共查询到20条相似文献,搜索用时 15 毫秒
1.
A simple technique for high-resolution imaging of distant objects is described and experimentally demonstrated. The technique, referred to as Fourier telescopy, is a variant of Fourier microscopy, which additionally uses phase closure for correction of intervening aberrations. It is an active-illumination technique that is scalable to angular resolutions of 1 nrad and to illuminators of extremely low power. A laboratory experiment demonstrates reconstruction of images of two simple objects with an angular resolution of 83 μrad. 相似文献
2.
Jacqueline Bertrand Pierre Bertrand Jean-Philippe Ovarlez 《International journal of imaging systems and technology》1994,5(1):39-51
This work concerns an extension of usual radar imaging in which the pictures of the target do not simply exhibit the position of elementary reflectors but also give the behavior of these reflectors when the frequency and the direction of illumination vary. Essentially, the technique consists of describing the target by a generalized image which can be computed from the knowledge of the backscattering function on a large domain in the angle-frequency space. A discussion of the physical relevance of the approach is given and its conclusions are used to derive a practical formulation relying on a special wavelet transform. The implementation of the technique is developed by using the fast Mellin transform. Special features of the method are the use of data in polar format without resampling and the fact that the computation can be easily parallelized.©1994 John Wiley & Sons Inc 相似文献
3.
现代雷达为获得较高的距离分辨力通常采用编码频率脉冲串信号和步进频率脉冲串信号,但都存在数据率低和较为严重的距离-多普勒耦合问题。在研究这两种信号特点的基础上,提出了调频编码脉冲信号形式并给出了相应的信号处理方法。经仿真对比可见,该信号形式及其处理方法能同时解决步进调频信号高距离-多普勒耦合、低数据率两大问题,具有较好的联合分辨力。 相似文献
4.
5.
Under the translational invariant (TI) configuration of stripmap imaging bistatic synthetic aperture radar (BISAR), the frequency domain expression of signal model is developed. Two forms, with an approximation of extracting the range dependence and an accurate iterative solution, as well as their respective focusing methods, that is the approximated solution method and the iterative solution method are presented here. The range-Doppler method is extended to the TI configuration of BISAR. Imaging simulation of the point targets and comparison with the bistatic backprojection method shows the feasibility of these methods as well as their merits and demerits. 相似文献
6.
7.
Three-dimensional imaging laser radar with a photon-counting avalanche photodiode array and microchip laser 总被引:4,自引:0,他引:4
Albota MA Heinrichs RM Kocher DG Fouche DG Player BE O'Brien ME Aull BF Zayhowski JJ Mooney J Willard BC Carlson RR 《Applied optics》2002,41(36):7671-7678
We have developed a threedimensional imaging laser radar featuring 3-cm range resolution and single-photon sensitivity. This prototype direct-detection laser radar employs compact, all-solid-state technology for the laser and detector array. The source is a Nd:YAG microchip laser that is diode pumped, passively Q-switched, and frequency doubled. The detector is a gated, passively quenched, two-dimensional array of silicon avalanche photodiodes operating in Geigermode. After describing the system in detail, we present a three-dimensional image, derive performance characteristics, and discuss our plans for future imaging three-dimensional laser radars. 相似文献
8.
Photon-counting compressive sensing laser radar for 3D imaging 总被引:2,自引:0,他引:2
We experimentally demonstrate a photon-counting, single-pixel, laser radar camera for 3D imaging where transverse spatial resolution is obtained through compressive sensing without scanning. We use this technique to image through partially obscuring objects, such as camouflage netting. Our implementation improves upon pixel-array based designs with a compact, resource-efficient design and highly scalable resolution. 相似文献
9.
A key issue in designing laser radar devices for short-range applications is the ability to estimate accurately the power seen by the receiver as a function of the measurement distance. To obtain a reasonable approximation of this power, the irradiance distribution over the sensor as well as the target surface, which is highly dependent on the type of the detector used, must be analyzed in detail. The calculation of signal power function by means of radiometry is discussed. A software package developed for simulating power transfer as a function of various optical parameters is presented. It can be applied to various types of laser sources, including high-power laser diodes (wide-stripe or stacked) and pigtailed laser diodes. 相似文献
10.
