Fusion of sensors with dissimilar measurement/tracking accuracies

The case of data fusion of sensors dissimilar in their measurement/tracking errors is considered. It is shown that the fused track performance is similar whether the sensor data are fused at the track level or at the measurement level. The case of a cluster of targets, resolved by one sensor but not the other, is also considered. Under certain conditions the fused track may perform worse than the worst of the sensors. A remedy to this problem through modifications of the association algorithm is presented     

Interaction of shocks with a current sheet and reconnection in the solar corona

Interaction of shocks with a current sheet is investigated within a 2D MHD model based on an improved FCT numerical scheme. Basic parameters of the problem are chosen to correspond to situations in the solar corona with low plasma β and moderate shock strength. Slow and fast MHD shocks are introduced with shock normal parallel to magnetic field lines. The interaction with the current sheet causes distortion of the shock front and this distorts the magnetic field lines and generates electric current. Large current densities are generated especially when the fast MHD shock becomes the intermediate MHD shock at the current sheet. Then peak values of the current density are about 3–4 times larger than the initial undisturbed values in the current sheet.     

Target detection and tracking with HF radar using reciprocal SARtechniques

Sustained research and development at Memorial University of Newfoundland has led to an operational High Frequency Ground Wave Radar (HF-GWR) system for coastal surveillance. This radar system has demonstrated over-the-horizon detection of targets such as vessels, ice hazards and low-flying aircraft, and performed ocean parameter measurements over a large area. The industrial developers of offshore hydrocarbon reserves in ice infested regions have an urgent requirement for the long range detection and tracking of icebergs from their production platforms. However, due to space restrictions, a rig- or ship-based system can only accommodate a compact antenna array. The uniform trajectory and low velocity of icebergs is ideal for Reciprocal Synthetic Aperture Radar (RSAR) processing with long target dwell times. The proven ice detection capability of HF-GWR systems, coupled with the compact antennas suggested by the RSAR technique, can be used to develop a rig- or ship-based all-weather surveillance device for ice hazards. It is also anticipated that the results of this research will allow the use of shorter antenna arrays for many other applications. Preliminary results using real data from the operational HF-GWR system are presented     

The future of space medicine.

In November 2000, the National Aeronautics and Space Administration (NASA) and its partners in the International Space Station (ISS) ushered in a new era of space flight: permanent human presence in low-Earth orbit. As the culmination of the last four decades of human space flight activities. the ISS focuses our attention on what we have learned to date. and what still must be learned before we can embark on future exploration endeavors. Space medicine has been a primary part of our past success in human space flight, and will continue to play a critical role in future ventures. To prepare for the day when crews may leave low-Earth orbit for long-duration exploratory missions, space medicine practitioners must develop a thorough understanding of the effects of microgravity on the human body, as well as ways to limit or prevent them. In order to gain a complete understanding and create the tools and technologies needed to enable successful exploration. space medicine will become even more of a highly collaborative discipline. Future missions will require the partnership of physicians, biomedical scientists, engineers, and mission planners. This paper will examine the future of space medicine as it relates to human space exploration: what is necessary to keep a crew alive in space, how we do it today, how we will accomplish this in the future, and how the National Aeronautics and Space Administration (NASA) plans to achieve future goals.     

Possible contribution of different energy sources to the production of organics in Titan's atmosphere.

A quantitative comparison of the products arising from the irradiation of a Titan's simulated atmosphere is presented. The energy sources used represent some of the main events that occur in the satellite's atmosphere. All of the compounds identified are classified in the hydrocarbon and nitrile chemical families. Almost all of the detected compounds in Titan's atmosphere are produced by one or more energy sources. The compounds with the highest energy yields include the C2 hydrocarbons, methanonitrile and ethanonitrile. The possibility of using some of the produced organics as tracer compounds during the Huygens descend to identify the leading energy form in the different atmospheric levels remains open.     

