弹载聚束SAR平台的PFA算法

高分辨率SAR图像有助于导引头选择目标的关键部位进行精确打击,以扩大毁伤效果.尽管雷达平台在末制导阶段运动非常复杂,但由于天线始终指向目标,可以认为几何场景是聚束模式.而弹载平台的运动与机载平台不同,方位向和距离向都会作非匀速运动.非匀速运动不仅会引起越距离单元迁徙(MTRC),还会导致方位角非均匀变化,从而造成成像结果在距离向和方位向均出现散焦.本文通过对弹载聚束SAR几何场景和运动特点的分析,推导了变速条件下的PFA算法.首先研究了径向运动造成的越距离单元迁徙,并分析了运动补偿精度对成像质量的影响;然后采用SINC插值处理横向变速转动造成的方位角非均匀变化的问题.仿真实验获得良好聚焦的SAR图像,验证了本文方法的有效性.     

A superposed epoch study of the effects of solar wind stream interface events on the upper mesospheric and lower thermospheric temperature

The response of mesosphere and lower thermosphere (MLT) temperature to energetic particle precipitation over the Earth’s polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event-based study to be better observed. This work examines the influence of precipitation, triggered by solar wind stream interfaces (SI) event from 2002 to 2007, on polar MLT temperature. We first test the relationship between the ionospheric absorption measured by the SANAE IV (South African National Antarctic Expedition IV) riometer and the layer of energetic particle precipitation from POES (Polar Orbiting Environmental Satellites). The combined particle measurements from POES 15, 16, 17 and 18 were obtained close in time to the pass of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature retrieval. Here, a superposed epoch technique is described and implemented to obtain average temperature profiles during SI-triggered particle precipitation. The superposed epoch average shows no significant temperature decrease below 100 km prior to the onset of SI-triggered precipitation, whereas a clear superposed average temperature decrease is observed at 95 km after the SI impact. A case study of SI event also yields similar observations. Results indicate that cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream.     

Solar Wind Control of the Magnetospheric and Auroral Dynamics

A dependence of the polar cap magnetic flux on the interplanetary magnetic field and on the solar wind dynamic pressure is studied. The model calculations of the polar cap and auroral oval magnetic fluxes at the ionospheric level are presented. The obtained functions are based on the paraboloid magnetospheric model calculations. The scaling law for the polar cap diameter changing for different subsolar distances is demonstrated. Quiet conditions are used to compare theoretical results with the UV images of the Earth’s polar region obtained onboard the Polar and IMAGE spacecrafts. The model calculations enable finding not only the average polar cap magnetic flux but also the extreme values of the polar cap and auroral oval magnetic fluxes. These values can be attained in the course of the severe magnetic storm. Spectacular aurora often can be seen at midlatitude during severe magnetic storm. In particularly, the Bastille Day storm of July 15–16, 2000, was a severe magnetic storm when auroral displays were reported at midlatitudes. Enhancement of global magnetospheric current systems (ring current and tail current) and corresponding reconstruction of the magnetospheric structure is a reason for the equatorward displacement of the auroral zone. But at the start of the studied event the contracted polar cap and auroral oval were observed. In this case, the sudden solar wind pressure pulse was associated with a simultaneous northward IMF turning. Such IMF and solar wind pressure behavior is a cause of the observed aurora dynamics.     

用于速度测量的硬件相关仪

相关法测量速度已经发展了多年。由于相关运算计算量很大，软件实现时，对于大速度系统，受运算速度所限，其实时性及精度都不甚理想。为此，本文介绍１种用硬件实现相关运算的方法，并给出硬件相关仪结构及与８０９８单片机的接口框图。     

Study on solar sources and polar cap absorption events recorded in Antarctica

Particularly intense events occurred on the Sun in a period around minimum of solar activity during cycle 23. We investigated the characteristics of September 2005 and December 2006 events and the properties of the correlated observations of ionospheric absorption, obtained by a 30 MHz riometer installed at Mario Zucchelli Station (MZS-Antarctica), and of geomagnetic activity recorded at Scott Base (Antarctica). Solar events are studied using the characteristics of CMEs measured with SoHO/LASCO coronagraphs and the temporal evolution of solar energetic protons in different energy ranges measured by GOES 11 spacecraft.     

