Numerical simulation of subsurface radar for detecting buried pipes

A subsurface radar for the detection of dielectric or metal pipes buried in the ground is investigated numerically. The two dimensional transmission line matrix method was used to obtain images of buried pipes illuminated by electromagnetic pulses generated by a ground-penetrating radar. The present study is only applicable for two-dimensional cases as it assumes infinitely long pipes and sources. However, the technique may be used for three-dimensional cases as long as the antenna is parallel to the underground pipes and is not near the ends or the bends of the pipes. For the cases shown, 480 grid points in the x direction and 220 in the γ direction were used. The required memory to run the simulation software was 1.1 Mb. With 6000 iterations, the total CPU time for the case was 218 s on a MicroVax II workstation     

Advanced polarimetric subsurface FM-CW radar

The subsurface radar suffers from two typical problems, i.e., strong clutter from surface and severe wave attenuation in the underground. This paper presents a unique countermeasure to these problems using a polarimetric FM-CW radar and an equivalent sensitivity time control (STC) technique. The authors apply the polarimetric filtering principle to suppress surface clutter either in the Co-pol channel or in the X-pol channel of synthetic aperture radar, yielding to polarimetric enhanced target image. This technique works when the surface clutter and target have different polarization properties. Moreover, they use an equivalent STC technique specially suited for FM-CW radar for a deep object sounding to compensate wave attenuation within the ground. These techniques contribute to a significant improvement of the radar performance and the detection image contrast, although the detection of the target is in general a much more complicated topic. The field experiments were carried out to show the usefulness of the method. Some detection results are presented     

A novel 3-D subsurface radar imaging technique

The problem of the formation of subsurface images using stand-off forward looking radar is by far more severe than that of forming the radar images in the free-space. A subsurface image needs to be accurately focused taking into account both the refraction and dispersion of the wavefield. This paper presents a novel imaging algorithm specially tailored for subsurface sensing. A simple and effective characterization technique for the retrieval of the dielectric permittivity is outlined. The proposed soil characterization and subsurface imaging techniques are validated experimentally. Results show that the geometric distortion in the subsurface images due to the refraction and dispersion of the wavefields is successfully corrected     

A wavefront reconstruction method for 3-d cylindrical subsurface radar imaging

In recent years, the use of radar technology has been proposed in a wide range of subsurface imaging applications. Traditionally, linear scan trajectories are used to acquire data in most subsurface radar applications. However, novel applications, such as breast microwave imaging and wood inspection, require the use of nonlinear scan trajectories in order to adjust to the geometry of the scanned area. This paper proposes a novel reconstruction algorithm for subsurface radar data acquired along cylindrical scan trajectories. The spectrum of the collected data is processed in order to locate the spatial origin of the target reflections and remove the spreading of the target reflections which results from the different signal travel times along the scan trajectory. The proposed algorithm was successfully tested using experimental data collected from phantoms that mimic high contrast subsurface radar scenarios, yielding promising results. Practical considerations such as spatial resolution and sampling constraints are discussed and illustrated as well.     

Developing experimental models for a bistatic subsurface radar

The letter presents preliminary results from a recent experimental investigation to characterise the electromagnetic scattering from conducting objects submerged in a dissipative half-space. The variation of the magnetic field with respect to the depth of the scattering object is discussed. Correlations are also sought between the measured field components and the size of the scattering object.     

Advanced cooling system using miniature heat pipes in mobile PC

This paper describes various cooling solutions using heat pipes for cooling a notebook PC. These are: 1) heat pipe with heat spreader plate; 2) hybrid system-i.e., heat pipe with heat sink and fan; and 3) hinged heat pipe system. For heat input of less than 12 W, the thermal resistance measured between the surface of the CPU to ambient was obtained as follows: greater than 8°C/W for system 1) and 4-6°C/W for systems 2) and 3). For the CPU having specification of surface temperature of 95°C and 40°C ambient, then system 1) can be dissipated by about 6 W, whereas systems 2) and 3) can handle 13 W. Experimental results of these three systems are included and discussed in this paper     

A characterization of subsurface radar targets

The capability of subsurface target identification at shallow depths has been demonstrated using an electromagnetic video or base-band pulse radar. Real radar measurements were collected for five targets at a depth of 5 cm (2 in) in various ground conditions. These measurements were processed for target characterization and identification. Identification performance based on a single radar observation was evalualted. The identification process requires only simple algebraic operations and thus offers the potential of real-time on-location identification of subsurface targets.     

