An Application of Evidential Networks to Threat Assessment

Decision makers operating in modern defence theatres need to comprehend and reason with huge quantities of potentially uncertain and imprecise data in a timely fashion. An automatic information fusion system is developed which aims at supporting a commander's decision making by providing a threat assessment, that is an estimate of the extent to which an enemy platform poses a threat based on evidence about its intent and capability. Threat is modelled by a network of entities and relationships between them, while the uncertainties in the relationships are represented by belief functions as defined in the theory of evidence. To support the implementation of the threat assessment functionality, an efficient valuation-based reasoning scheme, referred to as an evidential network, is developed. To reduce computational overheads, the scheme performs local computations in the network by applying an inward propagation algorithm to the underlying binary join tree. This allows the dynamic nature of the external evidence, which drives the evidential network, to be taken into account by recomputing only the affected paths in the binary join tree.     

Ozone mini-hole observation over the Balkan Peninsula in March 2005

Areas with dimensions of 1000–3000 km in which the total ozone content (TOC) decreases fast are called ozone mini-holes. They are generated mainly dynamically in two ways, either by poor-ozone air mass transport from the tropics to higher latitudes by planetary wave activity or, they are connected with strong adiabatic uplifting of the tropopause height. An ozone mini-hole, generated by the second mechanism, was observed over the Balkan Peninsula on 19/21 March 2005. In the middle of March, the polar vortex was strongly disturbed by Rossby waves, reaching up to the lower stratosphere. Warming episodes over a geographical area, covering the Barents Sea and the Polar Sea north from Central Siberia, displaced a polar vortex fragment extremely southwards. However, the vorticity was weak and the stratospheric temperatures did not reach low values, providing conditions for ozone chemical destruction via heterogenic reactions. At the same time, a Rossby wave ridge was located below the European polar fragment. In the period from 13 to 19 March, the thermal tropopause over Sofia was uplifted almost by 3 km. Ozone distributions observed by the SCIAMACHY instrument on 18–21 March show a fast TOC decrease westwards from Ireland, which was moving eastwards during the next days, increasing the area in which the ozone content decreased. On 20/21 March low ozone content was observed above the Stara Zagora (42°N, 25°E) ground-based station by means of the GASCOD instrument, using DOAS technique. The TOMS Earth probe instrument detected 237 DU over Sofia. This is a record low March value from the beginning of the TOMS instrument measurements in 1978. In March/April the ozone distribution was characterized by its mean annual maximum of 360 DU at 42°N.     

Random walk of magnetic field lines: Subdiffusive,diffusive, and superdiffusive regimes

One- and two-dimensional models of magnetic field fluctuations and turbulence are widely used in space-, astrophysical, and laboratory contexts. In the present article we use a generalized form of the turbulence wave spectrum to calculate field line diffusion coefficients analytically and numerically. General conditions are derived for which field line wandering behaves subdiffusively, diffusively, and superdiffusively.     

CWLFM Radar for Ship Detection and Identification

Continuous wave lineal frequency modulated (CWLFM) radar presents some interesting advantages for coast surveillance and control as well as low probability of interception (LPI). This paper presents real results obtained with a radar prototype and processed with ISAR techniques. Also, results of an automatic ship identification system applied to simulated ISAR images are exposed. Moreover, radar behavior with unfavorable meteorological conditions is discussed     

Pop-up threat models for persistent area denial

Pop-up threats usually appear or disappear randomly in a battle field. If the next pop-up threat locations could be predicted it would assist a search or attack team, such as in a persistent area denial (PAD) mission, in getting a team of unmanned air vehicles (UAVs) to the threats sooner. We present a Markov model for predicting pop-up ground threats in military operations. We first introduce a general Markov chain of order n to capture the dependence of the appearance of pop-up threats at previous locations of the pop-up threats over time. We then present an adaptive approach to estimate the stationary transition probabilities of the nth order Markov models. To choose the order of the Markov chain model for a specific application, we suggest using hypothesis tests from statistical inference on historical data of pop-up threat locations. Anticipating intelligent responses from an adversary, which might change its pop-up threat deployment strategy upon observing UAV movements, we present adaptive Markov chain models using a moving horizon approach to estimate possibly abrupt changes in transition probabilities. We combine predicted and actual pop-up target locations to develop efficient cooperative strategies for networked UAVs. A theoretical analysis and simulation results are presented to evaluate the Markov model used for predicting pop-up threats. These results demonstrate the effectiveness of cooperative strategies using the combined information of threats and predicted threats in improving overall mission performance.     

