PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 1998-05-01 NOTE = "DATASET.TXT contains the data set description." END_OBJECT = TEXT END Data Set Summary ================ Data Set ID: VG1-J-PWS-2-RDR-SA-4.0SEC-V1.1 Instrument: PWS Instrument P.I.: Donald A. Gurnett Data Supplier: William S. Kurth Data sampling rate: 4 seconds Data Set Start time: 1979-02-28T00:00:00.000Z Data Set Stop time: 1979-03-23T00:00:00.000Z Data column descriptions ------------------------ year integer_2 year past 1900 in units of years hours integer_2 hour of year starting at 24 in units of hours second integer_2 second of hour in units of seconds milli integer_2 millisecond of second in units of milliseconds fd_mod16 integer_2 FDS modulo 65536 (spacecraft clock) count fd_mod60 integer_2 FDS modulo 60 (spacecraft clock) count fd_lines integer_2 FDS line (spacecraft clock) count (1-800) inst_mod integer_2 instrument data format mode (0-31) channel integer_32 16 2-byte channels of uncalibrated e-field for channel n. Channels 01-16 have center frequencies ranging from 10 Hz to 56.2 kHz, logarithmically spaced in frequency, four channels per decade. For more information regarding data channel center frequencies and width, plus a description of how to convert these uncalibrated 'data numbers' to antenna voltages, refer to the 'Data Description section below. Record format ------------- The calibration table VG1PWSCL.TAB can be read according to the FORTRAN format statement: '(i3,16(1x,1pe8.2))' Data Description ================ Version 1.1 ----------- This version 1.1 data set replaces the version 1.0 data set (DATA_SET_ID = VG1-J-PWS-2-SA-4.0SEC) previously archived with the PDS. Changes to this version include the upgrade of the associated labels and templates to PDS version 3 compliance. Data Set Description -------------------- This data set consists of 4-second edited, wave electric field intensities from the Voyager 1 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 VG1PWSCL.TAB (for Voyager-1). 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 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 1 PWS: real*4 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, 7.07 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 each Voyager spacecraft are given below: VOYAGER 1 PWS SPECTRUM ANALYZER Voyager-1 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 10.06 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 Data Object Type : Time Series Processing Level ID : 4 Software Flag : Y Processing Start Time : 1988-02-01T Processing Stop Time : N/A Parameters ---------- Sampling Parameter Name : TIME Sampling Parameter Resolution : 4.0 Minimum Sampling Parameter : 1977-09-05T14:20 Maximum Sampling Parameter : N/A Sampling Parameter Interval : 4.0 Minimum Available Sampling Int : 4.0 Sampling Parameter Unit : SECOND Data Set Parameter Name : PLASMA WAVE SPECTRUM Noise Level : 5.E-6 Data Set Parameter Unit : V/m Processing ---------- Software Name : CDMAKE Source Data Set ID : VG1-J-PWS-2-SMS Product Data Set ID : VG1-J-PWS-2-SA-4.0SEC Node ID : F&P-IOWA Software Release Date : 1988-08-01T Software Type : FORTRAN Cognizant Full Name : MR. LARRY J. GRANROTH Software Accessibility Desc : NOT FOR PUBLIC USE CDMAKE is primarily a data format translation routine which is used to convert Voyager 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 CD production. Software -------- PWS16PC ------- PWS16PC is a PC version of the 'workhorse' display software used to survey and analyze in detail the Voyager plasma wave receiver's 16-channel spectrum analyzer data. It's basic function is to plot intensity as a function of time for all 16 of the channels whose center frequencies run from 10 Hz to 56.2 kHz. The default plot is a strip-chart like display where the average signal strength is plotted as a solid area above the baseline of each channel and peak measurements determined over the same intervals as the averages are plotted as a line over the averages. The software is designed to run directly from the CD for PC's with 800 x 600 16 color display capabilities. 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]. 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 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.