Hypothesis-test-based landcover change detection using multi-temporal satellite images – A comparative study

Remote sensing images and technologies have been widely applied to environmental monitoring, in particular landuse/landcover classification and change detection. However, the uncertainties involved in such applications have not been fully addressed. In this paper two hypothesis-test-based change detection methods, namely the bivariate joint distribution method and the conditional distribution method, are proposed to tackle the uncertainties in change detection by making decisions based on the desired level of significance. Both methods require a data set of class-dependent no-change pixels to form the basis for class-dependent hypothesis test. Using an exemplar study area in central Taiwan, performance of the proposed methods are shown to be significantly superior to two other commonly applied methods (the post-classification comparison and the image differencing methods) in terms of the overall change detection accuracies. The conditional distribution method takes into consideration the correlation between digital numbers of the pre- and post-images and the effect of the known pre-image digital number on the range of the post-image digital number, and therefore yields the highest change detection accuracy. It is also demonstrated that the class-dependent change detection is crucial for accurate landuse/landcover change detection.     

Design calculation of superlight piston-engined aircraft flight characteristics

Algorithms for determining fixed-pitch propeller parameters and some flight characteristics of a superlight aircraft at the early stage of designing are described.     

Global simulations using MHD codes: A few points to consider before you try one

A survey of all global time-dependent MHD simulations is presented. The survey includes a discussion of the physical situations simulated by the respective authors as well as the numerical algorithms employed. Finally a discussion of the advantages enjoyed by certain numerical schemes and the problems that a researcher will very likely encounter if he should undertake construction of such codes is presented.     

Nonlinear Adaptive Control of a Synchronous Machine

A nonlinear adaptive controller for a load-commutated brushless dc machine that allows the machine to develop high torque over a wide range of operating conditions, while satisfying voltage and current constraints on both stator and field circuits, is presented. The approach taken is fundamentally different from past work in that a nonlinear control is formulated from the steady-state model of the synchronous machine. Adaptive algorithms are presented for both the unknown load and motor cases.     

An empirical model of electron density for low and middle latitudes below 200 km

Our empirical model of electron density (n_e) for quiet and weakly disturbed geomagnetic conditions (Kp not greater 4) takes account of comparative analysis of existing models and of experimental data obtained by rockets and incoherent scatter radar. The model describes the n_e distribution in the 80 to 200 km height range at low and middle latitudes, and to some extent, in the subauroral region. It is presented in analytical form thus allowing one to calculate electron density profiles for any time. The electron density distribution at 140 km depends on the season (day of the year) and on the solar zenith angle. Profile variations during the day are for one season shown. Different from other models, ours specifies the variations during sunrise and sunset and reflects the particular profile shape at night admitting the occurrence of an intermediate layer.     

Soft X-ray characteristics of white dwarfs observed by EXOSAT

EXOSAT has observed 19 hot white dwarfs with alleged strong soft X-ray emission. Positive detection of a large fraction of this sample was obtained, among these practically all hot DA dwarfs. High-resolution spectral data, acquired with the 500 1/mm grating spectrometer, indicates no traces of He in the atmosphere of HZ43, i.e. n(He)/n(H) ? 10^?5 at a photospheric temperature of 60000 K (log g = 8). In contrast, the hot DA1 dwarf Feige 24 shows the presence of an appreciable He-abundance (n(He)/n(H) ? 10^?3); however no simple homogeneously mixed H/He atmosphere can explain the observed spectral shape.     

Dynamics of a spacecraft and normalization around Lagrangian points in the Neptune–Triton system

The problem of a spacecraft orbiting the Neptune–Triton system is presented. The new ingredients in this restricted three body problem are the Neptune oblateness and the high inclined and retrograde motion of Triton. First we present some interesting simulations showing the role played by the oblateness on a Neptune’s satellite, disturbed by Triton. We also give an extensive numerical exploration in the case when the spacecraft orbits Triton, considering Sun, Neptune and its planetary oblateness as disturbers. In the plane a × I (a = semi-major axis, I = inclination), we give a plot of the stable regions where the massless body can survive for thousand of years. Retrograde and direct orbits were considered and as usual, the region of stability is much more significant for the case of direct orbit of the spacecraft (Triton’s orbit is retrograde). Next we explore the dynamics in a vicinity of the Lagrangian points. The Birkhoff normalization is constructed around L₂, followed by its reduction to the center manifold. In this reduced dynamics, a convenient Poincaré section shows the interplay of the Lyapunov and halo periodic orbits, Lissajous and quasi-halo tori as well as the stable and unstable manifolds of the planar Lyapunov orbit. To show the effect of the oblateness, the planar Lyapunov family emanating from the Lagrangian points and three-dimensional halo orbits are obtained by the numerical continuation method.     

