Data Set Overview
  =================
    This data set consists of electric field waveform samples from the
    Voyager 2 Plasma Wave Receiver waveform receiver obtained during
    the Neptune encounter. The waveforms are collections of 4-bit
    samples of the electric field measured by the dipole electric antenna
    at a rate of 28,800 samples per second.  1600 samples are collected
    in 55.56 msec followed by a 4.44-msec gap. Each 60-msec interval
    constitutes a line of waveform samples. The data set includes about 271
    frames of waveform samples consisting of up to 800 lines, each.  The
    telemetry format for the waveform data is identical to that for
    images, hence the use of line and frame as constructs in describing
    the form of the data.  The waveform is sampled through a bandpass
    filter with a passband of 40 Hz to 12 kHz.  The 4-bit samples
    provide sixteen digital values of the electric field with a
    linear amplitude scale, but the amplitude scale is arbitrary
    because of the automatic gain control used in the waveform
    receiver.  The instantaneous dynamic range afforded by the 4
    bit samples is about 23 db, but the automatic gain control allows
    the dominant signal in the passband to be set at the optimum
    level to fit within the instantaneous dynamic range.  With the gain
    control, the overall dynamic range of the waveform receiver
    is about 100 db.  The automatic gain control gain setting is not
    returned to the ground, hence, there is no absolute calibration
    for the data.  However, by comparing the waveform spectrum derived
    by Fourier transforming the waveform to the spectrum provided by
    the spectrum analyzer data, an absolute calibration may be
    obtained in most cases.  The data may be plotted in raw form to
    show the actual waveform; this is useful for studying events such
    as dust impacts on the spacecraft.  But the normal method of
    analyzing the waveform data is by Fourier transforming the samples
    from each line to arrive at an amplitude versus frequency spectrum.
    By stacking the spectra side-by-side in time order, a frequency-
    time spectrogram can be produced.

    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].


  Parameters
  ==========

    Derived Parameters
    ------------------

      Sampling Parameter Name             : time
      Sampling Parameter Resolution       : 0.000034722 seconds
      Minimum Sampling Parameter          : n/a
      Maximum Sampling Parameter          : n/a
      Sampling Parameter Interval         : 0.000034722 seconds
      Minimum Available Sampling Interval : 0.000034722 seconds
      Data Set Parameter Name             : plasma wave waveform
      Noise Level                         : 0.000005
      Data Set Parameter Unit             : volt/meter (Data not
                                                        absolutely
                                                        calibrated)

      Plasma wave waveform: A plasma wave waveform is a time series of
      measurements of the electric or magnetic field component of the
      wave spectrum taken through a broadband filter.  The temporal
      sample rate is normally such that samples are made at more than
      twice the analysis filter bandwidth.  A typical waveform will
      consist of the order of 1000 contiguous samples of between 4 and
      12 bits each.  For a 10-kHz analysis bandwidth, the sample rate
      would normally be approximately 25 kHz or 25,000 samples/second.
      Once received, the waveforms are typically Fourier transformed in
      order to provide an amplitude versus frequency spectrum across
      the analysis bandwidth.  The sample rate, then, is required to be
      at least a factor of two greater than the filter bandwidth in
      order to avoid aliasing in the transformed spectrum.  The spectra
      can be stacked side-by-side in time to build a frequency-time
      spectrogram (that is, amplitude as a function of time and
      frequency) in order to identify the temporal and spectral
      variations in the wave spectrum.  Alternately, the untransformed
      time series can be used to study the details of the waveform.
      This has been useful for measuring small-scale structures in the
      plasma and for identifying the signature of micron-sized dust
      impact on the spacecraft.


    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 'CDREF'
    software.

    CDREF
    -----
      Node ID                             : IMAGING
      Software Release Date               : 1990-04-07
      Cognizant Full Name                 : MR. JASON J. HYON

      CDREF is primarily a data format translation routine which is used
      to convert Voyager PWS EDR tape files to CD-ROM files.  CDREF is
      written in FORTRAN and is not available for public use. The EDR,
      or Engineering Data Records, are produced at Multi-mission Image
      Processing Laboratory at JPL as the uncalibrated, full-resolution
      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.

Confidence Level Overview
  =========================
    This data set includes all available waveform receiver data obtained
    during the Neptune encounter.  There has been no attempt
    to clean various interference signals from the data.  Most of these
    can normally be easily seen in frequency-time spectrograms as
    narrowband, fixed-frequency tones.  The most common include narrow-
    band tones at 2.4 and 4.8 kHz which are power supply harmonics.
    There is sometimes a tone near 1.7 kHz which is associated with
    the operation of the spacecraft gyros.  The spacecraft tape
    recorder results in a rather intense band in the frequency range
    of a few hundred Hz.  There are few times when the data in this
    frequency range can be used.  However, there are times when the
    real signals in this frequency range can exceed the intensity of
    the interference sufficiently so that the frequency range near
    a few hundred Hz can be used.  Use of the spectrum analyzer data
    can be of use to determine when these time periods occur.  The
    stepper motor of the LECP instrument also interferes in the
    frequency range of a few hundred Hz, but for periods of a few
    seconds.

    The LECP interference is very intense and captures the automatic
    gain control so that real signals, even where there is no
    interference, will appear to decrease in amplitude until the LECP
    interference fades in amplitude.  The PLS instrument periodically
    interferes at 400 Hz and odd harmonics because of a 400-Hz square
    wave used to modulate a grid in the detector.  The PLS interference
    lasts for several seconds and ends abruptly.  Telemetry errors
    result in a fairly graceful degradation of the waveform data.
    Assuming the telemetry errors are randomly occurring bursts, they
    typically appear as an enhanced background level in the spectrum.
    Since the bursts are short, their Fourier transform is a broadband
    spectrum. When looking for relatively narrowband features or
    features with distinct frequency-time characteristics, the result
    of the bursts simply reduce the signal-to-noise in the spectrum.
    One way of reducing the effect of burst telemetry errors is to pass
    the waveform data through a low-pass filter to despike it, prior to
    running the Fourier transform.  The waveform data is not subject
    to the negative effects of the failure in the Voyager 2 Flight
    Data System which reduces the sensitivity of the spectrum analyzer
    and affects the calibration above 1 kHz.  In fact, use of the 1 -
    12 kHz waveform data is an effective way of avoiding the problems
    with the spectrum analyzer data in this frequency range.


  Data Quality and Coverage
  =========================

    --------------------------------------------------------------------
    Table 1. Data Quality ID Descriptions
    --------------------------------------------------------------------
    ID   Description
    --------------------------------------------------------------------
    -1   no attempt has been made to specify a data quality for this
         time range
     1   Contamination removed by deleting measurements which are
         affected. Some contamination may still be present to avoid
         deleting too many data points. Remaining LECP contamination
         will appear as periodic bursts of noise in one or more
         channels in the range 100 Hertz to about 1 kiloHertz.


    --------------------------------------------------------------------
    Table 2. Data Contamination ID Descriptions
    --------------------------------------------------------------------
    ID   Description
    --------------------------------------------------------------------
    -1   no evaluation of possible contamination has been made
     1   Contamination code 01 refers to contamination by the LECP
         stepper motor and PLS grid modulation which causes periodic
         spikes in the spectrum analyzer data particularly in the
         frequency range 100 Hertz to about 1 kiloHertz.