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. Future data will be added to this collection as they become available. The data set encompasses all spectrum analyzer observations obtained in the cruise mission phases before, between, and after the Jupiter, Saturn, Uranus, and Neptune encounter phases as well as those obtained during the encounter phases. The Plasma Wave Subsystem instrument is described in: Scarf, F. L., & Gurnett, D. A. (1977). A plasma wave investigation for the Voyager mission. Space Science Reviews, 21, 289-308. https://doi.org/10.1007/BF00211543 The Voyager 2 spacecraft travels from Earth to beyond 130 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 2007-08-31 Termination shock crossing 2009-09-03 90 AU 2012-11-04 100 AU 2016-01-01 110 AU 2018-11-05 119 AU Heliopause crossing 2019-03-01 120 AU 2022-04-06 130 AU 2025-06-21 140 AU 2028-08-15 150 AU Data Sampling ============= This data set consists of full resolution calibrated, wave electric field intensities in V/m 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. These data are produced onboard the spacecraft continuously and are meant to be telemetered directly to the ground (no store and playback), but the spacecraft is only tracked a variable number of hours per day, hence, particularly for cruise phases, there are typically only of order 8 hours of data per day. Data are calibrated. A summary of calibration procedures and tables used to produce this data set are provided for information; 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. Parent Data Set =============== These data are a fully calibrated version of the originally archived PDS3 data included in: VOYAGER PWS DATA: VG2-J/S/U/N/SS-PWS-2-RDR-SAFULL-V1.0 https://doi.org/10.17189/1519961 In addition to being fully calibrated, they have been reformatted into CDF format for ease in access. The remainder of this file describes the calibration procedure used to arrive at the values in the present data collection. 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 'instrument 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, CHAN_01, CHAN_02, CHAN_03, CHAN_04, CHAN_05, CHAN_06, ... CHAN_16. 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 mapping from insturment data numbers to voltages for each frequency channel. For example, the following C code may be used to load a calibration array for Voyager 2 PWS: int idn; double cal[256][16]; FILE* file = fopen(''VG2PWSCL.TAB'', ''rb''); for(int iamp = 0; iamp < 256; ++iamp){ fscanf(file, '' %3d'', idn); for(int ichan = 0; ichan < 16; ichan) fscanf(file, '',%8lE'', cal[iamp][ichan]); } ( Here two single quotes, '', are use in place of double-quote characters due to PDS documentation limitations. ) Then, given an instrument data value idn for the frequency channel with index, ichan, the corresponding calibrated antenna voltage would be given by the following array reference: volts[ichan] = cal[idn][ichan]; 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[ichan] = volts[ichan] / 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[ichan] = (efield * efield) / bandwidth[ichan]; 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 Finally, power flux may be obtained by dividing the spectral density by the impedance of free space in ohms: pwrflux[ichan] = specdens[ichan] / 376.73; Of course, for a particular application, it may be more efficient to apply the above conversions to the calibration table directly. Voyager 2 PWS SA Data Number Correction --------------------------------------- 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 C assumes that uncalibrated data numbers are stored in a 16-element integer array, named 'idn', with the array index equal to the PWS channel number minus one: float tonl[8] = {2.0, 1.0, -1.0, -2.0, -3.0, 1.0, 2.0, 1.0}; /* Instrument data number correction for upper 8 channels from: * * 1977-267T00:47 to 1977-283T16:00 * 1978-010T20:04 to 2006-324T20:50 */ for(int ichan = 8; ichan < 16; ++ichan){ if( idn[ichan] <= 0 ) continue; if( idn[ichan] < 64) idn[ichan] = 64; if( idn[ichan] <= 72 ) idn[ichan] = (int)(tonl[ichan-8] - 530.4 + 8.6*idn[ichan] ); else idn[ichan] = (int)(tonl[ichan-8] + 20.133 + 0.99*idn[ichan]); /* Telemetry bit errors can result in corrections above 255 */ if(idn[ichan] > 255) idn[ichan] = 255; } /* Instrument data number correction for upper 8 channels from: * * 1977-283T16:00 to 1977-312T20:12 * 1977-335T21:54 to 1978-010T20:04 * 2006-324T20:50 to present (at least 2016-245) */ for(int ichan = 8; ichan < 16; ++ichan){ if( idn[ichan] <= 0 ) continue; if( idn[ichan] < 64) idn[ichan] = 64; if( idn[ichan] <= 86 ) idn[ichan] = (int)(tonl[ichan-8] - 650.8 + 8.6*idn[ichan] ); else idn[ichan] = (int)(tonl[ichan-8] + 6.253 + 0.99*idn[ichan] ); /* Telemetry bit errors can result in corrections above 255 */ if(idn[ichan] > 255) idn[ichan] = 255; } These correction should not be applied permanently to the Voyager 2 calibration table since they are valid for a limited time span and may be modified in the future. These corrections are applicable to data in the UTC time ranges noted in the source comments above and should be applied as if all data values are 8-bit measurements. For 10-bit sums (modes CR-5A and UV-5A, i.e. TELETMETRY_MODE column values 0x18 and 0x1D) data numbers must first be divided by 4, and then corrected with the algorithms above. 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). Note that none of these data are recorded onboard and are simply streamed to the telemetry downlink in realtime. Hence, data only exist if there is a link to a Deep Space Network (DSN) complex established. Coverage was nearly complete for the planetary flybys but are limited by DSN coverage for the Voyager Interstellar Mission (VIM). Typical coverage for VIM is 8 hours per day, but can be as short as two or three hours and can be as much as 16 hours or more. Occasionally, no coverage is available due to DSN contention or other circumstances, in which case some days may have no data in which case no file is created. 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]." CONFIDENCE_LEVEL_NOTE = " Overview ======== This data set includes all available spectrum analyzer data acquired during the Voyager 2 mission to date. 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 random intense spikes of noise below 1 kiloHertz due to the operation of attitude control thrusters. 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, see discussion in the "Data" section describing the fact that data only exist when the spacecraft downlinks to the DSN in realtime, which is usually much less than a full day. A failure in the Voyager 2 flight data system on September 24, 1977 has decreased the sensitivity and the calibration accuracy of the upper 8 spectrum analyzer channels (i.e. 1 kiloHertz and higher). One aspect of this failure is that voltages on other inputs to a multiplexer shared by the PWS upper 8 channels can affect the PWS data. Hence, if all 8 upper channels move up and down together, it is likely this is a side effect of the failure and not a real effect in the PWS data. An intermittent failure appeared in the Voyager 2 17.8 Hz channel beginning on November 6, 1995. The channel now exhibits three states. In the original failed state, the channel becomes very noisy, outputting an abnormally large signal. In a second failed state, the output goes to zero. However, for the majority of the time since the failure, the channel outputs credible measurements in the correct amplitude range. Beginning in May 2001 the Voyager 2 wideband receiver began to display degraded operation and by September of 2002, the receiver showed virtually no response. Attempts to playback wideband data from Voyager 2 have ceased. Review ====== This archival data set was examined by a peer review panel prior to its acceptance by the Planetary Data System (PDS). The peer review was conducted in accordance with PDS procedures. Prior to creation of the final version of the archival data set, key elements of the archive were distributed for preliminary review. These included electronic versions of example PDS labels, CATALOG files, and Software Interface Specifications. These materials were distributed to PDS personnel, the experiment investigator, and others, as appropriate.