Circulation of energetic ions of terrestrial origin in the magnetosphere

Energetic ion composition measurements have now been performed from earth orbiting satellites for more than a decade. As early as 1972 we knew that energetic (keV) ions of terrestrial origin represented a non-negligible component of the storm time ring current. We have now assembled a significant body of knowledge concerning energetic ion composition throughout much of the earth's magnetosphere. We know that terrestrial ions are a common component of the hot equatorial magnetospheric plasma in the ring current and the plasma sheet out to ? 23 R_E. During periods of enhanced geomagnetic activity this component may become dominant. There is also clear evidence that the terrestrial component (specifically O⁺) is strongly dependent on solar cycle. Terrestrial ion source, transport, and acceleration regions have been identified in the polar auroral region, over the polar caps, in the magnetospheric boundary layers, and within the magnetotail lobes and plasma sheet boundary layer. Combining our present knowledge of these various magnetospheric ion populations, it is concluded that the primary terrestrial ion circulation pattern associated with enhanced geomagnetic activity involves direct injection from the auroral ion acceleration region into the plasma sheet boundary layer and central plasma sheet. The observed terrestrial component of the magnetospheric boundary layer and magnetotail lobes are inadequate to provide the required influx. They may, however, contribute significantly to the maintenence of the plasma sheet terrestrial ion population, particularly during periods of reduced geomagnetic activity. It is further concluded, on the basis of the relative energy distributions of H⁺ and O⁺ in the plasma sheet, that O⁺ probably contributes significantly to the ring current population at energies inaccessible to present ion composition instrumentation (? 30 keV).     

Interaction of Titan's atmosphere with Saturn's magnetosphere

The Voyager 1 measurements made during the Titan flyby reveal that Saturn's rotating magnetospheric plasma interacts directly with Titan's neutral atmosphere and ionosphere. This results from the lack of an intrinsic magnetic field at Titan. The interaction induces a magnetosphere which deflects the flowing plasma around Titan and forms a plasma wake downstream. Within the tail of the induced magnetosphere, ions of ionospheric origin flow away from Titan. Just outside Titan's magnetosphere, a substantial ion-exosphere forms from an extensive hydrogen-nitrogen exosphere. The exospheric ions are picked up and carried downstream into the wake by the plasma flowing around Titan. Mass loading produced by the addition of exospheric ions slows the wake plasma down considerably in the vicinity of the magnetopause.     

Mathematical description of the NaK model for MASTER-2005

The release of NaK droplets has been modeled for the new version of the European Meteoroid and Space Debris Terrestrial Environment Reference model MASTER-2005. Previously published versions of the model have been revised. The parameters of the model are introduced and discussed. NaK droplets consist of eutectic sodium–potassium alloy and have been released during RORSAT reactor core ejections. They contributed to the space debris environment in the centimeter and millimeter size regime. Sixteen nuclear powered RORSATs launched between 1980 and 1988 activated a reactor core ejection system in Sufficiently High Orbits (SHO), mostly between 900 and 950 km altitude. The core ejection caused an opening of the primary coolant circuit. The liquid coolant has been released into space during these core ejections. The outflow is considered as a discrete event for each of the sixteen core ejections in total. The NaK coolant has been forming droplets up to a diameter of 5.5 cm. NaK releases are restricted to a very narrow region near 65° inclination. This paper gives the parameters of the NaK release model as it is implemented in MASTER-2005. The quantitative values of all model parameters including characteristic diameter and uniformity parameter are presented. The ratio of the characteristic droplet size to the orifice diameter is discussed. It is estimated that altogether 128 kg of NaK-78 (8 kg per RORSAT) was released on orbit. Simulation runs show that there are still 45,000 droplets with a total mass of 97 kg in orbit at the reference epoch 1 May 2005, whereas the smallest droplet has a diameter of 5 mm. Results of orbit propagation simulation runs are presented in terms of spatial density.