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991.
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 相似文献
992.
Committee on Space Policy H.Guyford Stever Laurence J. Adams Consultant Retired President William A. Anders Senior Executive Vice President Arden L. Bement Jr Vice President Joseph V. Charyk Chairman of the Board Retired Chairman CEO Richard N. Cooper Robert S. Cooper President Edward E. David Jr President John M. Logsdon Director Jeremiah P. Ostriker Director Samuel C. Phillips Retired General Elmer B. Staats Edward C. Stone Jr Vice President 《Space Policy》1989,5(3)
993.
994.
Kabrisky M. Rogers S.K. Bashir N.A. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(9):39-43
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 相似文献
995.
N G Dachev TsPMatviichuk YuN Bankov R T Koleva P I Vellinov L G Todorieva J V Semkova V M Petrov V I Redko M V Zil V G Mitrakas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):253-255
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%. 相似文献
996.
Staggered Costas Signals 总被引:1,自引:0,他引:1
A radar signal, based on coherent processing of a train of staggered Costas bursts, is suggested and investigated. The selection of sequences of each burst is based on a minimum number of collocation of their individual ambiguity function sidelobe peaks. The resulting ambiguity function combines qualities of both "thumbtack" and "bed of nails" signals. Comparison with linear-FM, V-FM, and complementary phase coded (CPC) signals is given, as well as comparison with hybrid signals consisting of both phase and frequency coding. 相似文献
997.
R.N. Singh R. Prasad V. Singh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):369-374
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 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. 相似文献
998.
N A Belyavskaya 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):83-91
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. 相似文献
999.
N V Kulikova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(4):67-70
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. 相似文献
1000.
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. 相似文献