2022测控技术与仪器专业英语阅读翻译.docx

2022测控技术与仪器专业英语阅读翻译篇一：测控技术与仪器专业英语课后阅读翻译(1,510) 第1章课后 Underwater Acoustic Signal In the operation of a sonar system the operator is repeatedly faced with the problem of detecting a signal which is obscured by noise. This signal may be an echo resulting from a transmitted signal over which the operator has some control, or it may have its origin in some external source. These two modes of operation arise in radar surveillance and in disciplines for techniques and for illustrations of the basic principles. Since there are many ways in which one can think about signal detection , it is desirable to define a term to denote special cases . The word detection will be used when the question to be answered is, ?Are one or more signals present? when the system is designed to provide an answered to this question , either deterministic or probabilistic, one speaks of hypothesis testing. The case of a single signal occurs so often that many system are designed to provide only two answers, ?Yes , a signal is present,? or ?No, there is no signal.? One can make the problem more complicated by endeavoring to classify the signal into categories. Decisions of this latter kind will be referred to as target classification. Normally a piece of detection equipment is designed to operate in a fixed mode and the parameters such as integrating time of rectifier circuits or persistence of the oscilloscope tube for visual detection cannot be changed readily. There will always be some uncertain signals, which the observer will be hesitant to reject or accept. In these cases the operator might have the feeling that if the integrating time of the detector or the persistence of the oscilloscope tube were longer, he could reach a decision about the existence of the signal. Wald(1950) has formulated this intuitive feeling into a theory of detection. When one is able to vary deliberately the interval over which one stores data in the reception system in order to achieve a certain level of certainty, one speaks of sequential detection. Frequently it is desirable to determine not only the presence or absence of the signal but also one or more parameters associated with the signal . The parameters of interest can vary widely from a simple quantity such as time of arrival or target bearing to the recovery of the completewaveform . When a system is designed to recover one or more parameters associated with thesignal , one speaks of signal extraction. The word signal was not defined and it was assumed that the reader had an intuitive felling for the word. Some elaboration may be in order since the definition of signal subjective and depends on theapplication . One may say that ?signal? is what one wants to observe and noise is anything that obscures the observation. Thus, a tuna fisherman who is searching the ocean with the aid of sonar equipment will be overjoyed with sounds that are impairing the performance of a nearby sonar system engaged in tracking a submarine. Quite literally, one man?s signal is another man?s noise. Signals come in all shapes and forms. In active sonar system one may use simple sinusoidal signals of fixed duration and modulations thereof. There are impulsive signals such as those made with explosions or thumpers. At the other extreme one may make use of pseudorandom signals. In passive systems, the signals whose detection is sought may be noise in the conventional meaning of the word; noise produced by propellers or underwater swimmers, for example. It should be evident that one of our problem will be the formulation of mathematical techniques that can be used to describe the signal. Although the source in an active sonar search system may be designed to transmit a signal known shape, there is no guarantee that the return signal whose detection is sought will be similar. In fact , there are many factors to change the signal. The amplitude loss associated with inverse spherical spreading is most unfortunate for the detection system nut it does not entail any distortion of the wave shape . (Incidentally, where the wave can be approximated locally as a plane wave.) The acoustic medium has an attenuation factor , which depends on the frequency . This produces a slight distortion of the wave shape and a corresponding change in the energy spectrum of the pulse. The major changes in the waveform result from acoustic boundaries and inhomogeneities in the medium. When echoes are produced by extended targets such as submarines, there are two distinct ways in which echo structure is affected. First, there is the interference between reflections from the different leads to a target strength that fluctuates rapidly with changes in the aspect. Secondly, there is the elongation of the composite echo due to the distribution of reflecting features along the submarines. This means that the duration of the composite echo is dependent in a simple manner on the aspect angle. If T is the duration of the echo from a point scatterer, and L is the length of the submarine, the duration of the returned echo will be T=(2L/c)cosA ,where A is the acute angle between the major axis of the submarine and the line joining the source and the submarine. C is the velocity of sound in the water. Of course, LcosA must be replaced by the beam width of the submarine when A is near. A final source of pulse distortion is the Doppler shifts produced by the relative motions between the source, and the target (or detector in passive listening) may each have a different velocity relative to the bottom, the variety of effects may be quite large. 