/*============================================================================*/ /* Streamlined Data Set Template (combined EB and SC data sets) */ /*============================================================================*/ /* Template: Data Set Template Rev: 1993-09-24 */ /* Note: Complete one for each data set. Identify multiple targets */ /* associated with the data set by repeating the 3 lines for the */ /* DATA_SET_TARGET object. Identify multiple hosts associated */ /* with the data set by repeating the 4 lines for the */ /* DATA_SET_HOST object. Identify multiple references associated */ /* with the data set by repeating the 3 lines of the */ /* DATA_SET_REFERENCE_INFORMATION object. */ /* Hierarchy: DATA_SET */ /* DATA_SET_INFORMATION */ /* DATA_SET_TARGET */ /* DATA_SET_HOST */ /* DATA_SET_REFERENCE_INFORMATION */ OBJECT = DATA_SET DATA_SET_ID = "VG1-SS-PWS-2-RDR-SA-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = " VG1 SOLAR WIND PWS EDITED RDR UNCALIB SPECTRUM ANALYZER V1.0" DATA_SET_COLLECTION_MEMBER_FLG = N START_TIME = 1977-09-05 STOP_TIME = UNKNOWN DATA_SET_RELEASE_DATE = 1995-01-16 PRODUCER_FULL_NAME = "DR. WILLIAM S. KURTH" DETAILED_CATALOG_FLAG = N DATA_SET_DESC = " This data set consists of edited, wave electric field intensities from the Voyager 1 Plasma Wave Receiver spectrum analyzer obtained during the cruise portions of the Voyager 1 mission, including data acquired during the various encounters. 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. 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. 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 zero.) 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 FORTRAN code may be used to load a calibration array for Voyager 1 PWS: real cal(16, 0:255) open ( unit=10, file='vg1pwscl.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, 7.07m. That is: efield = volts / 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 = efield ** 2 / bandwidth(ichan) Finally, power flux may be obtained by dividing the spectral density by the impedance of free space in ohms: pwrflux = specdens / 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 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 10.1 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 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 nmemonic 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. Additional information about this dataset and the instrument which produced it can be found elsewhere in this catalog. A complete instrument description can be found in Scarf and Gurnett [1977]." CONFIDENCE_LEVEL_NOTE = " This data set includes all available spectrum analyzer data within the interval of time covered. The data obtained within planetary magnetospheres 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. This periodic noise spike elimination has not, in general, been performed for the data taken outside of planetary magnetosphere (in the solar wind). 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." END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "SOLAR WIND" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = VG1 INSTRUMENT_ID = PWS END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "GURNETT&SCARF1977" END_OBJECT = DATA_SET_REFERENCE_INFORMATION END_OBJECT = DATA_SET