The state of the art in D-region IRI modelling

While describing the formulation of IRI-79, in so far as it is applicable to the sub E-peak electron density profile, an attempt is made to compare its predictions with the available experimental evidence. The improvements needed for D-region electron density modelling are summarized. The current D-region IRI modelling effort is illustrated with a typical example.     

Berichtigung von druckfehlern

Ohne Zusammenfassung     

在服役中航空涡轮发动机的状态监控

本文是介绍涡轮发动机使用状态监控方面的一个新的综述.状态监控过程是使用各种不同的原理去跟踪发动机性能并找出机械故障模式的方法.本文也提出将监控资料转化为供航空公司使用的精确的维护建议需要的经验样本.     

Book reviews

Space Science Reviews -     

TeV gamma-rays from proton blazars

Proton acceleration in nearby blazars can be diagnosed measuring their intense TeV -ray emission. Flux predictions for 1101+384 (Mrk421) and 1219+285 (ON231), both strong EGRET sources (0.1 – 10 GeV), are obtained from model spectra of unsaturated synchrotron pair cascades fitted to publicly available multifrequency data. An experimen tal effort to confirm the predicted emission in the range 1–10 TeV would be of great importance for the problems of the origin of cosmic rays, the era of galaxy formation and the cosmological distance scale.     

Simulation study for the determination of the lunar gravity field from PRARE-L tracking onboard the German LEO mission

A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment – Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2–3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth–Moon system.     

Energy sources for the ionosphere—a survey

An outline is given of early aeronomical ideas about the formation of the ionosphere by solar wave radiation, and its development under the impetus of increasing basic knowledge. In particular, the development concerning solar radiation in the far ultraviolet and X-ray ranges is discussed (Sect. 1). General considerations on the relation with observable ionospheric parameters are given in Sect. 2 while the individual layers are discussed in Sect. 3. It is found that elder investigations, with wrong assumptions came to the right densities while their estimates of production rates were far too low. Since two years only satellite and laboratory data allow satisfying estimates.     

New description of the electron density profile

Methods are described by which the desired analytical representation of the whole profile might be reached while enforcing the most important observed physical features. An outline of future work in this connection is given.     

Feature enhancement and ATR performance using nonquadratic optimization-based SAR imaging

We present an evaluation of the impact of a recently proposed synthetic aperture radar (SAR) imaging technique on feature enhancement and automatic target recognition (ATR) performance. This image formation technique is based on nonquadratic optimization, and the images it produces appear to exhibit enhanced features. We quantify such feature enhancement through a number of criteria. The findings of our analysis indicate that the new feature-enhanced SAR image formation method provides images with higher resolution of scatterers, and better separability of different regions as compared with conventional SAR images. We also provide an ATR-based evaluation. We run recognition experiments using conventional and feature-enhanced SAR images of military targets, with three different classifiers. The first classifier is template based. The second classifier makes a decision through a likelihood test, based on Gaussian models for reflectivities. The third classifier is based on extracted locations of the dominant target scatterers. The experimental results demonstrate that the new feature-enhanced SAR imaging method can improve the recognition performance, especially in scenarios involving reduced data quality or quantity.     

Canada's role on space station

The paper addresses the evolution of the Canadian Space Station Program between 1981 and 2003. Discussions with potential international partners, aimed at jointly developing the current International Space Station program, were initiated by NASA in 1982. Canada chose, through the further development of the technologies of Canadarm on the space shuttle, to provide and operate an advanced and comprehensive external robotics system for space station, and to use the space station for scientific and commercial purposes. The program was to become a corner-stone of the new Canadian Space Agency. The development phase of the Canadian Space Station Program has been completed and two of the three major elements are currently operational in space.