Data Set Overview
  =================
    The electron spectra are fit using several isotropic Maxwellian
    distribution functions to find electron parameters.  The spacecraft
    charge may seriously affect the density measurements. The temperature
    of each component is, however, independent of the spacecraft potential.
    To obtain the best estimate of the electron density, the encounter
    period is divided into four regions and four different analysis methods
    are used.


  Parameters
  ==========

    Derived Parameters
    ------------------
      Sampling Parameter Name             : time
      Sampling Parameter Resolution       : n/a
      Minimum Sampling Parameter          : unk
      Maximum Sampling Parameter          : unk
      Sampling Parameter Interval         : unk
      Minimum Available Sampling Interval : unk
      Data Set Parameter Name             : electron density
      Noise Level                         : unk
      Data Set Parameter Unit             : cm**-3

      Electron density: A derived parameter equaling the number of
      electrons per unit volume over a specified range of electron
      energy. Different forms of electron density are derived
      distinguished by method of derivation (Maxwellian fit, method of
      moments) or by the some selection criteria (i.e., hot electron
      and cold electron density). In general, if more than one electron
      component is analyzed, either by moment or fit, a total density
      will be provided which is the sum of the electron densities. If
      the electron do not have a Maxwellian distribution the actual
      distribution can be represented as the sum of several Maxwellians,
      in which case the density of each Maxwellian is given.

      Sampling Parameter Name             : time
      Sampling Parameter Resolution       : n/a
      Minimum Sampling Parameter          : unk
      Maximum Sampling Parameter          : unk
      Sampling Parameter Interval         : unk
      Minimum Available Sampling Interval : unk
      Data Set Parameter Name             : electron temperature
      Noise Level                         : unk
      Data Set Parameter Unit             : eV

      Electron temperature: A derived parameter giving an indication of
      the mean energy/electron, assuming the shape of the electron
      energy spectrum to be Maxwellian (i.e. highest entropy shape).
      Given that the electron energy spectrum is not exactly Maxwellian,
      the electron temperature can be defined integrally (whereby the
      mean energy obtained by integrating under the actual electron
      energy spectrum is set equal to the integral under a Maxwellian,
      where the temperature is a free parameter for which to solve), or
      differentially (whereby the slopes of the actually electron energy
      spectrum at various energies are matched to the slopes of a
      corresponding Maxwellian). The temperature parameter is often
      qualified with a range of applicable energies. Temperatures can be
      angularly anisotropic. If the electrons do not have a Maxwellian
      distribution the actual distribution can be represented as the sum
      of several Maxwellians, each with a separate temperature.


    Derived Parameters
    ------------------
      Electron Rate: A measured parameter equaling the number of
      electrons hitting a particle detector per specified accumulation
      interval. The counted electrons may or may not be discriminated as
      to their energies (e.g. greater than E1, or between E1 and E2).

      Electron Current: A measured parameter equaling the rate at which
      negative charge is collected by a particle detector. The electrons
      contributing to this current may be restricted by energy.
      Electrons always have a charge of 1, so this quantity corresponds
      directly to the electron rate.


  References
  ==========

    Zhang, M., J. D. Richardson, and E. C. Sittler, Jr.,
    Voyager 2 electron observations in the Magnetosphere
    of Neptune, J. Geophys. Res., in press, 1991.

    J. W. Belcher, H. S. Bridge, et al., Plasma
    Observations Near Neptune: Initial Results from
    Voyager 2, Science, 246, 1478-1483, 1989.

    Scudder, J. D., E. C. Sittler, Jr. and H. S. Bridge,
    A survey of the plasma electron environment of Jupiter:
    a view from Voyager,
    J. Geophys. Res., 86, 8319-8342, 1981.

    Sittler, E. C., Jr., K. W. Ogilvie and R. S. Selesnick,
    Survey of electrons in the Uranian magnetosphere: Voyager 2
    observations, J. Geophys. Res., 92, 15,263-15,281, 1987.

Confidence Level Overview
  =========================
    The electron parameters are reliable except near closest approach
    where the electrons are cold. In the time period between 237.03180
    and 237.11253, the cold component is below the threshold the PLS
    measurement.  A temperature of 3 eV is assumed for the cold
    component.  The spacecraft potential is not determined and is set
    equal to zero.  The parameters of the hot electron components are
    obtained directly from the fits and are reliable.  The cold
    electron density is set equal to the total ion density minus the
    hot electron density.  In this region the results have large
    error bars.

