The low energy gamma-ray experiments on GRO in perspective

The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed.     

Wave measurements in active experiments on plasma beam injection

The paper presents the results and discussion of VLF wave measurements carried out in the course of two rocket experiments on injection of a dense cesium ion beam into the ionosphere at the heights of 165–240 km. The injection was accompanied by enhancement of the broad-band noise by several orders of magnitude. The wave measurements in the frequency range of 1–11 kHz revealed two pronounced frequencies somewhat exceeding that of the lower-hybrid resonance oscillations in the background plasma and the cesium beam. The oscillations were modulated by frequencies close to the ion-cyclotron frequencies of the background plasma.     

Enhanced crop discrimination using the mid-IR (1.55–1.75μm)

Improvements in crop discrimination can be realized by using mid-IR bands (1.55–1.75 μm and 2.08–2.35 μm) which are sensitive to canopy moisture content. Analyses of data from two growing seasons in Webster County, Iowa clearly indicate that corn and soybeans are highly separable in the mid-IR from early season through harvest. This contrasts sharply with visible and near-IR bands where corn and soybeans are confused throughout much of the growing season. The mid-IR temporal reflectance behavior appears to result from differences between C₄ monocot and C₃ dicot internal leaf structure. If this hypothesis holds, mid-IR observations should improve discrimination in other instances where similar differences in internal leaf structure are present.     

Ion signatures of reconnection at the magnetopause

For a rotational MHD discontinuity the bulk flow is Alfvénic in the de Hoffmann-Teller frame. Using AMPTE/IRM data, we present ion distribution functions during three crossings of the dayside low-latitude magnetopause. For these crossings a well defined de Hoffmann-Teller frame can be found, but the field-aligned bulk flow is always slower than the Alfvén speed. Nevertheless, we find signatures in the distribution functions that provide clear evidence for magnetic reconnection: solar wind ions reflected off the magnetopause, “D-shaped” solar wind ion distributions in the boundary layer, and counterstreaming of solar wind ions and ionospheric ions in the boundary layer.     

Ionospheric effects caused by barium releases

Results of experimental studies of the ionospheric effects produced by CRRES barium releases are considered. The experimental observations of HF spectral characteristics by Doppler method are made by a network of long distance radio paths intersecting the L-shell of releases. The time dependence of their occurrence relative to the moment of release and the character of changes of spectral parameters produces signal effects (SE) which may be classified as: the unique burst, the quasiperiodic group of bursts, the regular changes of spectral parameters and wave processes. Observed types of SE are analogous to those seen when the releases were produced at the heights from 140 to 160 km. The result of experimental observations testify that there are special geophysical phenomena produced by barium releases.     

An instrument for DC electric field and AC electric and magnetic field measurements aboard ‘Intercosmos-Bulgaria-1300’ satellite

The instrument IESP-IPMP represents the complex unit measuring the vector of the DC electric field, the vectors of the electric and magnetic field in the frequency range of 0.2 – 6.5 Hz (wave form), autocorrelation functions of waves with frequencies of 0.1 – 5 kHz, and wave amplitudes in 8 bandpass channels. Some results are shown and compared in the various frequency ranges.     

Capillary brazing under microgravity (TEXUS-II) and 1g conditions

Experiments of vacuum brazing under both microgravity and 1-g conditions show the effect of hydrostatic pressure on ga-filling. The absence of buoyancy forces under microgravity affects the microstructure of the solidified braze in the joint.     

Comparative analysis of Venusian ionosphere dual-frequency radio soundings with the satellites Venera-9, 10 and Pioneer-Venus

A comparison of the Venusian ionosphere electron density profiles obtained by the dual-frequency radio occultation method for the satellites Venera-9,10 (1975) and the Pioneer-Venus orbiter (1978–1979) has been carried out. It is shown that the general nature of the profiles, the main maximum heights and electron densities, the ionopause height positions determined with the satellites Venera-9, 10 on the one hand and Pioneer-Venus orbiter on the other hand are in good agreement. This fact testifies to the reliability of the experimental dual-frequency radio occultation data. An attempt to compare the radio occultation data with the direct measurements points out the essential contradictions between them, which need detailed analysis and discussion.     

Proposal for a reference model of the middle atmosphere of the southern hemisphere

Available rocketsonde information has been used to compile tables of monthly mean temperature, pressure, density and zonal wind for the middle atmosphere of the southern hemisphere with the purpose of revising similar tables presented to COSPAR earlier. The altitude range is 25 to 80 km in steps of 5 km. The latitude range is 0° to 70°S with a 10° step. The compatability of different sets of temperature measurements is discussed. Mean values of temperature, pressure and zonal wind obtained for the southern hemisphere are compared with northern hemisphere model values. Large differences between the hemispheres (up to 20°C in temperature, 20–30% in pressure, 30–50 m/s in wind) imply that reference atmospheres such as CIRA should be complemented by southern hemisphere climatology.