Detectors for Multiomial Input

The binary detection problem is considered. Under an arbitrary noise environment, the input sample space can be transformed into a multinomial vector. Based on observations of this vector, the Neyman-Pearson optimal detector is developed for a known signal. When the signal strength is unknown, the likelihood ratio principle is followed to obtain consistent tests which use the Pearson's chisquare statistic. The resulting detectors are compared to others in terms of asymptotic relative efficiency under some actual noise distributions.     

Trimmed Generalized Sign and Modified Median Detectors for Multiple Target Situations

The trimmed generalized sign (TGS) nonparametric detector is introduced. The TGS and the modified median detector (MMD) are considered in situations when more than one target is present. Their performance is obtained through Monte Carlo simulations and compared with that of the generalized sign (GS) detector when detecting nonfluctuating signal in Gaussian noise.     

Signal-to-noise ratio and other characteristics of heterodyne radiation receivers

The theory of heterodyne radiation receivers for the infrared and far-infrared is reviewed. For simplicity, only systems based on photoemissive and photoconductive radiation mixers are considered. The signal-to-noise ratio is derived, and expressions for this quantity under various conditions are given. A brief comparison is made between heterodyne systems and high-resolution spectrometers using direct radiation detectors. It is concluded that for high spectral resolving powers and for relatively small astronomical sources, heterodyne systems are likely to offer a distinct advantage in signal-to-noise ratio, especially at long far-infrared wavelengths.     

Modified Savage and Modified Rank Squared Nonparametric Detectors

A modified form of the basic Savage statistic is considered and the performance of a modified Savage (MS) nonparametric detector using this modified statistic is derived. Also, a detector using a modified rank squared statistic (MRS) is introduced. The asymptotic relative efficiency (ARE) of the detectors is determined for chisquare, Rician, and log-normal signal fluctuations when the background noise is assumed Gaussian. The ARE performance of the generalized sign (GS) and Mann-Whitney (MW) detectors is also determined for these families of fluctuations. The ARE performance of the various detectors is then compared, and the results of a computer simulation are presented in which, for a finite number of samples, the performance of the modified detectors is compared with the performance of the GS and MW detectors. It is shown that when using a large number of reference noise samples, the ARE of the GS and MW detectors, the MRS and RS detectors, and the MS and Savage detectors are 0.75, 0.868, and 1, respectively. It is also shown that when using a finite number of reference noise samples the MS and MRS detectors can give a superior performance to that obtained with the MW detector, and that this is particularly true in the cases in which the degree of signal fluctuation is high.     

Optimization and Performance of Multilevel Quantization in Automatic Detectors

The optimization and performance of the double-threshold or binary method of automatic radar detection has been the subject of numerous studies in the past, and the loss due to this approximation has been shown to be 1 to 2-1/2 dB. By quantization of the input video into more than two levels, this loss can be avoided; however, little information is available on appropriate design procedures and expected performance. In this paper empirical procedures are described to find good settings of the first and second threshold levels, and the corresponding detection performance is determined. These results, which are believed to be close to optimum, show that for the case of quantization into four levels (2 bits), the loss in decibels is reduced to approximately 1/3 of the corresponding value for the binary case. In some cases this is equivalent to a saving of as much as 1-1/2 dB in signal-to-noise ratio.     

A novel bolometer for infrared and millimeter-wave astrophysics

We are developing a novel bolometer which uses a fine mesh to absorb radiation. The filling factor of the mesh is small, providing a small heat capacity and a low geometric cross-section to cosmic rays. The mesh is patterned from a free-standing silicon nitride membrane and is thermally isolated by long radial legs of silicon nitride. A thin metallic film evaporated on the mesh absorbs radiation by matching the surface impedance to that of free space. A neutron transmutation doped germanium thermistor attached to the center of the mesh detects the temperature increase from absorbed radiation. The low thermal conductivity and heat capacity of silicon nitride provide improved performance in low background applications. We discuss the theoretical limits of the performance of these devices. We have tested a device at 300 mK with an electricalNEP=4×10^–17 W Hz^–1/2 and a time constant =40 ms.     

