PMHT: problems and some solutions

The probabilistic multihypothesis tracker (PMHT) is a target tracking algorithm of considerable theoretical elegance. In practice, its performance turns out to be at best similar to that of the probabilistic data association filter (PDAF); and since the implementation of the PDAF is less intense numerically the PMHT has been having a hard time finding acceptance. The PMHT's problems of nonadaptivity, narcissism, and over-hospitality to clutter are elicited in this work. The PMHT's main selling-point is its flexible and easily modifiable model, which we use to develop the "homothetic" PMHT; maneuver-based PMHTs, including those with separate and joint homothetic measurement models; a modified PMHT whose measurement/target association model is more similar to that of the PDAF; and PMHTs with eccentric and/or estimated measurement models. Ideally, "bottom line" would be a version of the PMHT with clear advantages over existing trackers. If the goal is of an accurate (in terms of mean square error (MSE)) track, then there are a number of versions for which this is available.     

Integrated track maintenance for the PMHT via the hysteresis model

Unlike other tracking algorithms the probabilistic multi-hypothesis tracker (PMHT) assumes that the true source of each measurement is an independent realisation of a random process. Given knowledge of the prior probability of this assignment variable, data association is performed independently for each measurement. When the assignment prior is unknown, it can be estimated provided that it is either time independent, or fixed over the batch. This paper presents a new extension of the PMHT, which incorporates a randomly evolving Bayesian hyperparameter for the assignment process. This extension is referred to as the PMHT with hysteresis. The state of the hyperparameter reflects each model's contribution to the mixture, and thus can be used to quantify the significance of mixture components. The paper demonstrates how this can be used as a method for automated track maintenance in clutter. The performance benefit gained over the standard PMHT is demonstrated using simulations and real sensor data     

The Formation Of The First Stars In The Universe

In this review, I survey our current understanding of how the very first stars in the universe formed, with a focus on three main areas of interest: the formation of the first protogalaxies and the cooling of gas within them, the nature and extent of fragmentation within the cool gas, and the physics – in particular the interplay between protostellar accretion and protostellar feedback – that serves to determine the final stellar mass. In each of these areas, I have attempted to show how our thinking has developed over recent years, aided in large part by the increasing ease with which we can now perform detailed numerical simulations of primordial star formation. I have also tried to indicate the areas where our understanding remains incomplete, and to identify some of the most important unsolved problems.     

美国西南航适航指令事件始末

在2007年3月,美国西南航空公司(SWA)发现自己所运营的飞机不符合适航指令(AD)后将这一问题通过自愿报告系统(VDRP)向其审定管理叻公室(CMO)进行汇报,并采取补救措施.与此同时,SWA有46架与AD不符的波音737飞机又继续运营了9天.SWA的主管称其误以为CMO准许其继续运营.     

树上的小王子

每个人心里都长着一棵树,上面住着只属于自己的小王子。其实没有预料到,这会是一本这么有意思的小书。它是一个跟爱情有关的童话,一个治愈系的成长故事,更是一次照见内心童真自我的发现之旅。故事里最有趣的,当然还是那个帮人做梦的鹿头上。他能帮人重温旧日的好时光,再见念念不忘的那个人,或是得到一直想要却未必能在现实里得到的东西……听起来,他真的很像小王子,来自另一个奇幻美妙的世界。那里只有单纯与快乐,而他柔软干净,能为这个纷乱世界的人带来温暖与慰藉。而且,即使只是帮人做一场梦,     

阅尽千番赏更真

当外滩三号渐渐走近了人们的生活,当那种独特的设计和经营模式成为了一种时尚,李景汉意识到,是时候走向自己的下一站了。外滩三号迅速掀起时尚潮流的经历,让他意识到了选址对艺术推广的重要性,要让尽可能多的人加入艺术欣赏的行列,要感染到尽可能多的人,就一定要把艺术空间建在大都市的中心。如果说外滩是上海的中     

天气对航班飞行的影响

在飞机起飞、降落和空中飞行的各个阶段都会受到气象条件的影响,风、气温、气压都是影响飞行的重要气象要素地面风会直接影响飞机的操纵,高空风会影响飞机在航线上的飞行速度和加油量气温高低,可改变发动机的推力、影响空速表、起落滑跑距离等等气温高于标准大气温度时,会增加飞机起飞滑跑距离和上升爬高时间,降低飞机载重量气压会影响飞机的飞行高度由于各地气压经常变化,往往造成气压高度表指示的误差。此外,雷暴、低云、低能见度、低空风切变、大气湍流、空中急流、颠簸、结冰等天气现象都直接威胁飞行安全。     