Infrared spectrometer PFS for the Mars 94 orbiter

Thin films containing a mixture of aliphatic (glycine) and aromatic (tryptophan or tyrosine) amino acids were exposed to a vacuum ultraviolet radiation (VUV) with wavelenghts 100–200 nm. Dipeptides (glycyl-tryptophan and glycyl-tyrosine) were synthesized in these conditions. We compared the actions of VUV and γ-radiation. Polymerization is an essential step in prebiological evolution and we have shown that this stage probably occured over an early Solar system history.     

Long-term modulation of Galactic Cosmic Radiation and its model for space exploration.

As the human exploration of space has received new attention in the United States, studies find that exposure to space radiation could adversely impact the mission design. Galactic Cosmic Radiation (GCR), with its very wide range of charges and energies, is particularly important for a mission to Mars, because it imposes a stiff mass penalty for spacecraft shielding. Dose equivalent versus shielding thickness calculations, show a rapid initial drop in exposure with thickness, but an asymptotic behavior at a higher shielding thickness. Uncertainties in the radiobiology are largely unknown. For a fixed radiation risk, this leads to large uncertain ties in shielding thickness for small uncertainties in estimated dose. In this paper we investigate the application of steady-state, spherically-symmetric diffusion-convection theory of solar modulation to individual measurements of differential energy spectra from 1954 to 1989 in order to estimate the diffusion coefficient, kappa (r,t), as a function of time. We have correlated the diffusion coefficient to the Climax neutron monitor rates and show that, if the diffusion coefficient can be separated into independent functions of space and time: kappa (-r,t)=K(t)kappa 0 beta P kappa 1(r), where beta is the particle velocity and P the rigidity, then (i) The time dependent quantity 1/K(t), which is proportional to the deceleration potential, phi(r,t), is linearly related to the Climax neutron monitor counting rate. (ii) The coefficients obtained from hydrogen or helium intensity measurements are the same. (iii) There are different correlation functions for odd and even solar cycles. (iv) The correlation function for the Climax neutron monitor counting rate for given time, t, can be used to estimate mean deceleration parameter phi(t) to within +/- 15% with 90% confidence. We have shown that kappa(r,t) determined from hydrogen and/or helium data, can be used to fit the oxygen and iron differential energy spectra with a root mean square error of about +/- 10%, and essentially independent of the particle charge or energy. We have also examined the ion chamber and 14C measurements which allow the analysis to be extended from the year 1906 to 1990. Using this model we have defined reference GCR spectra at solar minimum and solar maximum. These can be used for space exploration studies and provide a quantitative estimate of the error in dose due to changes in GCR intensities.     

Data fusion of decentralized local tracker outputs

An approach for fusing offboard track-level data at a central fusion node is presented. The case where the offboard tracker continues to update its local track estimate with measurement and system dynamics models that are not necessarily linear is considered. An algorithm is developed to perform this fusion at a central node without having access to the offboard measurements, their noise statistics, or the location of the local estimator. The algorithm is based on an extension of results that were originally established for linear offboard trackers. A second goal of this work is to develop an inequality constraint for selecting the proper sampling interval for the incoming state estimates to the fusion node. This interval is selected to allow use of conventional Kalman filter algorithms at the fusion node without suffering error performance degradation due to processing a correlated sequence of track state estimates     

High energy particle dispersion events observed by interball-1 and -2

Time period from October 1996 until January 1998 was checked on high energy resolution DOK2 energetic particle instrument measurements on Interball-1 and Interball-2 for the ion (> 20 keV) dispersive events (EDIS) with the exclusion of Interball-1 orbit parts in the tail. A variety of energy dispersive events, both in ion and electron spectra with different duration is found in the auroral regions, in the outer magnetosphere and near the cusp. While EDIS were observed in all sectors of MLT, the best conditions for their observation were in the afternoon local time. The characteristics of dispersive events observed by DOK2 are consistent with their explanation by the gradient-curvature drift of particles from the injection point(s) in the night local time sector given in Lutsenko at al., 2000a, b.     

Evolution of the sun''s near-surface asphericities over the activity cycle

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge — connecting the MDI seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MDI data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation — usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required.

We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal.