运用Hough变换的搜索雷达检测和跟踪：第一部分：系统理论

本文的第一部分描述和分析了一种检测搜索雷达信号和数据的方法，该方法应用Ｈｏｕｇｈ变换的图象处理技术从多维数据图中提取目标信号和航迹，文中考虑了系统设计理论且给出了说明理论的模拟例子，同更传统的技术相比，该技术具有很多的优点。这些优点包括改进的检测，距离游动问题的一种解法，实现方法的灵活性，低扫描率等待时间的利用和不需要重新探测的自动跟踪截获。该理论与使用以前扫描所获初始信息来帮助发现目标的检测跟踪     

一种接近最优JPDA算法

多目标跟踪的关键问题是点迹－航迹数据关联。点迹是从能够提供位置信息的目标或背景杂波中接收到的信号。如果一条航迹关联上不正确的点迹，那么该航迹会偏离目标且过早终止。甚至会引起其它航迹也偏离目标，大多数点迹－航迹数据关联方法分为两类：多假设跟踪（ＭＨＴ）和联合概率数据关联（ＪＰＤＡ）。ＭＨＴ方法用所有或部分适宜的点迹修正航迹，并延迟判断那一个点迹是正确的。ＪＰＤＡ用合理点迹的加权和修正航迹，这些权值是     

一种隐蔽雷达扫描算法

当已知飞机前方地形路线，并具有关地段的数字高度地图时，地形跟随雷达发射的平均功率就可以大大减小。扫描图形可以很不规则，雷达天线也可以在更长的时间内保持隐蔽。这样，周期性地减少雷达发射可以极大地增强飞机在敌区的生存力。     

Martian CH(4): sources, flux, and detection

Recent observations have detected trace amounts of CH(4) heterogeneously distributed in the martian atmosphere, which indicated a subsurface CH(4) flux of ~2 x 10(5) to 2 x 10(9) cm(2) s(1). Four different origins for this CH(4) were considered: (1) volcanogenic; (2) sublimation of hydrate- rich ice; (3) diffusive transport through hydrate-saturated cryosphere; and (4) microbial CH(4) generation above the cryosphere. A diffusive flux model of the martian crust for He, H(2), and CH(4) was developed based upon measurements of deep fracture water samples from South Africa. This model distinguishes between abiogenic and microbial CH(4) sources based upon their isotopic composition, and couples microbial CH(4) production to H(2) generation by H(2)O radiolysis. For a He flux of approximately 10(5) cm(2) s(1) this model yields an abiogenic CH(4) flux and a microbial CH(4) flux of approximately 10(6) and approximately 10(9) cm(2) s(1), respectively. This flux will only reach the martian surface if CH(4) hydrate is saturated in the cryosphere; otherwise it will be captured within the cryosphere. The sublimation of a hydrate-rich cryosphere could generate the observed CH(4) flux, whereas microbial CH(4) production in a hypersaline environment above the hydrate stability zone only seems capable of supplying approximately 10(5) cm(2) s(1) of CH(4). The model predicts that He/H(2)/CH(4)/C(2)H(6) abundances and the C and H isotopic values of CH(4) and the C isotopic composition of C(2)H(6) could reveal the different sources. Cavity ring-down spectrometers represent the instrument type that would be most capable of performing the C and H measurements of CH(4) on near future rover missions and pinpointing the cause and source of the CH(4) emissions.     

Searching for liquid water in Europa by using surface observatories

Liquid water, as far as we know, is an indispensable ingredient of life. Therefore, locating reservoirs of liquid water in extraterrestrial bodies is a necessary prerequisite to searching for life. Recent geological and geophysical observations from the Galileo spacecraft, though not unambiguous, hint at the possibility of a subsurface ocean in the Jovian moon Europa. After summarizing present evidence for liquid water in Europa, we show that electromagnetic and seismic observations made from as few as two surface observatories comprising a magnetometer and a seismometer offer the best hope of unambiguous characterization of the three-dimensional structure of the ocean and the deeper interior of this icy moon. The observatories would also help us infer the composition of the icy crust and the ocean water.