Frequency-Dependent Ionospheric Refraction Effects on the Doppler Shift of Satellite Signals

Analysis of four-frequency satellite Doppler data has allowed the separation and measurement of frequency-dependent ionospheric contributions to the Doppler shift, providing information useful in the study of errors incurred when tracking radio signals through the ionosphere. These refraction errors affect the accuracy of navigational position fixes obtained by Doppler satellite tracking systems. Some measured ionospheric refraction errors reported here are of interest because their magnitudes are significantly greater than those heretofore predicted from theoretical considerations.     

The observation of the galactic anticenter region by the balloon borne gamma-ray telescope Natalya-I

This paper presents the results of measurements of gamma radiation with energies above 5 MeV, from the galactic anticenter region. The balloon-borne gamma ray telescope “Natalya-I”, was launched on 6 November, 1980 from the Tata Institute of Fundamental Research's Balloon Facility (Hyderabad, India) and reached ceiling altitude of 35 km. The results on the accelerator calibration of the telescope, using a “tagged” gamma ray beam are also presented.     

A Comparison of Noncoherent and Coherent MTI Improvement Factors

An analysis based on statistical considerations and Monte Carlo simulations indicates that a noncoherent moving target indicator (MTI) using a linear envelope detector differs from one using a square law envelope detector. The square law envelope detector is usually described in the literature because of ease of analysis, and it is commonly stated or implied that the results are the same for the two cases because of the similar spectral characteristics of the detectors. A comparison is made between the two noncoherent MTIs and the coherent MTI in terms of clutter attenuation and MTI improvement factors.     

Observations of ultraviolet spectra of H II regions and galaxies with IUE

The ultraviolet spectra, obtained with the International Ultraviolet Explorer, of a sample of H II regions and the nuclear regions of spiral and elliptical galaxies are described. The star formation rates in the nuclei of spiral galaxies are similar to the star formation rate in the solar neighbourhood. The data indicate that the current thinking on the synthesis of carbon and nitrogen in galaxies has to be revised and the K-corrections determined from the ultraviolet spectra of galaxies when compared with the photometry of distant galaxies suggests colour evolution of galaxies at z > 0.3.     

On the role of meteoritic impacts in the formation of organic molecules

It is suggested that the UV radiation, and shock and plasma phenomena which accompanied the hypervelocity impacts of solid bodies (meteorites and comets) onto the surface of the young Earth may have contributed to the synthesis of prebiotic organic molecules in the primitive atmosphere in a larger amount than was thought previously. The mechanisms responsible for this synthesis are discussed using information obtained from recent experimental and theoretical work on macroscopic hypervelocity impacts.     

The instrument IKS and its calibration

The IKS infrared spectro-photometer will fly on board the VEGA platforms. It is designed to characterize the size, temperature and emissivity of the Comet Halley nucleus, to identify the major gaseous components of the inner coma and to detect the emission of the cometary grains. This paper presents the “calibration” experiments required to reduce the raw data: (i) absolute wavelength calibration of the filter wheels; (ii) modeling of the internal signal, as a function of the temperature of the different sub-systems; (iii) absolute and spectral responsivities of each of the spectrometric and photometric channels, as a function of the wavelength and position of the source in the field of view. Finally, we shall indicate the expected S/N ratios.     

An approximation of the height of the O+ - H+ transition level for use in IRI

A set of data including over 1400 transition level (TL) encounters of the OGO-6 satellite is used to construct analytical presentations of this altitude upon dip-latitude and longitude. The formula represents the TL variation between ± 50° dip-latitude and 20 h and 04 h local time interval. The data were obtained in the high solar activity period in 1969 and 1970.     

The microlesion concept in HZE particle dosimetry.

High energy, high-Z (HZE) particles are present in high-altitude and high-inclination satellite orbits. Most of the HZE dose above LET = 200 keV/micrometer is due to Fe nuclei. Individual HZE particles can damage several cells adjacent to one another along the particle track in tissue. The outcome has been described as a "microlesion" by D. Grahn. The present study attempts to define conditions for microlesions in specific tissues, to seek biological evidence that microlesions are produced, and to evaluate the microlesion as a potentially useful unit of dose in assessing hazards to spaceworkers. Microlesions in individuals cells and hair follicles have been described. Microbial studies have provided some evidence for independent secondary electron action. Whether or not a few hundred microlesions would be damaging to the whole organism depends upon the nature of damage to critical tissues. For example, cancer may occur if microlesions kill several cells in a straight line and mutate other cells alongside the particle track. Fe particle irradiation of the mouse Harderian gland (Fry et al., this issue) produces tumors efficiently. Microlesions in the lens, cornea, and retina need to be considered. Further dialogue is required before a final decision can be made concerning the most appropriate way to assess the HZE hazard.     

V.L.A. observations of flare build-up in coronal loops

Very Large Array (V.L.A.) measurements at 20 cm wavelength map emission from coronal loops with second-of-arc angular resolution at time intervals as short as 3.3 seconds. The total intensity of the 20 cm emission describes the evolution and structure of the hot plasma that is detected by satellite X-ray observations of coronal loops. The circular polarization of the 20 cm emission describes the evolution, strength and structure of the coronal magnetic field. Preburst heating and magnetic changes that precede burst emission on time scales of between 1 and 30 minutes are discussed. Simultaneous 20 cm and soft X-ray observations indicate an electron temperature $\text{T}{}_{\mathrm{e}}\textcolor{red}{}\text{2.5 × 10}{}^7\text{K}$ and electron density $\text{N}{}_{\mathrm{e}}\textcolor{red}{}\text{10}{}^{10}\text{cm}{}^{\mathrm{?3}}$ during preburst heating in a coronal loop that was also associated with twisting of the entire loop in space. We also discuss the successive triggering of bursts from adjacent coronal loops; highly polarized emission from the legs of loops with large intensity changes over a 32 MHz change in observing frequency; and apparent motions of hot plasma within coronal loops at velocities V > 2,000 kilometerspersecond.