  Data Quality and Coverage
  =========================
    In the time period from 1989-08-24T14:38:04.130 (236.60977) to
    1989-08-24T19:45:17.571 (236.82312), when the spacecraft is in the
    inbound magnetosheath and is probably positively charged, a
    program written by Sittler (1987) is used to derive the electron
    density and temperature.
    The spacecraft potential is calculated by using Scudder's (1981)
    return current-spacecraft potential relation.  Estimates of the
    formal errors are not performed in Sittler's program.  Since the
    electrons are hot in this region, we are confident of the results.

    In the time periods from
    1989-08-24T22:46:35.334 (236.94902) to
    1989-08-24T23:32:12.481 (236.98070)
    and from
    1989-08-25T08:09:47.233 (237.34013) to
    1989-08-25T09:23:24.001 (237.39125),
    when the spacecraft is in hot plasma regions, all the electron
    parameters are derived from fits to the electron spectra.  Again,
    we are confident of the results.

    In the regions where a cold electron component is present in the
    spectra
    (1989-08-24T23:35:23.424 (236.98291) to
    1989-08-25T00:35:23.712 (237.02458)
    and from
    1989-08-25T04:33:48.095 (237.19014) to
    1989-08-25T08:02:35.233 (237.33513), the
    spacecraft is negatively charged and the density calculation is
    seriously affected by spacecraft charging.  The total ion density
    from the PLS ion measurements and the condition of charge
    neutrality are used to estimate the spacecraft potential.  The true
    density of each electron component is equal to d0*exp(-Vsc/T),
    where d0 is the density from the fits assuming a zero spacecraft
    potential, Vsc is the spacecraft potential and T is the temperature
    of that component.  Uncertainties in the electron density should
    thus mainly determined by the ion density calculation.  However,
    electron temperature calculations are not affected by the
    spacecraft charging, so they are quite accurate.

    In the time period from
    1989-08-25T00:45:47.520 (237.03180) to
    1989-08-25T02:42:02.592 (237.11253),
    the cold component is below the threshold the PLS measurement. A
    temperature of 3 eV is assumed for the cold component. The
    spacecraft potential is not available, so is set equal to zero.
    The parameters of the hot electron components are obtained directly
    from the fits.  The cold electron density is then set equal to the
    total ion density minus the hot electron density.  In this region
    the results have large error bars.

    In the region near closest approach
    (1989-08-25T04:11:23.712 (237.17458) to
     1989-08-25T04:25:34.752 (237.18443),
    where the loss-cone effect is prominent,  the density of each
    component is equal to d0*ditot/detot, where d0 is the density of
    the component calculated from the fits, ditot is the total ion
    density, detot is the total electron density from the fits.

    Table 1 contains hourly summaries of the percentage of the data
    available, data quality, and contamination codes. Tables 2 and 3
    contain descriptions of the data quality and data contamination
    ID's respectively.

    -------------------------------------------------------------------
    Table 1. Hourly Data Coverage and Quality Summaries
    -------------------------------------------------------------------
    Start Time           Mode            Percent  Qual  Contam  NumGood
    -------------------------------------------------------------------
    1989-08-24T15:00:54  E1/E2            35.135   -1     -1       182
    1989-08-24T16:00:29  E1/E2           129.730   -1     -1       672
    1989-08-24T17:09:40  E1/E2            81.081   -1     -1       420
    1989-08-24T18:00:29  E1/E2            72.973   -1     -1       378
    1989-08-24T19:00:29  E1/E2            94.595   -1     -1       490
    1989-08-24T22:46:35  E1/E2            37.838   -1     -1       196
    1989-08-24T23:01:00  E1/E2            16.216   -1     -1        84
    1989-08-25T00:00:59  E1/E2            81.081   -1     -1       420
    1989-08-25T01:09:48  E1/E2            51.351   -1     -1       266
    1989-08-25T02:06:03  E1/E2            43.243   -1     -1       224
    1989-08-25T04:11:23  E1/E2            21.622   -1     -1       112
    1989-08-25T05:01:00  E1/E2            56.757   -1     -1       294
    1989-08-25T06:00:59  E1/E2            78.378   -1     -1       406
    1989-08-25T07:00:59  E1/E2            45.946   -1     -1       238
    1989-08-25T08:01:00  E1/E2            54.054   -1     -1       280
    1989-08-25T09:00:59  E1/E2            51.351   -1     -1       266
    1989-08-25T09:23:24  E1/E2            16.216   -1     -1        84


    --------------------------------------------------------------------
    Table 2. Data Quality ID Descriptions
    --------------------------------------------------------------------
    ID   Description
    --------------------------------------------------------------------
    -1   no attempt has been made to specify a data quality for this
         time range

    --------------------------------------------------------------------
    Table 3. Data Contamination ID Descriptions
    --------------------------------------------------------------------
    ID   Description
    --------------------------------------------------------------------
    -1   no evaluation of possible contamination has been made