Description of the PDS LECP Neptune Scan data.

     This data consists of resampled data from the Low Energy
Charged Particle (LECP) Experiment on the Voyager 2 Spacecraft
for the period when Voyager 2 was in the vicinity of the planet
Neptune.  The period covered is 1989-08-24T00:00:00.000 SCET  to
1989-08-27T00:00:00.000 SCET.  This data approximates a time series
of charged particle fluxes from a selection of channels available
from the instrument.  The word approximates is used because
the angle scanning modes of the instrument complicates the
nature of the data.  At times the instrument mechanically scans,
and at times it is fixed to look at a specific direction.
With the type of data given here, the fluxes are angle averaged
for those time periods when the instrument is scanning, and are
time averaged over an arbitrary period (12 or 24 sec, see below)
for the periods when the detectors are stationary. The angle
averaged records represent periods of time equal to 48 or 96
sec (see below). This kind of data presentation has been called
the LECP Scan data. Another form that is also available is
the LECP Step data that gives the angle distributions sampled
during the scanning periods.

   Three scanning situations occurred during the time of this
data. They are: 1) continuous 48 sec stepping (48 seconds for
each of 8 look directions for a total of 6.4 minutes per scan;
note that sector 8 is shielded with 2 mm Al), 2) a special
Neptune scan cyclic with the following sequence: 7, scan, 1, scan,
7, scan, scan, repeat; where the 7 and the 1 represent 5.2
minute periods when the instrument is fixed in sectors 7 or 1,
respectively, and where the word scan represents a period
of scanning (6 sec stepping for a total scan time of 48 sec);
and 3) periods when the detectors are fixed for more extended
periods in sector 7 (periods bracketing the ring plane crossings).
For this Neptune Scan data, the 6.4 minute scan records during
stepping mode (1) have been time averaged to 12.8 minute records.
Also, during stepping mode (2), the double scans that have no
fixed periods between them have been averaged together into
a single (96 sec) record.  The single scans represent 48 sec
records.  The schedule for the three stepping modes is as
follows:

       prior to day 236/1600 SCET:     Mode (1)
       236/1600 to 237/0239:           Mode (2)
       237/0239 to 237/0319:           Mode (3)
       237/0319 to 237/0503:           Mode (2)
       237/0503 to 237/0554:           Mode (3)
       237/0554 to 238/0400:           Mode (2)
       after 237/0400:                 Mode (1)

Obviously these stepping mode changes, and the angle sample
switching that occurs during stepping mode (2), gives the data
a disjointed appearance.

     Two channel sample modes also occurred during the Neptune
encounter.  These two modes affect this data set only by changing
the primary record time length for the LECP Experiment Data Records
(EDR's). These time lengths have, in turn, been utilized for the
averaging times of this data set for non-stepping periods.  The
schedule is:

      prior to day 237/0200 SCET:  Far Encounter (24 sec records)

      237/0200 to 237/0551:        Near Encounter (12 sec records)

      after 237/0551:              Far Encounter (24 sec records)

     The LECP channels utilized with this data set are:

       EB01:          electrons,  22 to  35 keV
       EB02:          electrons,  35  to  61 keV
       EB03:          electrons,  61 to  112 keV
       EB04:          electrons, 112 to 183 keV
       EG06-EG07:     electrons, 252 to 480 keV
       EG07-EG08:     electrons, 480 to 853 keV
       EG08-EG09:     electrons, 853 to 1200 keV
       PL01:          ions,       28 to  43  keV
       PL02:          ions,       43 to  80  keV
       PL03:          ions,       80 to 137  keV
       PL04:          ions,      137 to 215  keV
       PL05:          ions,      215 to 540  keV
       PL06:          ions,      540 to 990  keV
       PL07:          ions,      990 to 2140 keV
       PL08:          ions,     2140 to 3500 keV

Please note that 3 of the electron channels are derived from
4 of the instrumental channels by taking differences between
adjacent (in energy) channels.

