The WHISPER sounder on the Cluster spacecraft is primarily designed to provide an absolute measurement of the total plasma density within the range 0.2–80 cm-3. This is achieved by means of a resonance sounding technique which has already proved successful in the regions to be explored. The wave analysis function of the instrument is provided by FFT calculation. Compared with the swept frequency wave analysis of previous sounders, this technique has several new capabilities. In particular, when used for natural wave measurements (which cover here the 2–80 kHz range), it offers a flexible trade-off between time and frequency resolutions. In the basic nominal operational mode, the density is measured every 28 s, the frequency and time resolution for the wave measurements are about 600 Hz and 2.2 s, respectively. Better resolutions can be obtained, especially when the spacecraft telemetry is in burst mode. Special attention has been paid to the coordination of WHISPER operations with the wave instruments, as well as with the low-energy particle counters. When operated from the multi-spacecraft Cluster, the WHISPER instrument is expected to contribute in particular to the study of plasma waves in the electron foreshock and solar wind, to investigations about small-scale structures via density and high-frequency emission signatures, and to the analysis of the non-thermal continuum in the magnetosphere.

Whisper, a resonance sounder and wave analyser: Performances and perspectives for the Cluster mission

On board the geostationary GEOS 2, a relaxation sounding (RS) experiment using a pulsed active wave technique has been operated in the frequency range 03--77 kHz In situ measurements of the equatorial magnetospheric electron density at Lapprox =6, obtained in the range from 01 to approx100 cm/sup -3/ through on line data processing, are presented The results from 4 months of routine operations (November 20, 1978--March 28, 1979) are statistically studied Many features of the density distributions at 66 R/sub E/ displayed from GEOS 2 RS data corroborate the morphological characteristics evidenced in past experimental data sets of magnetospheric density, like those from ground-based whistler observation and from embarked particle experiments In providing an improved accuracy-especially for the cold plasma density-and unique coverage in space and time, the GEOS 2 RS data set brings some extension of results The average properties of different magnetospheric regions that can be sampled at 66 R/sub E/ with respect to LT are focused; the dayside plasma trough, with a few cm/sup -3/ typically, the plasmaspheric bulge (a few tens of cm/sup -3/) and the associated plasmapause crossings (variations in cm/sup -3/ per minute), and the geosynchronous nightside where the density fluctuates in the lowermore » range available (01--1 cm/sup -3/) The important contribution of cold plasma to the dayside magnetospheric density is reported There are striking variabilities of the density distributions found from day to day, especially as far as the plasmaspheric bulge morphology is concerned Relationships between geomagnetic activity and both the LT position and the LT width of the bulge are found« less

Electron density and plasmapause characteristics at 6.6 RE : A statistical study of the GEOS 2 relaxation sounder data

The relaxation sounder uses the characteristics of the propagation of radiowaves to sound the plasma surrounding the spacecraft. It determines, in particular, the plasma frequency, which gives the electron density.

Plasma Density Measurements from the GEOS-1 Relaxation Sounder

Measurements of electric and magnetic wave fields and of cold plasma parameters on-board GEOS-1. Preliminary results

The French electron density experiment aboard the ISEE 1 and 2 satellites really consists of two separate, but complementary, experiments to measure the total electron density by means of radio techniques. Both experiments are new: one flew above the ionosphere for the first time on the satellite GEOS, launched in April 1977, while the other takes advantage of the unique ISEE feature of having two spacecraft which are always relatively close together. The principles and the realization of both experiments are described.

The ISEE Electron Density Experiment

The waveforms and envelopes of resonance signals observed in the ionosphere at 2, 3, 4, and 5fH by rocket experiment are compared with the analytical results provided by a spatial ray-tracing procedure which takes the gradient of Earth's magnetic field into account. An approximate calculation yields the algebraic expression of the wave damping from whence the decrease of the received signals is deduced versus time as well as their frequency variations.

B. Higel

Papers

Theoretical study of gyroresonances with application to rocket experiments