Measurements of signal amplitude distributions with a FM-cw CO2 laser radar have been made against various targets in both imaging and staring modes. Data show good agreement with theoretical distributions. From the measurements conclusions are drawn about the atmospheric- as well as target-induced effects. Beam wandering effects are shown to be of importance in the staring mode. 相似文献
11.
Reliability of signal processing technique for pavement damages detection and classification using ground penetrating radar 总被引:1,自引:0,他引:1
Ground penetrating radar (GPR) signal processing is a nondestructive technique, currently performed by many agencies involved in road management and particularly promising for soil characteristics interpretation. The focus of this paper is to assess the reliability of an optimal signal processing algorithm for pavement inspection. Preliminary detection and subsequent classification of pavement damages, based on an automatic GPR analysis, have been performed and experimentally validated. A threshold analysis of the error is carried out to detect possible damages and check if they can be predicted, while a second threshold analysis determines the nature of the damage. An optimum detection procedure is performed. It implements the classical Neyman-Pearson radar test. All the settings needed by the procedure have been estimated from training sets of experimental measures. The overall performance has been evaluated by looking at the usual receiver's operating characteristic. The results show that a reasonable performance has been achieved by exploiting the spatial correlation properties of the received signal, obtained from an appropriate analysis of GPR images. The proposed system shows that automatic evaluation of subgrade soil characteristics by GPR-based signal analysis and processing can be considered reliable in a number of experimental cases. 相似文献
12.
Lévêque-Fort S 《Applied optics》2001,40(7):1029-1036
An original acousto-optic method is described that allows one to reveal optical contrasts through biological tissues that are several centimeters thick with a millimeter-sized resolution. This technique is based on the interaction of scattered laser light with a focused ultrasonic field. The modulation depth of the optical speckle is related to local optical properties of the sample. Our parallel-processing approach to the demodulation of the speckle improves the observed degree of modulation by 2 orders of magnitude and quickly yields a good statistical value. Optically absorbing objects were imaged inside 35-mm-thick biological tissues. 相似文献
13.
Pham L. Tjhen W. Ye C. Polla D.L. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(4):552-555
Surface-micromachining techniques have been used in the fabrication of a 64×64 element PbTiO3 pyroelectric infrared imager. Polysilicon microbridges of 1.2 μm-thickness have been formed 0.8 μm above the surface of a silicon wafer. Each of the 4096 polysilicon microbridges measures 50×50 μm2 and forms a low thermal mass support for a 30×30 μm2 PbTiO3 pyroelectric capacitor with a thickness of 0.36 μm. The air-bridge formed reduces the thermal conduction path between the detector element and substrate. An NMOS preamplifier cell is located directly beneath each microbridge element. The measured blackbody voltage responsivity at 30 Hz is 1.2×104 V/W. The corresponding measured normalized detectivity (unamplified) D* is 2×108 cm-Hz1/2W at 30 Hz. The test chip fabricated measures 1×1 cm2 and contains more than ten thousand transistors and 4096 micromechanical structures with integrated ferroelectric microsensors. The technique of stacking of microsensors and integrated circuits represents a new approach for achieving high-density and high-performance integrated pyroelectric microsensors through minimization of circuit to sensor interconnection with extremely small thermal crosstalk 相似文献
14.
The effect of quantization noise arising in the course of digital processing of the signal of a laser Doppler anemometer on
the error in Doppler signal frequency estimation in the time domain is considered. It is shown that in high-precision measurements
the quantization noise that appears in amplitude quantization of the signal of a laser Doppler anemometer is comparable with
other noise sources and must be taken into account in estimation of the limiting accuracy of a laser Doppler anemometer. Results
of a simulation and experiment are presented.