Noise, Radar Moving-Window Detectors, and False Returns

Moving-window false report probability is shown to overestimate effects of noise. "False-report-start" probability is calculated and compared to the usual false report probability. The ratio of the two exceeds a simple function of window length, threshold, and noise probability, which is tabulated for some representative values.     

可压缩混合层中的大尺度结构及其作用初探

利用粒子示踪图像流动显示技术和粒子图像测速技术(PIV技术)研究了对流马赫数Mc=0.38时可压缩混合层发展早期出现的大尺度结构的形状和特性,并将这些混合现象与湍流脉动场结合起来研究了这些大尺度结构对流动混合效率的作用.将粒子示踪图像和湍流脉动强度场对比以后发现:混合层流动中早期出现的大尺度结构沿着顺时针方向旋转着向前移动;该结构上的流体微元具有高涡量.由于该结构旋转和高涡量产生了较大的诱导速度,加上该结构的非定常性导致在这些大尺度结构频繁出现的区域具有很高的脉动强度,从而可能带来较高的混合效率.     

Multiple hypothesis track confirmation for infrared surveillancesystems

An overall methodology is described for the application of a multiple hypothesis tracking (MHT) algorithm to the infrared (IR) surveillance system problem of establishing tracks on dim targets in a heavy clutter or false alarm background. The authors discuss the manner in which the detection and tracking systems are jointly designed to optimize performance. They present approximate methods that can conveniently be used for preliminary system design and performance prediction. They discuss the use of a detailed Monte Carlo simulation for final system evaluation and present results illustrating the proposed methods and comparing predicted and simulation performance     

The Detection Performance of the Siebert and Dicke-Fix CFAR Radar Detectors

The Siebert and the Dicke-fix CFAR radar detectors, used to maintain a constant false alarm rate (CFAR) in radar receivers under very similar circumstances, are considered. The Siebert detector represents the maximum-likelihood detection procedure for a signal in Gaussian noise of unknown power level, whereas the Dicke-fix makes use of a bandpass limiter to normalize the input and thus ensure a constant false alarm rate. The detection performance of the two detectors is determined and a comparison shows that over a wide range of parameters, the Dicke-fix introduces a loss which is approximately 1 B larger than for the Siebert detector.     

引射器混合室优化技术初步研究

混合室优化设计对超声速引射器引射性能的提高具有非常重要的作用。介绍了常温空气介质情况下引射器混合室不同设计参数试验件的数值模拟和实验研究结果;针对单喷嘴和多喷嘴引射器混合室收缩段长度、平直段长度及平直段截面直径等参数对引射器性能的影响作了对比分析。初步研究表明：多喷嘴引射器引射性能优于单喷嘴引射器,但多喷嘴引射器启动性能低于单喷嘴引射器;在引射器能正常启动的前提下,平直段直径越小,引射器性能更优;收缩段长度主要影响主、被动气流的混合效果,平直段长度主要影响引射器的启动性能,因此对混合室收缩段和平直段长度尺寸的设计需要根据引射器型式（单喷嘴或多喷嘴）合理确定。     

时间发展的二维混合层的物理分析和数值模拟

本文由四个部份组成.第一部份研究时间发展的二维剪切层流动的拓朴结构,提出了以下拓朴规律(1)沿零u线,流线的结点和鞍点是交替分布的;流线的鞍点和结点分别近似对应于压力值最大和最小的位置点;(2)压力值最大和最小的位置点是等压力线的中心点或鞍点;(3)如果在零u线上某点"0”,出现     

