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VG2 J/S/U/N/SS PWS EDITED SPECTRUM ANALYZER FULL RES V1.0 (PDS)

NSSDCA ID: PSFP-00641

Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1977-08-20 to 

Description

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

Data Set Overview

This data set consists of electric field spectrum analyzer data from the Voyager 2 Plasma Wave Subsystem obtained during the entire mission. Data after 2007-08-31 will be added to the archive on subsequent volumes. The data set encompasses all spectrum analyzer observations obtained in the cruise mission phases before, between, and after the Jupiter and Saturn encounter phases as well as those obtained during the two encounter phases. The Voyager 2 spacecraft travels from Earth to beyond 80 AU over the course of this data set. To provide some guidance on when some key events occurred during the mission, the following table is provided. Date Event 1977-08-20 Launch 1979-07-02 First inbound bow shock crossing at Jupiter 1979-08-03 Last outbound bow shock crossing at Jupiter 1981-08-24 First inbound bow shock crossing at Saturn 1981-08-31 Last outbound bow shock crossing at Saturn 1982-04-26 10 AU 1983-08-30 Onset of first major LF heliospheric radio event 1986-01-24 First inbound bow shock crossing at Uranus 1986-01-29 Last outbound bow shock crossing at Uranus 1986-05-26 20 AU 1989-08-07 30 AU 1989-08-24 First inbound bow shock crossing at Neptune 1989-08-28 Last outbound bow shock crossing at Neptune 1992-07-06 Onset of second major LF heliospheric radio event 1993-05-08 40 AU 1996-10-10 50 AU 2000-01-27 60 AU 2002-11-01 Onset of third major LF heliospheric radio event 2003-04-21 70 AU 2006-07-01 80 AU 2009-09-03 90 AU 2012-11-04 100 AU Data Sampling ============= This data set consists of full resolution edited, wave electric field intensities from the Voyager 2 Plasma Wave Receiver spectrum analyzer obtained during the entire mission. For each time 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. The time between spectra in this data set vary by telemetry mode and range from 4 seconds to 96 seconds. During data gaps where complete 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. For the cruise data sets, the timing of samples is dependent upon the spacecraft telemetry mode. In principle, one can determine the temporal resolution between spectra simply by noting the difference in time between two records in the files. In some studies, more precise timing information is necessary. Here, we describe the timing of the samples for the PWS low rate data as a function of telemetry mode. The PWS instrument uses two logarithmic compressors as detectors for the 16-channel spectrum analyzer, one for the bottom (lower frequency) 8 channels, and one for the upper (higher frequency) 8 channels. For each bank of 8 channels, the compressor sequentially steps from the lowest frequency of the 8 to the highest in a regular time step to obtain a complete spectrum. At each time step, the higher frequency channel is sampled 1/8 s prior to the lower frequency channel so that the channels are sampled in the following order with channel 1 being the lowest frequency channel (10 Hz) and 16 being the highest (56.2 kHz): 9, 1, 10, 2, 11, 3, ... 15, 7, 16, 8. The primary difference between the various data modes is the stepping rate from one channel to the next (ranging from 0.5 to 12 s, corresponding to temporal resolutions between complete spectra of 4 s to 96 s). In the following table, we present the hexadecimal id for the various telemetry modes, the mode mnemonic ID, the time between frequency steps, and the time between complete spectra. We also provide the offset from the beginning of the instrument cycle (one complete spectrum) identified as the time of each record's time tag to the time of the sampling for the first high-frequency channel (channel 9) and for the first low-frequency channel (channel 1). Time Frequency Between High Freq. Low Freq. MODE (Hex) MODE ID Step (s) Spectra (s) offset (s) offset (s) 01 CR-2 0.5 4.0 0.425 0.4325 02 CR-3 1.2 9.6 1.125 1.1325 03 CR-4 4.8 38.4 0.425 0.4325 04 CR-5 9.6 76.8 0.425 0.4325 05 CR-6 12. 