIN { Non-positive data numbers represent missing or invalid data. } IF dataNumber > 0 THEN BEGIN { Set positive data numbers less than 64 to 64. } IF dataNumber < 64 THEN dataNumber := 64; { If the data number is less than or equal to 74 then set the data number to the integer truncation of the result of the sum of the table value indexed by the channel number, minus 530.4, plus 8.6 times the dataNumber. } IF dataNumber <= 72 THEN dataNumber := TRUNC ( oldNoiseLevel[channel] - 530.4 + 8.6 * dataNumber ) { Otherwise, if the data number is greater than 74 then set the data number to the integer truncation of the result of the sum of the table value indexed by the channel number, plus 20.113, plus 0.99 times the dataNumber. } ELSE dataNumber := TRUNC ( oldNoiseLevel[channel] + 20.113 + 0.99 * dataNumber ); END END; correctV2PwsUpper8Channels := dataNumber; END; { function correctV2PwsUpper8Channels } BEGIN END. 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 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. [1989] and a complete instrument description can be found in Scarf and Gurnett [1977].

These data are available on-line from the Planetary Data System (PDS) at:

https://pds-ppi.igpp.ucla.edu/data/VG2-N-PWS-2-RDR-SA-4SEC-V1.0/

Alternate Names

  • VG2-N-PWS-2-RDR-SA-4SEC-V1.0

Discipline

  • Planetary Science: Fields and Particles

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II

 

Personnel

NameRoleOriginal AffiliationE-mail
Prof. Donald A. GurnettData ProviderUniversity of Iowa
Dr. William S. KurthGeneral ContactUniversity of Iowawsk@space.physics.uiowa.edu
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