Radar target identification using the bispectrum: a comparativestudy

Radar target identification is performed using time-domain bispectral features. The classification performance is compared with the performance of other classifiers that use either the impulse response or frequency domain response of the unknown target. The classification algorithms developed here are based on the spectral or the bispectral energy of the received backscatter signal. Classification results are obtained using simulated radar returns derived from measured scattering data from real radar targets. The performance of classifiers in the presence of additive Gaussian (colored or white), exponential noise, and Weibull noise are considered, along with cases where the azimuth position of the target is unknown. Finally, the effect on classification performance of responses horn extraneous point scatterers is investigated     

Ulysses solar wind observations to 56° south

In the 25 months since Jupiter flyby, the Ulysses spacecraft has climbed southward to a heliolatitude of 56°. This transit has been marked by an evolution from slow, dense coronal streamer belt solar wind through two regions where the rotation of the Sun carried Ulysses back and forth between streamer belt and polar coronal hole flows, and finally into a region of essentially continuous fast, low density solar wind from the southern polar coronal hole. Throughout these large changes, the momentum flux normalized to 1 AU displays very little systematic variation. In addition, the bulk properties of the polar coronal hole solar wind are quite similar to those observed in high speed streams in the ecliptic plane at 1 AU. Coronal mass ejections and forward and reverse shocks associated with corotating interaction regions have also been observed at higher heliolatitudes, however they are seen less frequently with increasing southern heliolatitude. Ulysses has thus far collected data from 20° of nearly contiguous solar wind flows from the polar coronal hole. We examine these data for characteristic variations with heliolatitude and find that the bulk properties in general show very little systematic variation across the southern polar coronal hole so far.     

Communication System Architecture for Air Traffic Management and Weather Information Dissemination

The authors present the communication system architecture for air traffic management and weather information dissemination as viewed within the context of the overall National Airspace System (NAS) and the services it provides. This presents the architecture in the 2015 time frame when the final phases of transition take place from analog voice to digital data exchange of common data via integrated networks. The results of this transition are an integrated collection of systems and procedures that efficiently use the capacity of the NAS while balancing access to all user classes and maintaining the highest levels of safety. Efficient collaboration among users is built on a foundation of common data. This information base provides common situational awareness to all participants. All users are accommodated and will receive benefits commensurate with equipage level. This architecture development provides a technical framework for decision-making, research, and analysis of communication technologies     

Gamow and the physics and evolution of stars

The high temperature sensitivity of thermonuclear reactions and the neurrino emission at the final stages of stellar evolution (urca process) are the most crucial Gamow's contribution to the physics and evolution of stars. G. Gamow made one of a few first attempts in astrophysics to get a comprehensive picture of stellar evolution from the main sequence (thenormal stars in his terminology) through the formation of white dwarfs, gravitational collapse of stellar cores and supernova explosions.     

Comparison of two theories of angle glint: polarization considerations

Angle glint can be explained as distortions in the radar echo signal phase front, or alternatively, deviations of the direction of power flow from the radial direction. Here we show that these two theories yield identical results when the polarization of the scattered waves and the receiving antenna are considered.     

Venus Express: Scientific goals, instrumentation, and scenario of the mission

The first European mission to Venus (Venus Express) is described. It is based on a repeated use of the Mars Express design with minor modifications dictated in the main by more severe thermal environment at Venus. The main scientific task of the mission is global exploration of the Venusian atmosphere, circumplanetary plasma, and the planet surface from an orbiting spacecraft. The Venus Express payload includes seven instruments, five of which are inherited from the missions Mars Express and Rosetta. Two instruments were specially designed for Venus Express. The advantages of Venus Express in comparison with previous missions are in using advanced instrumentation and methods of remote sounding, as well as a spacecraft with a broad spectrum of capabilities of orbital observations.     

A 6 D.O.F. opto-inertial tracker for virtual reality experiments in microgravity.

Gravity plays a role in many different levels of human motor behavior. It dictates the laws of motion of our body and limbs, as well as of the objects in the external world with which we wish to interact. The dynamic interaction of our body with the world is molded within gravity's constraints. The role played by gravity in the perception of visual stimuli and the elaboration of human movement is an active research theme in the field of Neurophysiology. Conditions of microgravity, coupled with techniques from the world of virtual reality, provide a unique opportunity to address these questions concerning the function of the human sensorimotor system. The ability to measure movements of the head and to update in real time the visual scene presented to the subject based on these measurements is a key element in producing a realistic virtual environment. A variety of head-tracking hardware exists on the market today, but none seem particularly well suited to the constraints of working with a space station environment. Nor can any of the existing commercial systems meet the more stringent requirements for physiological experimentation (high accuracy, high resolution, low jitter, low lag) in a wireless configuration. To this end, we have developed and tested a hybrid opto-inertial 6 degree-of-freedom tracker based on existing inertial technology. To confirm that the inertial components and algorithms will function properly, this system was tested in the microgravity conditions of parabolic flight. Here we present the design goals of this tracker, the system configuration and the results of 0g and 1g testing.     

Effects of test vehicle patterns on cellular coverage measurements

Mobile test systems intended for cellular phone coverage measurements suffer from uncertainties, which are caused by the unpredictable radiation pattern of the measuring antenna installation. Not only do adjacent structures and very common multiple antennas disturb the characteristics, but also in the case of an ideal position does the vertical lobing introduce errors exceeding 10 dB. The problems are likely to be worse in dense urban areas, where multipath from surrounding buildings is the dominating propagation mode     

Local-area helioseismology as a diagnostic tool for solar variability

Dynamical and thermal variations of the internal structure of the Sun can affect the energy flow and result in variations in irradiance at the surface. Studying variations in the interior is crucial for understanding the mechanisms of the irradiance variations. “Global” helioseismology based on analysis of normal mode frequencies, has helped to reveal radial and latitudinal variations of the solar structure and dynamics associated with the solar cycle in the deep interior. A new technique, - “local-area” helioseismology or heliotomography, offers additional potentially important diagnostics by providing three-dimensional maps of the sound speed and flows in the upper convection zone. These diagnostics are based on inversion of travel times of acoustic waves which propagate between different points on the solar surface through the interior. The most significant variations in the thermodynamic structure found by this method are associated with sunspots and complexes of solar activity. The inversion results provide evidence for areas of higher sound speed beneath sunspot regions located at depths of 4–20 Mm, which may be due to accumulated heat or magnetic field concentrations. However, the physics of these structures is not yet understood. Heliotomography also provides information about large-scale stable longitudinal structures in the solar interior, which can be used in irradiance models. This new diagnostic tool for solar variability is currently under development. It will require both a substantial theoretical and modeling effort and high-resolution data to develop new capabilities for understanding mechanisms of solar variability.     

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.