PDS_VERSION_ID = PDS3
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 80
FILE_RECORDS = 18785
^TABLE = "JPAMERG1.TAB"
DATA_SET_ID = "GIO-C-JPA-4-DDR-HALLEY-MERGE-V1.0"
TARGET_NAME = HALLEY
START_TIME = 1986-03-12T06:09:34.460
DESCRIPTION = "This table contains results from the Implanted Ion Sensor
(IIS) 4DH mode and the Fast Ion Sensor SW and HAR modes
of the Three-Dimensional Particle Analyser (JPA) experiment
on the GIOTTO space craft for the mission to comet
P/Halley. The results of the Fast Ion Sensor (FIS - inbound) and IIS
(outbound) have been merged with magnetometer results in this file. Values
are given for protons.
JPA FIS data are from two sources:
- up to March 13, 19:24:55 SCET, data are from the solar wind mode at 8
seconds time resolution. The moments are derived from data in a
45 x 45 degree field of view, centered on the nominal solar wind
direction. There is continuous converage in energy and angle. The
peak remains within this reduced field of view.
- March 13, 19:24:55 to 22:38:17 SCET, data are from the HAR mode at 24
second time resolution. This mode has an angular field of view
accepting ions from all directions except a 20 deg cone in the ram
direction. Energy-angle coverage is not contiguous in this mode so
an assumption is made to boost the counts in each bin to make the
distribution appear contiguous. The peak of the solar wind flux
alternates between the last two 26 deg bins during this period.
Moments are calculated for the regions of space sampled by the
detector, i.e. up to the 20 deg ram cone, with no assumption to increase
the range beyond this. After 19:24:55 on the inblound pass when the
HAR mode data are used, the values given should be divided by 3.2 to
take account of the bin sizes for HAR (see Coates, et al. (1990).
The following assumptions hold: FIS is an electrostatic analyser and so
cannot distinguish mass - except in the solar wind mode where the protons
and alpha particles are cold enough that they separate in energy/charge; in
HAR mode the moment is over the full FIS energy range so includes anything
(all protons).
JPA IIS data is from the 4DH mode. In this mode, the Time of Flight
measurement is combined with the energy level information provided by
the IIS to separate mass groups, e.g., 0-1.7 amu/q (presumably protons).
The moments are derived from data collected during one spacecraft spin,
i.e., 128 s, at each of 32 energy levels to obtain a complete distribution.
Pickup protons are included in the numbers but this is only a small effect.
The IIS temperature quoted on the outbound pass should be treated as a
relative value; by intercalibration with FIS on the inbound pass the
temperature in K is given by multiplying the numbers by a factor of 1000.
The 'JPAMERGE' file includes both FIS and IIS data. The JPA data up
to 22:38:17 are from FIS given every 8 s. (At this time the sampling
changes to every 64 s; only magnetometer values are listed in this interval.)
The JPA data starts again at approx 0104 on March 14 (MJD 13221 or
day 73), and is from the IIS 4DH mode. This data has a time resolution
of 128 seconds - in the merge file it is combined with 64s
magnetometer data, which is why there are two MAG points for every
JPA data repeated twice here. (The last 16 lines are again only
magnetometer values.) The end time of the data is 02:46:28 on March 15.
There are some differences in the timing and values shown in the JPAMERGE
file for the MAG data as shown in the following table:
Mag values JPA values Times Data gap filling
JPAMERG1 = = 0 None
JPAMERG2 Not = = -4.46s -999.9
MAG00001 = N/A +0.36s -999.9
The timing differences in the JPA data occur for 3 reasons:
(1) Use of beginning of bin or middle of bin
(2) Internal buffering of 0.5 sec in JPA
(3) Crossing time of the solar wind across the FIS field of view,
which occurs 0.25 sec after the beginning of a bin
The correct JPA times for a middle of bin could be retrieved by adding
3.75s to the times in JPAMERG1.
In the existing files:
- MAG data are averages at the middle of the time bin given in all
cases, which explains the difference in values (not noticeable
on a plot) in JPAMERG2. However the reason for the time
difference between JPAMERG1 and MAG00001 is unclear, it may be
an attempt to correct for the actual time of the solar wind
entering the FIS field of view.
