A technique for enhanced slant range resolution for SAR systems inknowledge-based environment

Synthetic Aperture Radar (SAR) is an airborne (or spaceborne) radar mapping technique for generating high resolution maps of surface target areas including terrain. High resolution is achieved by coherently combining the returns from a number of radar transmissions. The resolution of the images is determined by the parameters of the emissions, with more data giving greater resolution. A requirement of the Microwave Radar Division's SAR radar is to provide classification of targets. This paper presents a technique for enhancing slant range resolution in SAR images by dithering the carrier centre frequency of the transmitted signal. The procedure controls the radar waveforms so they will optimally perform the classification function, rather than provide an image of best quality. It is shown that a Knowledge-Based engineering approach to determining the waveform of the radar gives considerably improved performance as a classifier of targets (of large radar cross-section), even though the corresponding image is degraded     

Reconstruction of mutilated speech

A system has been developed to enhance the quality of mutilated speech. A standard spectrogram analysis of the damaged speech is performed. The speech is then resynthesized as a sum of computer-generated sinusoids whose amplitudes and phases are derived partly from the given mutilated speech signal and partly from rules based on known properties of normal speech. The sinusoids selected are only approximate harmonics of the glottal pitch and are selected by a nonlinear, noncausal set of rules to reduce the nonspeech components in the synthesized speech output. The system has been shown to increase the quality of the mutilated speech appreciably     

Modeling of the radiation exposure during the flight of the second Bulgarian cosmonaut on board the Mir Space Station.

An experiment involving active detection of space radiation was carried out in the Space Research Institute (SRI) of Bulgarian Academy of Sciences, in preparation of the flight of the second Bulgarian cosmonaut. The radiations that would be encountered on the flight were modelled including solar and galactic cosmic rays and the particle radiation in the Earth's radiation belts. The dose rate was calculated for these different radiations behind the shielding of the space station. The variations in dose rates over the period of the flight were calculated and compared with measurements made during the orbit of the Mir Space Station. The calculated and measured dose rates agreed within 15-35%.     

External plasma flow and related geomagnetic phenomena

Considering a three layered configuration of boundary layer bounded by compressible magnetosheath and magnetospheric plasma, the dispersion equation for K-H instability has been derived. In the presence of finite compressibility normal components of wave vectors are non-zero implying propagation normal to the boundary layer. The growth rate for the magnetopause or M-mode is greater than the inner magnetospheric or I-mode surface waves. However, for certain orientations of magnetosheath magnetic field $\text{ωiIΩiM}$ and the corresponding phase and group velocities are significant. The amplitude ratio of displacement vectors at the magnetospheric and magnetosheath interfaces is greater for the I-mode than that for the M-mode. These situations are capable of exciting I-mode waves which may transport energy to the inner magnetosphere resulting in field line resonances and generation of micropulsations. The sense of polarization of M-mode and I-mode are the same in the magnetospheric region.     

The function of calcium in plant graviperception.

The fundamental question of gravitational biology is how do plants perceive a gravity. Recent experimental results have demonstrated that Ca second-messenger system has an essential role in induction of graviresponsiveness. Our data, that stimuli of various nature cause a rise of hyaloplasm Ca level revealed by means of pyroantimonate method, as well as complete inhibition of the gravitropism in roots of pea seedlings, provide indirect but consistent evidence of this role of Ca ions. A possible explanation for these results is that they may be due to an unbalanced and undirectional influx of Ca ions in statocytes from cell walls or from intracellular Ca stores, while in the presence of the Earths 1 g vector, this process occurs directionally, along this vector. It is possible that a target for the gravity stimulus is the flux mechanism of Ca to statocytes, including participation of the phosphatidylinositol system and calmodulin. The data that have become available from space flight experiments will be reviewed and an attempt will be made to compare these results with ground-based observations.     

Cometary/meteor coupling: structure of young streams.

Information on atmospheric parameters, properties and processes above 70 km are mainly based upon meteor data. An important problem of such data systematization is to single out the meteor streams associated with a series of extreme phenomena. The forecasting of these phenomena requires a physical model of meteor streams at the early stage of their occurrence. A direct coupling with comets is assumed for most of the streams. This paper analyses the structure simulation of cometary nucleus desintegration. The D-criterion is used as the orbital community criterion. Giacobini-Zinner comet in its ten appearances (1900-1979) is considered. Determination of stream location and its detailed structural characteristics is essential for long space missions.     

Military aircraft fiber optics networks: status & direction

Fiber optics is proving to be an essential transmission medium at data rates of 1 Gigabit per second and above because of advantages relative to copper, including increased distance-bandwidth, reduced weight, and reduced cable volume. Whereas implementation in commercial applications is often straightforward, aerospace applications present a number of challenges due to an environment harsher than exists in the commercial world. In order to meet the future needs of military aircraft, designers will have to choose carefully between a number of component and architectural choices now available. This paper examines current trends in aerospace fiber optics and maps future needs for aerospace.     

Assessment of safety in space power wiring systems

Wiring system failures have resulted from arc propagation in the wiring harnesses of many aircraft and space vehicles. These failures occur when the insulation becomes conductive upon the initiation of an arc. In some cases, the conductive path of the carbon arc track displays a high enough resistance such that the current is limited, and therefore may be difficult to detect using conventional circuit protection. Often, such wiring failures are not simply the result of insulation failure but are due to a combination of wiring system factors. Inadequate circuit protection, unreliable system designs, and careless maintenance procedures can contribute to a wiring system failure. This paper approaches the problem with respect to the overall wiring system, in order to determine what steps can be taken to improve the reliability, maintainability, and safety of space power systems. Power system technologies, system designs, and maintenance procedures which have contributed to past wiring system failures are discussed. New technologies, design processes, and management techniques which may lead to improved wiring system safety are introduced     

The dynamics of the object potential during electron beam injection and the possibility to control it

This review of the rocket and satellite experiments on electron beam injection in the height range of the ionosphere-magnetosphere shows a variety of manifestations of the positive charge potential on the body of the injector unit or in the space charge zone.

The possibilities of compensation are considered on the basis of theoretical models taking into account the beam-plasma collective interactions. The examples of numerical modeling of the charge-discharge dynamics are provided for the APEX conditions. It is shown that changing the pulse form and rise rate (dI/dt) one can change the structure of the space charge zone i.e. try to create the strong disturbance or resonance conditions in the time interval of πω_p≤ t ≤ t_ion. From these positions, we consider the APEX facilities used to control the inflow current, the spectrum of energetic particles, the high-frequency oscillations and the spatial distribution of optical emissions in the injector vicinity with high time resolution.