ISEE 1 Plasma wave experiment (PWE) Spectrum Analyzer - Rapid Sample

'The ISEE-1 and -2 Plasma Wave Investigation' D. A. Gurnett, F. L. Scarf, R. W. Fredricks, and E. J. Smith, IEEE Transactions on Geoscience Electronics, Vol. GE-16, p. 225-230, 1978. The International Sun-Earth Explorer (ISEE) Program consisted of three satellites intended to study the Earth's magnetosphere and the solar wind. ISEE-1 and ISEE-2 were launched on October 22, 1977 into highly elliptical geocentric orbits. The satellites passed through the magnetosphere and into the magnetosheath during each orbit. ISEE-3 was launched on August 12, 1978 and subsequently inserted into a 'halo orbit' about the the libration point situated about 240 earth radii (Re) upstream between the earth and the sun. Plasma passing this point arrives at the Earth about one hour later where it may cause changes that can be observed by ISEE 1 and ISEE-2. These two spacecraft, separated by a variable distance and with similar instrument complements, were intended to resolve the space-time ambiguity associated with measurements by a single spacecraft on thin boundaries which may be in motion such as the bow shock and the magnetopause. ISEE-1 and ISEE-3 were the principal U. S. contributions to the International Magnetospheric Study. ISEE-2 was built and managed by the European Space Agency. In September 1982 ISEE-3 was diverted from its 'halo orbit' to explore the earth's deep tail region through much of 1983 on its way to an encounter with the comet Giacobini Zinner in September 1985. ISEE-1 had a complement of thirteen experiments to measure the waves, fields, plasma, and particles. The University of Iowa Plasma Wave Instrument (PWI) was one of these thirteen. The ISEE-1 plasma waves instrument provided a comprehensive determination of wave characteristics over a broad frequency range, including high-frequency resolution spectrum scans, simultaneous high-time resolution electric and magnetic frequency spectrum measurements, wave normal and Poynting flux measurements, and wide-band waveform measurements. PWI sampled the environment using three electric dipole antennas with lengths of 215, 73.5, and 0.61 meters for electric-field measurements, and a triaxial search coil antenna with three 16-in high permeability mu-metal cores each wound with 10,000 turns of wire and a preamplifier for magnetic-field measurements. The experiment's main electronics consisted of four main elements: 1) a narrow-band sweep frequency receiver, 2) a pair of high time resolution spectrum analyzers, 3) a wave normal analyzer, and 4) an analog waveform receiver (also called a wide-band receiver). These elements could be electrically connected to the six antennas in various combinations in flight. Data for this file originate with an electric antenna and were measured via the Electric Spectrum Analyzer (ESA). The PWI ESA was designed to provide high time resolution spectrum measurements for resolving wave emissions that are bursty or of a nonlinear nature. The ESA was a 20-channel analyzer covering the range from 5.62 Hz to 311 kHz. It had a relatively coarse frequency resolution, with four frequency channels per decade and bandwidths of +/-15 percent up to 10 kHz and +/-7.5 percent for 10 kHz and above. The ESA was nominally intended for electric field measurements, though 2.2 percent of all ESA measurements were made using the Z-axis magnetic search coil. The ISEE spacecraft collected two separate data products with the PWI ESA. 1) A full frequency range 20-channel spectra and 2) a single-channel, rapid-sample series. The 'E_series' variable in this file provides ESA rapid-sample measurements. Full frequency range 20-channel spectra are provided in a companion file set. The rapid-sample series data were collected at 8-times the data rate of the 20-channel spectra, thus there are 32 samples per second in high rate telemetry mode and 4 per second in low-rate mode. Regardless of the telemetry mode, every 16 seconds the rapid sample channel is incremented until reaching the highest frequency band of the ESA (311 kHz), where it rolls over to the 5th band (56.2 Hz). Only the upper 16 channels of the ESA were sampled in this manner. Altogether this provides a 16-channel frequency sweep every 4 minutes and 16 seconds. Unlike the SFR data, the time to preform a complete frequency sweep is not affected by the telemetry mode, though the number of samples in a sweep does increase by a factor of 4. Given the slowly changing nature of the frequency channel compared to the sampling time these data are stored as a time series, with the current frequency relegated to a status variable. Nonetheless, frequency-time spectrograms may be constructed from these measurements if desired. For a detailed description of the Plasma Wave Instrument, the reader is referred to the IEEE Geoscience Electronics reference above. A common acronym for the plasma waves instrument in older documentation is GUM, which stands for for Gurnett Mother. Since this acronym is not easily recognizable by the space physics community and since no official acronym is provided in the instrument paper, the more common short hand 'PWI' is used to refer to the Plasma Wave Instrument in this archive.

Tags: spectrum, waves-passive
Organization: National Aeronautics and Space Administration