IMP-8 MERGE Data User Information |
The IMP-8 satellite was launched on 26 October 1973 into a nearly circular orbit about the Earth at a radius ~35 Earth radii. IMP-8 spends 60+% of each orbit in the solar wind, with the rest of the time in the magnetosheath/magnetosphere. It is a spin-stabilized spacecraft, with its spin vector nearly perpendicular to the ecliptic plane, and a spin rate of 24 rpm.
The purpose of the MERGE program is to combine or merge data from four
instruments on IMP-8. A so-called MERGE record contains these data on
a time resolution of 20 seconds. The four IMP-8 experiments whose data
are part of the MERGE data set include two energetic charged particle
measurement instruments, a magnetic field measurement instrument, and
a solar wind plasma measurement instrument. Brief descriptions of the
four experiments are given below.
Instruments
The following sections I-IV contain summary information for the four instruments whose data are contained in a MERGE record. Instrument summary descriptions are adapted from those on file at NSSDC site IMP-8 Project Information.
CPME Summary Description:
Three solid-state detectors in an anticoincidence plastic
scintillator observe electrons between 0.2 and 2.5 MeV;
protons between 0.3 and 500 MeV; alpha particles between 2.0
and 200 MeV; heavy particles with Z values ranging from 2 to
5 with energies greater than 8 MeV; heavy particles with Z
values ranging between 6 and 8 with energies greater than
32 MeV; and integral protons and alphas of energies greater
than 50 MeV/nucleon, all with dynamic ranges of 1 to 1E+06
particles per (sq cm-s-sr). Five thin-window Geiger-Mueller
tubes observe electrons of energy greater than 15 keV,
protons of energy greater than 250 keV, and X-rays with
wavelengths between 2 and 10 A, all with a dynamic range
of 10 to 1E+08 per (sq cm-s-sr). Particles and X-rays,
primarily of solar origin, are studied, but the dynamic
range and resolution of the instrument also permits
observation of cosmic rays and magnetotail particles.
Further Information:
(i) Sarris, E. T. et al., J. Geophys. Res., v. 81, p. 2341, 1976.
(ii) T. P. Armstrong et al., J. Geophys. Res., v. 83, p. 5198, 1978.
Current P.I.: D.J. Williams (JHU/APL) JHU/APL IMP-8 CPME and EPE Home Page
(EPE data used: approx. 20 sec. time res.)
EPE Summary Description:
The purposes of this investigation are (1) to study the
propagation characteristics of solar cosmic rays through the
interplanetary medium over the energy ranges indicated below,
(2) to study electron and proton fluxes throughout the geomag
netic tail and near the flanks of the magnetosphere, and (3) to
study the entry of solar cosmic rays into the magnetosphere.
The instrumentation consists of a three-element telescope using
fully depleted surface-barrier solid-state detectors and a magnet
to deflect electrons. Two side-mounted detectors are used to
measure the deflected electrons. Two additional detectors in
separate mounts are used to measure charged particles above
15 keV (detector F), Z greater than or equal to 2 above 0.6 MeV
(detector G1) and above 1.0 MeV (detector G2), and Z greater
than or equal to 3 above 2.0 MeV (detector G3). The telescope
measures protons in three ranges between 2.1 and 25 MeV;
Z greater than or equal to 1 in three ranges between 0.05 and
2.1 MeV; alpha particles between 8.4 and 35.0 MeV in two ranges;
Z greater than or equal to 2 between 2.2 and 8.4 MeV; and
a background channel. Deflected electrons are measured in
two ranges between 30 and 200 keV.
Further Information:
D. J. Williams, NOAA Technical Report ERL 393-SEL 40, October 1977.
Current P.I.: R. P. Lepping (NASA/GSFC)
IMP-8 Magnetometer Home Page
Original data source:
NSSDC Anonymous FTP Site (MAG data used: 15.36 sec. time res.)
MAG Summary Description:
This experiment consists of a boom-mounted triaxial flux-
gate magnetometer designed to study the interplanetary and
geomagnetic tail magnetic fields. Each sensor has three
dynamic ranges of plus or minus 12, plus or minus 36, and
plus or minus 108 nT. With the aid of a bit compaction
scheme (delta modulation), 25 vector measurements are made
and telemetered per second. The experiment operated normally
from launch until mid-1975. On July 11, 1975, because of a
range indicator problem, the experiment operation was frozen
into the 36-nT range. The digitization accuracy in this range
is about plus or minus 0.3 nT. On March 23, 1978, the sensor
flipper failed. After that time, alternative methods of
Z-axis sensor zero-level determination were required.
Current P.I.: A. J. Lazarus (MIT)
MIT Space Plasma Group IMP 8 Home Page
Original data source:
Fine Resolution Data (PLS data used: approx. 1 min. time res.)
PLS Summary Description:
A modulated split-collector Faraday cup, perpendicular to
the spacecraft spin axis, is used to study the directional
intensity of positive ions and electrons in the solar wind,
transition region, and magnetotail. Electrons are studied
in eight logarithmically equispaced energy channels between
17 eV and 7 keV. Positive ions are studied in eight channels
between 50 eV and 7 keV. A spectrum is obtained every eight
spacecraft revolutions. Angular information is obtained in
either 15 equally spaced intervals during a 360-deg revolution
of the satellite or in 15 angular segments centered
more closely about the spacecraft-sun line.