- JPA data are beginning of bin in file JPAMERG1. In JPAMERG2
attempts were made to make the data middle of bin but
unfortunately 3.75s should have been added to the data as
mentioned above. This mistake could have occurred during
addition of data at other institutes.
Therefore, treat times as accurate to +/- 4s.
As data from both experiments were not available for the entire time
interval, missing datasets have been replaced by zeroes."
RECORD_FORMAT = "F14.8, F9.3, F8.3, F8.3, F6.2, F9.1, 3(F8.3)"
OBJECT = TABLE
NAME = "JPAMERG1_TABLE"
INTERCHANGE_FORMAT = ASCII
COLUMNS = 9
ROW_BYTES = 80
ROWS = 18785
DESCRIPTION = "This table contains velocity and magnetic field vectors
with related data, tagged with an observation time.
Coordinates are centered on the comet. A definition
of such an HSE coordinate system (right handed) follows:
x-axis towards sun, y-axis parallel to the ecliptic plane
and z-axis perpendicular to the ecliptic towards the N
celestial pole."
OBJECT = COLUMN
NAME = SC_EVENT_TIME
BYTES = 14
DATA_TYPE = ASCII_REAL
START_BYTE = 1
FORMAT = "F14.8"
UNIT = "MJD"
DESCRIPTION = "Spacecraft event time expressed as modified Julian date,
where 13220 is 13 March 1986."
END_OBJECT
OBJECT = COLUMN
NAME = PROTON_VX
BYTES = 9
DATA_TYPE = ASCII_REAL
START_BYTE = 15
FORMAT = "F9.3"
UNIT = "KM/S"
DESCRIPTION = "Proton X velocity component, HSE coordinate system"
END_OBJECT
OBJECT = COLUMN
NAME = PROTON_VY
BYTES = 8
DATA_TYPE = ASCII_REAL
START_BYTE = 24
FORMAT = "F8.3"
UNIT = "KM/S"
DESCRIPTION = "Proton Y velocity component, HSE coordinate system"
END_OBJECT
OBJECT = COLUMN
NAME = PROTON_VZ
BYTES = 8
DATA_TYPE = ASCII_REAL
START_BYTE = 32
UNIT = "KM/S"
FORMAT = "F8.3"
DESCRIPTION = "Proton Z velocity component, HSE coordinate system"
END_OBJECT
OBJECT = COLUMN
NAME = PROTON_NUMBER_DENSITY
BYTES = 6
DATA_TYPE = ASCII_REAL
START_BYTE = 40
FORMAT = "F6.2"
UNIT = "CM**-3"
DESCRIPTION = "Number density of protons"
END_OBJECT
OBJECT = COLUMN
NAME = PROTON_TEMPERATURE
BYTES = 9
DATA_TYPE = ASCII_REAL
START_BYTE = 46
FORMAT = "F9.1"
UNIT = "KELVIN"
DESCRIPTION = "Temperature of the protons, in Kelvin"
END_OBJECT
OBJECT = COLUMN
NAME = B_X
BYTES = 8
DATA_TYPE = ASCII_REAL
START_BYTE = 55
FORMAT = "F8.3"
UNIT = "NANOTESLA"
DESCRIPTION = "X component of magnetic field, HSE coordinate system"
END_OBJECT
OBJECT = COLUMN
NAME = B_Y
BYTES = 8
DATA_TYPE = ASCII_REAL
START_BYTE = 63
FORMAT = "F8.3"
UNIT = "NANOTESLA"
DESCRIPTION = "Y component of magnetic field, HSE coordinate system"
END_OBJECT
OBJECT = COLUMN
NAME = B_Z
BYTES = 8
DATA_TYPE = ASCII_REAL
START_BYTE = 71
FORMAT = "F8.3"
UNIT = "NANOTESLA"
DESCRIPTION = "Z component of magnetic field, HSE coordinate system"
END_OBJECT
END_OBJECT = TABLE /* JPAMERG1_TABLE */
END