A system model and inversion for synthetic aperture radar imaging

A system model and its corresponding inversion for synthetic aperture radar (SAR) imaging are presented. The system model incorporates the spherical nature of a radar's radiation pattern at far field. The inverse method based on this model performs a spatial Fourier transform (Doppler processing) on the recorded signals with respect to the available coordinates of a translational radar (SAR) or target (inverse SAR). It is shown that the transformed data provide samples of the spatial Fourier transform of the target's reflectivity function. The inverse method can be modified to incorporate deviations of the radar's motion from its prescribed straight line path. The effects of finite aperture on resolution, reconstruction, and sampling constraints for the imaging problem are discussed.     

SAR processing of ground-penetrating radar data for buried UXOdetection: results from a surface-based system

Battelle and The Ohio State University ElectroScience Laboratory have built and demonstrated a ground-penetrating radar (GPR) system for locating buried unexploded ordnance (UXO), the system is ground based and towed by an autonomously controlled vehicle as part of the subsurface ordnance characterization system (SOCS). This paper presents the results of the synthetic aperture radar (SAR) processing of the radar data acquired at Tyndall Air Force Base, FL, and Jefferson Proving Ground (JPG), IN     

星球次表层探测雷达回波仿真

在中国未来的深空探测计划中,将采用天基雷达探测技术,以实现对整个星球表面次表层结构的探测。星载高频雷达探测仪通过月球表面天底点和次表面天底点的回波时延差与强度探测月球分层结构。为了获取次表层结构信息,研究了电磁波在月球分层结构内散射与传播的建模与模拟,对利用KA近似方法计算表层及次表层回波的方法进行了研究,分析了不同参数对回波的影响,最后通过仿真进行了验证。     

基于成像激光雷达的地形辅助导航研究

成像激光雷达通过扫描可以测量高精度的地形数据,基于成像激光雷达的地形辅助导航系统是纠正惯导误差的有效手段.根据激光雷达测距模型提出了基于成像激光雷达的地形辅助导航系统,将激光雷达看作一个多维距离传感器阵列,利用卡尔曼滤波器迭代估计系统的状态误差,从而纠正惯导累积误差.根据激光雷达测距关系推导了系统的扩展卡尔曼滤波方程,并对成像激光雷达多维测量数据采用最小均方误差准则进行融合,融合滤波器组合了多个测量数据的信息,有效克服了测量噪声和数据丢失对单个滤波器的影响,从而提高了导航性能.然后利用局部可观测性对系统的性能进行了分析,并对提出的算法作了大量的仿真实验进行验证.     

基于激光成像雷达制导系统的仿真设计

介绍了激光成像雷达应用于制导系统中的优势,提出应用仿真技术辅助外差式激光成像雷达制导系统设计的方法。分析了激光成像雷达制导仿真系统的四个主要组成部分：光学部分、数据处理部分、通用库部分和稳定跟踪部分。结合不同环境、器件性能对系统的影响,具体分析各部分的模块并给出多种数学建模方案。最后指出该系统需要进一步完善的功能。     

DPL固体激光成像雷达系统研究

介绍了DPL固体激光成像雷达的工作原理、系统组成,系统以高重频DPL固体激光器为光源,雪崩探测器直接探测体制,二维光机扫描成像,距离伪彩色3D成像方式,可以快速获取数千米远物体的三维图像.分析了大气衰减对作用距离的影响.该系统可用于目标侦察、地形测量、障碍物探测等应用领域.     