水下声波信号 在声纳操作过程中，操作员经常需要对受噪声干扰的信号进行检波。干扰信号可能来自操作员发出信号的反射波或者外部声源的信号。这两种类型的干扰对主动声纳和被动声纳都会造成很大影响。类似的情况在雷达监测、工程类和图像类专业的基本原理都会涉及到。 当你想到信号检测时有多种方法，那么定义一个术语来表示特殊情况便是可行的。当问题的答案是“当前有一个还是一个多个信号？”时，检波一词将被使用。一个系统被设计来为这种问题提供答案-无论是必然性还是偶然性，这就需要谈及假设检验；当一个信号反复出现的情况下，许多系统只被设计提供两个答案：“是的，当前有一个信号”或“不，当前没有信号”。力图将信号分类会使问题复杂化，因为后者的结论将涉及到目标分类。 一般来说，一种检波仪器只被设计在固定的类型和参数下工作，不容易被改变，例如时间积分检波电路和光学检测的辉光示波管。当出现不明信号时，观察者在拒绝或接收信号方面有所迟疑。在这种情况下，操作员会有种感觉如果检波电路或者示波管能够延长时间那么他就能下结论该信号是否存在。沃尔德（1950）在他的检波理论系统阐述了这种直觉。如果（一个检测检测方法）能够主动去改变时间间隔并在接收系统里储存数据以便达到确定的某一水平，这就是顺序检测。 一般不仅能够确定信号存在与否，而且还能确定一个或多个与信号关联的参数。在还原完整波形时我们所感兴趣的参数在各简单分量间有很大差别，例如信号的到达时间和相位。 当一个系统被设计来提取一个或多个信号参数时，这就是信号抽取。 信号一词并没有明确的定义，只是在读者对它有直观了解时的一种假设。有些较为详细的解释为了对信号一词进定义可能导致是比较主观的或者狭隘与所应用的条件。也许你会说信号就是你想观察到的而噪声就是对观察者产生干扰的信号。但是，一个渔民在用声纳设备搜索海洋时，附近用来追踪潜艇的声纳干扰导致的信号削减常常会使他欣喜若狂。毫不夸张地说，一个人的信号将会是另一个人的噪声。 信号的形式和构成是多种多样的。在主动声纳系统中，可以利用相关的固定宽度和调制正弦信号。类似的有脉冲信号，例如爆炸或者撞击。在一些极端的情况可以利用伪随机信号。在被动声纳系统中，例如螺旋桨或潜泳者发出的噪声。很明显，如何利用数学公式的方法来描述一个信号成为了我们所面临的问题。 即是在主动声纳系统中的超声波发射器传播已知波形的信号，但无法保证检测后查找出来的反射信号也是类似的波形。振幅和反向球面传播信号失去关联是检波系统最不利的情况，因为它无法承担任何波形畸变。（偶然地，这种事件的乐观情况并不适用于2维波，除非它传播到足够远的地方，可以近似认为是平面波。）声波的传导介质会对其造成衰减，（衰减的程度）取决于声波的频率。这就造成了少量的波形失真和对脉冲波形能谱造成相当的改变。主要的改变还是由于波形的边缘效应和传播介质的不均匀所引起的。 当反射波是由外部物体例如潜艇所发出的，这时反射波的结构主要受两种不同方式的影响，第一，由两种反射信号之间的干扰导致外界声源的强度与跟随相位的改变迅速波动，第二，合成反射波的延伸是沿着（来自）潜艇反射的散布特征，这就意味着持续时间取决于相位角的简单特征。如果T是反射波由一个点扩散的持续时间，L是潜艇的长度，那么反射波的回射时 间就是 ， 是潜艇主轴和声纳拖曳线之间的夹角（锐角），C则是声音在水中的传播速率。当然，当 接近的时候 必须用潜艇的宽度代入。 最后一个造成脉冲波形失真的原因声源，船体，介质，目标之间相对运动所造成的多普勒效应。由于声源，介质，目标（或者被动接收器的探测端）相对于船体都有不通的速度向量，所以各种因素的影响之间的区别也很大。 第五章课后 A random erroris due to acontrolled， large number of independent small effects that cannothe identified orit is a statistical quantity. As such，iteach replication of the observations. If a large number of readings is will vary for the same quantity.the scatter of the data about a mean value can be evaluated. The scatter generally follows a guassian distribution about a mean value.which is assumed to be the true value. Accuracy is the deviation of the output from the calibration input or the true value. If the accuracy of a voltmeter is 2% full scale as described in the preceding section·the maximum deviation i、士2units for all readings. 一个随机误差是由于控制,大量的独立影响小,不能他发现或 这是一个统计量。因此,它每个复制的观察。如果大量的读数是 同样数量的不同而不同。散射的数据值可以评估。散高斯分布通常遵循关于意味着value.which被认为是真正的价值。准确性是偏差的输出的输入或真正的校准价值。如果把电压表的准确性2%全面描述在前面的 部分·最大偏差我,士2units所有阅读资料。 第五章.Noncontact Temperature Measurement Any object at any temperature above absolute zero radiates energy. This radiationvaries both in intensity and in spectral distribution with temperature.Hence.temperature may be deduced by measuring either the intensity or the spectrum of theradiation. The total energy density radiating from an ideal?blackbody?(more on that later) isgiven by the Stefan-boltzmann law·E=6T'·where E is energy density in W/cmz.6 Isthe Stefan-boltzmann constant(5. 6697 X 10 'z W/cmz K?)and T is the absolutetemperature(K).In other words·the total radiated energy is proportional to the fourthpower of the absolute temperature. A11 objects.particularly ideal blackbody objects.also absorb incident radiation. (Uiven time to equilibrate.and presuming they are insulated from the heating or cooling effects of surrounding air or other materials.they will eventually reach a point where they absorb and radiate energy at equal rates. ()ne consequence of this is that if an object (a temperature sensor.for example) is an ideal blackbody.is perfectly insulated.and is flooded on its entire surface with radiation from a radiating source.it will eventually reach an equilibrium sources and blackbody calibration sources are available).the temperature of the sensor is a measure of the temperature of the radiating object. 任何物体在任何温度高于绝对零度的辐射能量。这种辐射无论是在不同强度和在光谱分布和温度。因此。通过测量温度可以推导出要么强度或频谱的辐射。总能量密度辐射从理想'blackbody”(稍后详细介绍) 鉴于法律的Stefan-boltzmann·E = 6 T '·E在是能量密度在W / cmz。 6Stefan-boltzmann的常数(5。 6697 X 10 ' z W / cmz K”)和T是绝对的温度(K)。换句话说·总辐射能量是成正比的第四 绝对温度的力量。A11对象。特别是理想黑体对象。也会吸收入射辐射。(Uiven时间一致。和他们隔绝放肆的加热或冷却周围空气的影响或其他材料。他们最终会达到一个临界点他们吸收和辐射能量在相同的利率。()东北的后果是,如果一个对象(一个温度传感器。例如)是一种理想的黑体。是完全绝缘。和是在整个表面淹没与辐射发射源。它最终将达到平衡本文来源：网络收集与整理，如有侵权，请联系作者删除，谢谢！第14页 共14页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页第 14 页 共 14 页