德国的歌剧魅力

德国古典音乐所留下的遗产是无与伦比的。路德维希·凡·贝多芬(Ludwig van Beethoven)、约翰·塞巴斯迪安·巴赫(Johann Sebastian Bach)、罗伯特·舒曼(Robert Schumann)、费利克斯·门德尔松(Felix Mendelssohn)、约翰内斯·勃拉姆斯(Johannes Brahms)以及里夏德·瓦格纳(Richard Wagner)……之所以会产生如此众多声名显赫的音乐家,源于这个民族对音乐的喜爱。同样,在德国旅行也就少不了去看看那些歌剧院,欣赏一下歌剧和古典音乐。     

天气对航班飞行的影响

飞机是一种现代化的交通运输工具,它给人们旅行带来很大的方便,人们都希望所乘坐的民航班机能够安全、舒适、正点地抵达目的地。但您有时也会遇到因飞机返航、备降或暂缓起飞而使航班延误的情况。可您是否知道,尽管现在飞机性能不断提高,地面保障设备不断改善,但是天气因素仍然对飞行安全、正点和经济效益有着严重的影响。     

Exploring The Saturn System In The Thermal Infrared: The Composite Infrared Spectrometer

The Composite Infrared Spectrometer (CIRS) is a remote-sensing Fourier Transform Spectrometer (FTS) on the Cassini orbiter that measures thermal radiation over two decades in wavenumber, from 10 to 1400 cm^{− 1} (1 mm to 7μ m), with a spectral resolution that can be set from 0.5 to 15.5 cm^{− 1}. The far infrared portion of the spectrum (10–600 cm^{− 1}) is measured with a polarizing interferometer having thermopile detectors with a common 4-mrad field of view (FOV). The middle infrared portion is measured with a traditional Michelson interferometer having two focal planes (600–1100 cm^{− 1}, 1100–1400 cm^{− 1}). Each focal plane is composed of a 1× 10 array of HgCdTe detectors, each detector having a 0.3-mrad FOV. CIRS observations will provide three-dimensional maps of temperature, gas composition, and aerosols/condensates of the atmospheres of Titan and Saturn with good vertical and horizontal resolution, from deep in their tropospheres to high in their mesospheres. CIRS’s ability to observe atmospheres in the limb-viewing mode (in addition to nadir) offers the opportunity to provide accurate and highly resolved vertical profiles of these atmospheric variables. The ability to observe with high-spectral resolution should facilitate the identification of new constituents. CIRS will also map the thermal and compositional properties of the surfaces of Saturn’s icy satellites. It will similarly map Saturn’s rings, characterizing their dynamical and spatial structure and constraining theories of their formation and evolution. The combination of broad spectral range, programmable spectral resolution, the small detector fields of view, and an orbiting spacecraft platform will allow CIRS to observe the Saturnian system in the thermal infrared at a level of detail not previously achieved.This revised version was published online in July 2005 with a corrected cover date.     

ATR.The people.The planes.The total service system.

Aces,Colombia/Air Atlantique,France/Air Botswa-na,Botswana/Air Calédonie,France/Air(?),Austria/Air Dolomiti,Italy/Air Gabon,Gabon/AirGreece,Greece/Air Sicilia,Italy/Air Guadeloupe,     

穿着五十度灰

<正>你是一个电影迷吗?改编自小说《格雷的五十道阴影》(Fifty Shades of Grey)的电影《五十度灰》可谓今年最卖座的电影之一。这部投资仅4000万的电影席卷了全球近5亿的票房。追究其原因,有人将之归功于影片特殊的题材与卖点,但不可否认,无数人观影过后印象最深的便是男主角格雷先生非凡的气质与极具品味的绅士装扮。他从服装配饰到生活用品,代步工具从顶级座驾到私人专机,还有景     

后疫情时代航空维修产业发展趋势有关思考

1航空维修产业概述 航空维修是指对飞机及其上的技术装备进行的维护和修理,确保飞机的安全适航,因此航空维修是飞机使用的前提和必要条件,是航空业的重要组成部分.根据维修对象的不同,航空维修一般可分为航线维护、机体维修、发动机维修、起落架及其他机载设备维修等.