An efficient FPGA-based implementation of UWB radar system for through-wall imaging

The work presented in this paper aims to develop a low-cost ultra-wideband (UWB) radar system that has the capability to image through the wall of a human target. The proposed radar system relies heavily on a field-programmable gate array (FPGA) platform. The Xilinx FPGA Kintex-7 (KC705) board is employed to integrate the main functionalities of the radar system, such as the generation and acquisition of a UWB signal. The generated signal is a monocycle signal, which has an ultra-wide bandwidth. Due to the UWB nature of this signal, the radar system achieves better penetration ability, as well as high imaging resolution. However, the major challenge of a UWB radar system lies in the stage of digitization, as it requires a high sampling rate analog-to-digital converter (ADC). In fact, such a chip is very expensive. Hence, to reach a high sampling resolution using a low-cost and low-speed ADC, an efficient sampling strategy is implemented. In contrast to other UWB sampling methods, which require a hardware delay line chip, the new sampling scheme depends only on the FPGA firmware to realize a combination of real-time and equivalent-time sampling, which provides better jitter performance. Finally, to demonstrate the imaging capability, experimental tests are conducted in an indoor environment while human targets are located in different places. The measurement results revealed that the proposed radar system has the ability to provide 2D images that accurately determine the location of the target.     

New mechanism for subsurface imaging in silicon

We report the use of photothermal radiometric microscopy to image through silicon wafers. Experimental results are presented which show that the signal obtained decreases as the normal emissivity of the material on the back surface increases. The theory for the emissivity of partially transparent objects has been extended to explain these findings. We conclude that the contrast is due to photon-induced switching of the infra-red transmission coefficient of the silicon.     

太赫兹近场成像雷达系统误差补偿方法

太赫兹成像雷达具有合成孔径时间短、分辨力高的优点,适用于近场探测,但由于器件成熟度相对不高,雷达系统常存在较大的系统失真,会降低信号质量;同时,系统固有延时的存在会引起距离测量误差,二者均会恶化雷达成像的质量。针对系统失真和固有延时,提出了最小二乘法估计的幅相误差补偿方法和固有延时补偿方法,并给出了系统误差的测量方法。试验测试结果表明,用该方法对系统进行补偿后能有效提高图像空间分辨力,改善图像质量。     

Microwave holographic subtraction for imaging of buried objects

A simple technique for subtracting microwave holograms is presented. The technique is novel in that it superimposes a hologram over the complement of a second one obtained through an inverting amplifier with unity gain. Since the holograms contain mainly the wavefront information, only the difference of two dissimilar microwave fields is recorded. The technique is demonstrated by subtracting the effect of the front-surface reflections from the hologram of an object concealed behind a box of dry sand to retrieve the image of the object itself. This technique can have many applications, like in imaging of buried objects in dielectrics.     

A system for on line imaging of scattering centers on rotating radar targets

A simple measurement and data processing system is presented which, at the output, on a television screen, continuously and on line yields a one-dimensional radar image of rotating targets together with the corresponding two-dimensional optical image. The system makes use of the well-known fact that the fine structure in the instantaneous Doppler spectrum of the radar echo from a rotating target yields high cross range resolution of the scattering centers. It is very useful for the analysis of the scattering center distribution on complicated targets, for on line evaluation of the effect of comouflaging and for related areas as glint analysis and RCS prediction, for example.     

Space-based radar systems intended for subsurface sounding of Mars and Moon soils

Space-based radar systems intended for investigating the subsurface layers of Mars, Phobos, and Moon are discussed. The characteristics of domestic radar systems developed in preparing the space projects devoted to the study of Mars soils (Mars-96 mission), Phobos ground (Phobos 1 and 2 and Phobos-Grunt missions), and the Moon surface (Luna-Glob mission) are presented. The characteristics of a long-wave Mars advanced radar for subsurface and ionosphere sounding (MARSIS) (Mars Express project) and a long-wave shallow radar (ShaRad) system included in Mars Reconnaissance Orbiter, as well as the results of processing of radar measurement data, are presented.