Star recognition algorithm for APS star tracker: oriented triangles

An efficient star pattern recognition algorithm is presented. The purpose of this algorithm is to make sure of the compatibility of the software and the imaging sensor noise level. The new CMOS APS sensors have not currently reached the same accuracy as the former CCD sensors in position as well as in magnitude determination, especially in the dynamic stages. This algorithm allows the system to recognize the star pattern 20% faster than with reference algorithms. No false recognition has been noticed. Used databases have a size 5 to 10 times smaller, depending on other reference algorithms. Oriented triangles are used to compare the measured star pattern with the catalogue stars. The triangle's characterization criteria propose several solutions in a first time. A unique solution is selected by means of identification and validation methods in a second time. First results, presented hereinafter, are very encouraging, and this algorithm may be used in the future APS star trackers. APS star tracker robustness is significantly enhanced by this method during the critical navigation phases     

Correlations between GPS and USNO Master Clock time

The U.S. Naval Observatory Master Clock is used to steer the Global Positioning System (GPS) time. Time transfer data consisting of the difference between the Master Clock and GPS time has been acquired from all satellites in the GPS constellation covering a time period from 10 October 1995 to 12 December 1995. A Fourier analysis of the data shows a distinct peak in the Fourier spectrum corresponding to approximately a one day period. In order to determine this period more accurately, correlations are computed between successive days of the data, and an average of twenty five correlation functions shows that there exists a correlation equal to 0.52 at delay time 23 h 56 min, which corresponds to twice the average GPS satellite period. This correlation indicates that GPS time, as measured by the U.S. Naval Observatory, is periodic with respect to the Master Clock, with a period of 23 h and 56 min. An autocorrelation of a five day segment of data indicates that these correlations persist for four successive days     

Determination of the threshold acceleration for the gravitropic stimulation of cress roots and hypocotyls.

To determine the range of the threshold acceleration (a-threshold) for the gravitropic stimulation of Lepidium sativum L. roots and hypocotyls, experiments were performed on a centrifuge-clinostat with two-orthogonal axes. The rotation rate of the clinostat was 4 rpm (< or = 1.8 x 10(-4) g), while that of the centrifuge was from 3 to 17 rpm (3 x 10(-3) to 10(-1) g). The gravitropic response was determined: (i) after growth of roots and hypocotyls in their normal vertical position and subsequent gravitropic stimulation for 3 h by accelerations of 4 x 10(-3) to 10(-1) g, and (ii) after continuous stimulation in the lateral direction by centripetal accelerations of 4 x 10(-3) to 10(-1) g. The a-threshold was defined by an extrapolation of the regression line of R = p + rx, where x was either ln a or l/a for 3 h or a continuous stimulation, respectively. The a-threshold estimated after 3 h stimulation was equal to 2.6 x 10(-3) g for roots and 3.1 x 10(-3) g for hypocotyls. The threshold accelerations that were unable to evoke a gravitropic response even with continuous stimulation of cress roots and hypocotyls were approximately 3.1 x 10(-3) g and 3.6 x 10(-3) g, respectively. Increasing the stimulation acceleration up to 4.1 x 10(-3) g led to a statistically confirmed gravitropic response of a definite proportion of both the root and hypocotyl populations. In the experiments where acceleration and stimulation time were variable, the threshold dose (D-threshold) for roots was determined to be about 14 to 22 g x s, depending on the stimulation duration and the range of accelerations. The kinetics of gravitropic response at a near-threshold acceleration (4 x 10(-3) to 1.9 x 10(-2) g) differed from that at 1 g (horizontal stimulation). At low forces, the maximal response dependent on the magnitude of acceleration could not be enhanced by increasing the stimulation time up to at least 210 min.     

Effect of “Noisy” sun conditions on aircrew radiation exposure

In computer codes used to estimate the aircrew radiation exposure from galactic cosmic radiation, a quiet sun model is usually assumed. A revised computer code (PCAIRE ver. 8.0f) is used to calculate the impact of noisy sun conditions on aircrew radiation exposure. The revised code incorporates the effect of solar storm activity, which can perturb the geomagnetic field lines, altering cutoff rigidities and hence the shielding capability of the Earth’s magnetic field. The effect of typical solar storm conditions on aircrew radiation exposure is shown to be minimal justifying the usual assumptions.