Translated from Izmeritel'naya Tekhnika, No. 9, pp. 15–17, September. 1998. 相似文献
15.
Bartolini L De Dominicis L de Collibus MF Fornetti G Guarneri M Paglia E Poggi C Ricci R 《Applied optics》2005,44(33):7130-7135
We report the results of underwater imaging with an amplitude-modulated single-mode laser beam and miniaturized piezoactuator-based scanning system. The basic elements of the device are a diode laser source at 405 nm with digital amplitude modulation and a microscanning system realized with a small-aperture aspheric lens mounted on a pair of piezoelectric translators driven by sawtooth waveforms. The system has been designed to be a low-weight and rugged imaging device suitable to operate at medium range (approximately 10 m) in clear seawater as also demonstrated by computer simulation of layout performance. In the controlled laboratory conditions a submillimeter range accuracy has been obtained at a laser amplitude modulation frequency of 36.7 MHz. 相似文献
16.
Medina A Gayá F del Pozo F 《Journal of the Optical Society of America. A, Optics, image science, and vision》2006,23(4):800-805
A novel three-dimensional (3D) camera is capable of providing high-precision 3D images in real time. The camera uses a diode laser to illuminate the scene, a shuttered solid-state charge-coupled device (CCD) sensor, and a simple phase detection technique based on the sensor shutter. The amplitude of the reflected signal carries the luminance information, while the phase of the signal carries range information. The system output is coded as a video signal. This camera offers significant advantages over existing technology. The precision in range is dependent only on phase shift and laser power and theoretically is far superior to existing time-of-flight laser radar systems. Other advantages are reduced size and simplicity and compact and inexpensive construction. We built a prototype that produced high-resolution images in range the (z) and x-y. 相似文献
17.
The readout signal of a body dithered ring laser gyro contains both useful information and the dither component. The dither component must be removed to get the useful information. The dither stripping method can get the useful information without latency. But the quadrature demodulator only has 1/4 pulse resolution, which means that the quantization noise will limit the short-term accuracy. The effect and the property of quantization noise are analyzed in detail. Taking advantage of high-speed analog-to-digital conversion (ADC), the analog values of the two beat frequency signals in quadrature are sampled. A novel instantaneous phase method is introduced, which can get the residual phase besides 4× resolution and the quantization noise can be removed radically. The Allan variance analysis of experimental results shows that the quantization noise coefficient using this method is only 1/7 of that using the original 4× resolution method. 相似文献
18.
19.
Feasibility study of synthetic aperture infrared laser radar techniques for imaging of static and moving objects 总被引:4,自引:0,他引:4
Techniques for two types of 10-mum band synthetic aperture infrared laser radar using a hypothetical reference point target (RPT) are presented. One is for imaging static objects with a single two-dimensional scanning aperture. Through the simple manipulation of a reference wave phase, a desired image can be obtained merely by the two-dimensional Fourier transformation of the correlator output between the intermediate frequency signals of the reference and object waves. The other, with a one-dimensional aperture array, is for moving objects that pass across the array direction without attitude change. We performed imaging by using a two-dimensional RPT correlation method. We demonstrate the capability of these methods for imaging and evaluate the necessary conditions for signal-to-noise ratio and random phase errors in signal reception through numerical simulations in terms of feasibility. 相似文献
20.
A general theory for phase-resolved fingerprint imaging and background suppression based on laser-induced fluorescence is developed and presented in this paper. Novel approaches of incorporating an even-step phase shifting method with a homodyne-assisted phase-resolved method as well as the camera exposure control approach for the heterodyne-assisted phase-resolved method are proposed, theoretically formulated and discussed. Theoretical results imply that the fluorescence from latent fingerprints can be extracted effectively, irrespective of whether its lifetime is longer than that of the background or not. Furthermore, it is shown that there exists an optimum modulation frequency, which is dependent on the fluorescence lifetimes of both the background and the fingerprint, to obtain a fingerprint image with better contrast. 相似文献