• Data Set Overview

• =================

• Description of the PDS LECP Neptune Scan Data

• =============================================

This Encounter Data Set consists of Resampled Electron and Ion Counting Rate Data from the Low Energy Charged Particle (LECP) Experiment on Voyager 2 while the Spacecraft was within the Vicinity of Neptune.

The Period covered is 1989-08-24T00:00:00.000 SCET to 1989-08-27T00:00:00.000 SCET.

These Data include Scan Plane Angle Distributions for those Periods when the LECP Instrument was mechanically scanning. There are Periods when the Instrument was not scanning, and the corresponding Data do not appear here with these Step Data.

These Data approximate a Time Series of Charged Particle Fluxes from a Selection of Channels available from the Instrument. The word "approximate" 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 s or 24 s, see below) for the Periods when the Detectors are stationary. The angle averaged Records represent Periods of Time equal to 48 s or 96 s (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 these Data were collected. They are:

• 1. Continuous 48 s Stepping (48 s for each of eight Look Directions for a Total of 6.4 min per Scan. Note that Sector 8 is covered by a 2 mm Aluminium Shield)
• 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 min Periods during which the Instrument is fixed in Sector 7 or Sector 1, respectively, and where the word "Scan" represents a Period of Scanning (6 s Stepping for a total Scan Time of 48 s)
• 3. Periods when the Detectors are fixed for more extended Periods in Sector 7 (Periods bracketing the Ring Plane Crossings)

For these Neptune Step Data, the 6.4 min Full Scan Records during Stepping Mode (1) have been averaged to 12.8 min Records. Also, during Stepping Mode (2), the Double Scans that have no fixed Periods between them have been averaged together into a single (96 s) Record. The Single Scans represent 48 s Records.

The Schedule of Stepping Mode Changes is as follows:

+-------------------------------------------------------------+
| Time Interval | Mode Setting |

| Prior to Day 236 at 1600 SCET | Mode (1) |
| Day 236 at 1600 SCET to Day 237 at 0239 SCET | Mode (2) |
| Day 237 at 0239 SCET to Day 237 at 0319 SCET | Mode (3) |
| Day 237 at 0319 SCET to Day 237 at 0503 SCET | Mode (2) |
| Day 237 at 0503 SCET to Day 237 at 0554 SCET | Mode (3) |
| Day 237 at 0554 SCET to Day 238 at 0400 SCET | Mode (2) |
| After Day 237 at 0400 SCET | Mode (1) |
+-------------------------------------------------------------+

Please note that the change over between Modes is not instantaneous, and that for a few Minutes the State of the Scanning is not regular. Note also that there were brief Interruptions to, and Changes in Time Phase in the Mode (2) Scan Cyclic during the Transitions into and out of the movable Block Period that bracketed the Close Approach Position (not shown above).

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 (EDRs). These Time Lengths have, in turn, been utilized for the Averaging Times of this Data Set for Non-Stepping Periods. The Schedule is:

+---------------------------------------------------------------------------------+
| Encounter Phase | Time Interval | Averaging Time |

| Far Encounter | Prior to Day 237 at 0200 SCET | 24 s |
| Near Encounter | Day 237 at 0200 SCET to Day 237 at 0551 SCET | 12 s |
| Far Encounter | After Day 237 at 0551 SCET | 24 s |
+---------------------------------------------------------------------------------+

The LECP Channels utilized with this Data Set are:

+-----------------------------------------+
| Channel | Particle | Energy Range |

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

Please note that three of the Electron Channels are derived from four of the Instrumental Channels by taking differences between adjacent Energy Channels.

The Channel Data is given in Units of Intensity: counts/(cm^2 s sr 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 equal to the Geometric Factor times the Detector Efficiency, and (E2-E1) is the Bandpass of the Channel in Units of 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. (J. Geophys. Res., 86, 8227, 1981). The corresponding Parameters for Electrons can be found in Mauk et al. (J. Geophys. Res., 92, 15,283, 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
• 3. Solar UV Contamination of the lowest Energy Ion Channel

• Parameters

• ==========

• Data Set Parameter PARTICLE FLUX INTENSITY

• ==========================================

+---------------------------------------------------------------------+
| Parameter Characteristics | Value |

| Sampling Parameter Name | TIME |
| Data Set Parameter Name | PARTICLE FLUX INTENSITY |
| Sampling Parameter Resolution | 24.000000 |
| Sampling Parameter Interval | 24.000000 |
| Minimum Available Sampling Int | 6.000000 |
| Data Set Parameter Unit | COUNTS/(CM^2SECONDSTERADIAN*KEV) |
| Sampling Parameter Unit | SECONDS |
+---------------------------------------------------------------------+

• Source Instrument Parameters
• ============================

+----------------------------------------------------------------+
| Parameter Characteristics | Value |

| Instrument Host ID | VG2 |
| Data Set Parameter Name | PARTICLE FLUX INTENSITY |
| Instrument Parameter Name | PARTICLE MULTIPLE PARAMETERS |
| Important Instrument Parameters | 1 |
+----------------------------------------------------------------+

• Processing

• ==========

• Processing History

• ==================

+---------------------------------------------------------------+
| Parameter Characteristics | Value |

| Source Data Set ID | N/A |
| Software | UNK |
| Product Data Set ID | VG2-N-LECP-4-SUMM-SCAN-24SEC-V1.0 |
+---------------------------------------------------------------+