Use of varying shell heights derived from ionosonde data in calculating vertical total electron content (TEC) using GPS – New method

The dispersive nature of the ionosphere makes it possible to measure its total electron content (TEC). Thus Global Positioning System, which uses dual-frequency radio signals, is an ideal system to measure TEC. When data from an ionosonde situated in polar region was observed, the height of an approximated thin shell of electrons (shell height) used in GPS studies was seen not to be fixed but rather changing with time. Here we introduce a new method in which we included the varying shell heights derived from the ionosonde to map the slant total electron content from GPS to obtain a more precise vertical total electron content of the ionosphere contrary to some previous methods which used fixed shell heights. In this paper we also compared the ionosonde derived TEC with the GPS derived vertical TEC (vTEC) values. These GPS vTEC values were obtained from GPS slant TEC (sTEC) measurements using both fixed shell height and varying shell heights (from ionosonde measurements). For the polar regions, the varying shell height approach produced better results than the fixed shell height and compared to exponential function, Chapman function seems to be a better function to model the topside ionosphere.     

Solar particle precipitation into the polar atmosphere and their dependence on hemisphere and local time

The precipitation of solar energetic particles, protons as well as electrons, at high latitudes is commonly assumed to be homogeneous across both polar caps. Using Low-Earth Orbit POES (Polar Orbiting Environmental Satellites) we determine particle penetration ratios into the polar atmosphere for protons ranging from about 0.1 MeV to 500 MeV and for electrons spanning about one order of magnitude in energy with a maximum of 0.3 MeV. Based on power law fits for the POES spectrum we show, that for energies interesting for middle and lower atmosphere chemistry, particle flux over the poles is comparable in magnitude to flux at the geostationary orbit or at L1 in interplanetary space. The time period under study are the solar energetic particle (SEP) event series of October/November 2003 and January 2005.     

Quality Assessment of the IDS Contribution to ITRF2008

Doppler Orbitography Radiopositionning Integrated by Satellite (DORIS) is one of the four fundamental techniques contributing to the ITRF. The optimal coverage over the globe of the DORIS observing sites and sites co-located with GPS, allow a strong embedding of DORIS within the ITRF network. DORIS contributes to the access to ITRF through precise orbit determination of altimetric satellites with onboard DORIS receivers. The DORIS contribution to the ITRF2008 is enhanced by the fact that the solutions of seven analysis centers were included in the submitted combined time series of weekly station positions and daily polar motion. We evaluate the quality of the DORIS combined solution in terms of its agreement with the other techniques (VLBI, SLR, GPS) contributing to the ITRF2008 combination. We show in particular that the precisions of the current IDS products range between 1.5 to 2.6 mm for station positions (at the epochs of minimum variances); better than 1 mm/yr in velocities and between 170 and 260 micro-arc-seconds for polar motion, a significant improvement by a factor of three to five, compared to past data used in the ITRF2005 combination. This improvement is certainly due to improved analysis strategies employed by the seven IDS analysis centers that contributed to the combined weekly submitted solutions of station positions and polar motion. A spectral analysis of DORIS station height time series indicates that annual and semi-annual signals are dominant. However, TOPEX draconitic period of about 118 days is still detected in about 20% of the station position power spectra. DORIS height annual signals correlate well with GPS annual signal estimated at some co-located stations, which show that DORIS technique is able to detect loading signals.     

A statistical analysis of low frequency geomagnetic field pulsations at two Antarctic geomagnetic observatories in the polar cap region

The aim of this study is to investigate the characteristics of low frequency (∼0.5–5 mHz) geomagnetic field fluctuations as recorded at two Antarctic stations within the polar cap: the Italian observatory Mario Zucchelli Station (TNB) and the French–Italian observatory Dome C (DMC) in order to investigate the spatial extension and propagation characteristics of the phenomena observed at very high latitude. The stations have approximately the same geographic latitude, but a very different corrected geomagnetic latitude, being DMC close to the geomagnetic pole and TNB closer to the auroral oval.     

MY-9易碎材料在武器系统上的应用

介绍了MY-9易碎材料在武器系统上的成功应用。文中以实物和试验数据阐述了MY-9材料的易碎、密封、承压、耐侯和工艺等特性以及在研制导弹发射筒易碎盖和管路密封盖方面的经验。