96.0 0.9275 0.935 06 CR-7 NOT IMPLEMENTED 07 CR-1 0.5 4.0 0.225 0.2325 08 GS-10A SAME AS GS-3 0A GS-3 0.5 4.0 0.425 0.4325 0C GS-7 SAME AS GS-3 0E GS-6 SAME AS GS-3 16 OC-2 SAME AS GS-3 17 OC-1 SAME AS GS-3 18 **CR-5A 0.5 4.0 0.425 0.4325 19 GS-10 SAME AS GS-3 1A GS-8 SAME AS GS-3 1D **UV-5A SAME AS CR-5A **In CR-5A and UV-5A, the PWS is cycled at its 0.5 sec/frequency step or 4 sec/spectrum rate, but 4 measurements are summed on board in 10-bit accumulators and these 10-bit sums are downlinked. On the ground, the sums are divided by 4, hence providing, in a sense, 16-second averages. One of every 12 sets of sums is dropped on board in order to avoid LECP stepper motor interference. Data Processing =============== The spectrum analyzer data are a continuous (where data are available) low resolution data set which provides wave intensity as a function of frequency (16 log-spaced channels) and time (one spectrum per time intervals ranging from 4 seconds to 96 seconds, depending on telemetry mode). The data are typically plotted as amplitude vs. time for one or more of the channels in a strip-chart like display, or can be displayed as a frequency-time spectrogram using a gray- or color-bar to indicate amplitude. With only sixteen channels, it is usually best to stretch the frequency axis by interpolating from one frequency channel to the next either linearly or with a spline fit. One must be aware if the frequency axis is stretched that more resolution may be implied than is really present. The Voyager PWS calibration table is given in an ASCII text file named VG2PWSCL.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 this file and a tutorial in its application. Descriptive headers have been removed from this 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 = 'VG2PWSCL.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 spacecraft 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 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: c 'the old noise level' for vg2 pws real tonl(9:16) /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 * float (idn(ichan))) else idn(ichan) = int (tonl(ichan) + 20.113 + & 0.99 * float (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. This correction is applicable to all data after 1977-12-21 21:53:36 UTC. It should not be applied to any data before 1977-09-24 00:47 UTC. For the cruise data sets, the timing of samples is dependent upon the spacecraft telemetry mode. In principle, one can determine the temporal resolution between spectra simply by noting the difference in time between two records in the files. In some studies, more precise timing information is necessary. Here, we describe the timing of the samples for the PWS low rate data as a function of telemetry mode. Additional information about this data set and the instrument which produced it can be found elsewhere in this catalog. A complete instrument description can be found in [SCARF&GURNETT1977]. Data ==== The spectrum analyzer data are a continuous (where data are available) low resolution data set which provides wave intensity as a function of frequency (16 log-spaced channels) and time (one spectrum per time intervals ranging from 4 seconds to 96 seconds, depending on telemetry mode). Each sample is nominally an 8-bit value which is roughly proportional to the log of the signal strength. In telemetry modes CR-5A and UV-5A the values are 10-bit sums of 4 original 8-bit instrument samples. Zero values indicate missing samples and negative values indicate samples flagged as contaminated by interference (see below). Ancillary Data ============== None Coordinates =========== The electric dipole antenna detects electric fields in a dipole pattern with peak sensitivity parallel to the spacecraft x-axis. However, no attempt has been made to correlate the measured field to any particular direction such as the local magnetic field or direction to a planet. This is because the spacecraft usually remains in a 3-axis stabilized orientation almost continuously. The only exception to this are a small number of occasions during calibration turns when the modulation of the low-frequency heliospheric radio emission could be used to do direction-finding on the source of these emissions [GURNETTETAL1998].

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

https://pds-ppi.igpp.ucla.edu/data/VG2-J-S-U-N-SS-PWS-2-RDR-SAFULL-V1.0/

Alternate Names

  • VG2-J/S/U/N/SS-PWS-2-RDR-SAFULL-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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