     The channel data is given in units of intensity:
counts/(cm^2.sec.str.keV).  For the ions, it has been assumed
that they consist only of protons.  Intensity is derived from
the raw count rates via the relation:

                    I  =  CR/(eG.(E2-E1),

where eG is geometric factor times detector efficiency, and
(E2-E1) is the band pass of the channel in energy.  The proton
values of these parameters were used in deriving the intensities
for this data set.  To obtain the Intensities under the assumption
that some other mass species dominates, one must convert back
to count rate (CR) utilizing the proton parameters, and then
convert to intensity using the parameters corresponding to the
mass species in question.  The parameters can be found in
Table 1 of Krimigis et al. (Journal of Geophysical Research,
V. 86, page 8227, 1981)  The corresponding parameters for electrons
can be found in Mauk et al. (Journal of Geophysical Research,
V. 92, page 15283, 1987).  Prior to the conversion to intensity,
the count rates have been corrected for: (1) Background,
(2) electron contamination of the lower energy ion channels, and
(3) solar UV contamination of the lowest energy ion channel.

     The uncertainty parameters given with the data associated with
each channel (expressed as a percent) is the largest of the
two quantities: (i) one standard deviation Poisson statistical
error, and (ii) a percentage assigned by the data supplier
based on the amount of contamination correction that has been
performed on each data channel.

     Also supplied with each record of this data set is the
fraction of the data accumulations that correspond to each
of the 8 angle sectors. For example, during a sector 7 stow
period, this number will be 1.0 for sector 7  and 0.0 for all
of the other sectors.  A sector 9 has also been defined
corresponding to those accumulations with no known sector
assignment.

    Additionally supplied for each data channel a one bit code
that tells whether that channel had any accumulations at
all associated with it (1 = yes; 0 = no).  This code must be
used to distinguish between accumulations that yielded no counts
and situations where the channel simply had no accumulations
(results in Intensity = 0.0).

    SAMPLING_PARAMETER_NAME        = TIME
    SAMPLING_PARAMETER_RESOLUTION  = 24.0
    MINIMUM_SAMPLING_PARAMETER     = N/A
    MAXIMUM_SAMPLING_PARAMETER     = N/A
    SAMPLING_PARAMETER_INTERVAL    = 24.0
    MINIMUM_AVAILABLE_SAMPLING_INT = 6.0
    SAMPLING_PARAMETER_UNIT        = SECOND
    DATA_SET_PARAMETER_NAME        = PARTICLE FLUX INTENSITY
    NOISE_LEVEL                    = N/A
    DATA_SET_PARAMETER_UNIT        = COUNTS/(CM**2*SECOND*STERRADIAN*KEV)

Confidence note for the PDS Neptune LECP Scan data.

    High quality data is available from the LECP instrument
throughout the time period addressed with this data set.
The data is subject to errors associated with Poisson
statistics and associated with various kinds and levels of
contamination. The known contaminations are: i) penetrating
background, ii) Solar UV contamination within the lowest energy
ion channel when the detector faces sunward, and iii) electron
contamination of the lower energy ion channels (the contaminating
electrons are measured).  Corrections have been made to the data
in attempts to remove the effects of these contaminations.

     An error parameter is given for each particle intensity
value given in the data set.  This error is expressed as a
percentage.  This number is the larger of the following
items: 1) the one standard deviation Poisson error, and 2) a
value assigned by the data supplier associated with the degree
of correction that was required with regard to the contaminations
listed above.

     Missing data is indicated with a binary flag associated
with each energy channel. Each channel's flag will read 1
if at least one instrumental accumulation occurred for that
channel and for that record.  The flag reads 0 for no
accumulations.  This parameter must be utilized to distinguish
between accumulations that yielded no counts, and the situation
where there simply were no accumulations (the error parameter
reads 100 for both cases).