New criterion for aircraft susceptibility to infrared guided missiles

This paper assesses aircraft susceptibility from the first principles, with respect to the threat posed by passively guided infrared homing missiles; with an objective of gaining insight into the comprehensiveness of the relationship between aircraft susceptibility and aircraft infrared signature level. The conventional criterion of aircraft susceptibility assessment based on its lock-on envelop is found to be inadequate, and a new criterion termed here as the Lethal Envelop is presented. The proposed susceptibility assessment criterion is more relevant for coming generation of infrared-guided missiles, because of advancements in the infrared detection technology. A threshold infrared signature level is also proposed as benchmark to be satisfied by all infrared signature suppression systems; if aircraft susceptibility to infrared guided missiles is to be reduced. This analysis is vital for gauging the effectiveness of infrared signature suppression systems. A typical air-to-air combat situation is simulated, and the results that lead to aircraft susceptibility assessment are obtained from this model, which illustrates the comprehensiveness of the redefined aircraft susceptibility assessment approach.     

Background limited infrared and submillimeter instruments

The temperature and emissivity of infrared and submillimeter telescopes are basic parameters that drive the optical and thermal design of astronomical space projects. They determine also, among other parameters, the self-emission of the instrument and the photon noise produced by this radiation on the detectors. By comparing the telescope brightness with that of the sky in the 1m–1 cm wavelength range, general conditions for background limited photometry are derived. For <0.4 mm, temperature is the driving parameter, and for >0.4 mm, temperature and emissivity have equivalent importances. It can be shown on actual projects that these two regimes determine different optical and thermal concepts. Although based on a simplistic approach, this work intends to help designers to handle some basic system parameters of infrared and submillimeter instruments.     

Unmanned aircraft navigation for shipboard landing using infrared vision

This paper addresses the problem of determining the relative position and orientation of an unmanned air vehicle with respect to a ship using three visible points of known separation. The, images of the points are obtained from an onboard infrared camera. The paper develops a numerical solution to this problem. Both simulation and flight test results are presented.     

Comparison of Two Scanning Radar Detectors: The Moving Window and the Feedback Integrator

A comparison is made between the moving window and feedback integrator detectors for a scanning radar. Detection probabilities and position estimates are calculated by using a Monte Carlo simulation. The moving window is a slightly better detector than the feedback integrator: it provides 0.5-dB better detection capability and 8 percent more accurate estimate of position. However, the feedback integrator can be implemented more easily.     

Full-polarization matched-illumination for target detection and identification

This paper investigates the optimization of the full-polarization radar transmission waveform and the receiver response to maximize either target detection or identification performance. Application of such full-polarization matched-illumination techniques to simulated VHF-band frequency response data of mobile surface targets yields a significant performance improvement over that corresponding to chirped full-polarization transmission waveforms.     

The Voyager infrared spectroscopy and radiometry investigation

The infrared investigation on Voyager uses two interferometers covering the spectral ranges 60–600 cm^–1 (17–170 m) and 1000–7000 cm^–1 (1.4–10 m), and a radiometer covering the range 8000–25 000 cm^–1 (0.4–1.2 m). Two spectral resolutions (approximately 6.5 and 2.0 cm^–1) are available for each of the interferometers. In the middle of the thermal channel (far infrared interferometer) the noise level is equivalent to the signal from a target at 50 K; in the middle of the reflected sunlight channel (near infrared interferometer) the noise level is equivalent to the signal from an object of albedo 0.2 at the distance of Uranus.For planets and satellites with substantial atmospheres, the data will be used to investigate cloud and gas composition (including isotopic ratios), haze scale height, atmospheric vertical thermal structure, local and planetary circulation and dynamics, and planetary energy balance. For satellites with tenuous atmospheres, data will be gathered on surface and atmospheric composition, surface temperature and thermal properties, local and global phase functions, and surface structure. For Saturn's rings, the composition and radial structure, particle size and thermal characteristics will be investigated. Comparative studies of the planets and their satellite systems will be carried out.Paris Observatory.Cornell University.Jet Propulsion Laboratory.University of Maryland.