SAR-GPR is a sensor system composed of a GPR and a metal detector for landmine detection. The GPR employs an array antenna for advanced signal processing for better subsurface imaging. This system combined with synthetic aperture radar algorithm, can suppress clutter and can image buried objects in strongly inhomogeneous material. SAR-GPR is a stepped frequency radar system, whose RF component is a newly developed compact vector network analyzers. The size of the system is 30cm x 30cm x 30cm, composed from 6 Vivaldi antennas and 3 vector network analyzers. The weight of the system is less than 30kg, and it can be mounted on a robotic arm on a small unmanned vehicle. In the signal processing of the SAR-GPR has a unique future. It can be used with an algorithm for strong clutter suppression. The sensor has about 10cm offset from the ground surface, and it can even image the ground surface topography. It will be implemented for more advanced imaging algorithm, which can be used for the ground surface with a large roughness. Field tests of SAR-GPR were carried out in March 2005 in Japan. Then after, it was also evaluated in the Netherlands and Croatia. We report the results of these evaluation and demonstration.
SAR processing (or diffraction stacking migration) is an important signal processing method for ground penetrating radar (GPR) in many application case including landmine detection. It can improve signal-clutter ratio and reconstruct subsurface image, summing amplitudes along the hyperbolic trajectory that is Huygens surface (or diffraction travel time surface). For SAR processing, the travel time surface generally is smooth spherical surface in the case of zero-offset data and smooth ellipsoidal surface in the case of nonzero-offset data whose curvature is governed by the velocity function. But when the height of ground surface varies largely in the very rough ground area, for example mound, the travel time surface will be affected by the ground surface for the synthetic aperture - ground penetrating radar (SAR-GPR). In this paper we will consider the effect of the ground surface into the migration processing for the multi-offset CMP SAR-GPR data set. Firstly, using the SAR-GPR CMP data set, we will build the 3D velocity model including the ground surface topography and the subsurface velocity. Then, depending on the 3D model, we can do the ray tracing and compute the travel time between transmitter, receiver and each subsurface scattering point. At last, using the travel time, we can build the Huygens surface (or diffraction travel time surface) for each scattering point. The Huygens surface is the best migration trajectory. Depending on the Huygens surface and the migration trajectory of the SAR processing, we can discuss the migration aperture for SAR processing in rough ground area.
We developed a hand-held landmine detection sensor system, ALIS (Advanced Landmine Imaging System), combined with a metal detector and GPR (Ground penetrating radar). The system has a CCD camera attached on the sensor handle and can record the MD and GPR signal with the sensor position information. Therefore, it can offer the visual MD image and GPR image, which is used to define targets. But because ALIS is a hand-held system, the sensor position is random when it is operated in the field by human being. Also GPR normally suffers from very strong clutter. To deal with these problems, the interpolation is a common choice for both MD and GPR to create grid data set firstly and migration was used to improve the quality of GPR image. But generally the interpolation can not improve the quality of data set, although it can offer grid data set for visualization. Also for 3D GPR data set, it will consume much processing time. In fact, the migration can not only improve the quality of GPR data but also interpolate data to offer grid data set. It is a kind of 2.5D interpolation and just uses related data in the diffraction trajectory surface. So it can offer directly the visual GPR image and save the processing time. We will discuss two procedures for GPR, interpolation + migration or only migration, in this paper. Lastly, we also will report some results of evaluation test in 2006 February in Croatia.
We are developing a new landmine detection sensor (ALIS) which is equipped with a metal detector and a GPR. Although this is a hand-held system, we can record the metal detector and GPR signal with the sensor position information. Therefore, signal processing for 2-D signal image is possible. For the metal detector, we apply cross-correlation algorism for sharpening the image and estimation of the depth of the target. For GPR signal, we can apply migration algorithm, which drastically reduce the clutter and we can obtain 3-D image of the buried targets. At first, linear interpolation and cubic interpolation are used respectively to deal with the problem of random data position. Comparing results, we find the image quality of two kinds of interpolations is almost same. Then the migration is used to refocus the scattered signals and improve the image quality for reconstructed landmine image. ALIS demonstration were held in Afghanistan in December 2004 and other countries including Egypt and Croatia in 2005. After some demonstrations and evaluation, we received many useful suggestions. Using these advises, we have modified the ALIS and it is now more easy to use. In this paper, we describe the latest characteristics of the ALIS and summarize its operation.
Currently there are a few projects for landmine detection in Afghanistan, which is supported by the Japanese government. Some field test for landmine detection sensors have been carried out in Afghanistan and Japan. We introduce in this paper about the plan of these projects, and its evaluation tests. JST (Japan Science and Technology Agency) which is under the Ministry of Education, Culture, Sports, Science and Technology (MEXT)) is developing unmanned vehicles which are mounted sensors for AP landmine detection. The prototype of the sensors and equipments will be ready by February 2005 and will be tested in a test site in Japan by March 2005. Then, it is planned to be evaluated in Afghanistan in summer 2005. JICS (Japan International Cooperation System) which is under the Ministry of Foreign affairs (MOFA) has a project on "Developing Mine Clearance related equipment in Afghanistan". In this project, we plan to evaluate mine detectors in Afghanistan until March 2005. The evaluation test of JICS project has already started in August-Deecember 2004, in Afghanistan,. In the evaluation the both projects, we are preparing test lanes. Most of the sensors to be evaluated is a combination of a metal detector and GPR, and as for GPR, there has been not many examples of such evaluation tests. In this paper, we introduce the outline of the evaluation test, and also discuss some technical aspects of the evaluation test for the combination sensors of a metal detector and a GPR.
The height variation of ground surface and incorrect velocity will affect imaging processing of landmine. To eliminate these effects, ground surface topography and velocity model are needed. For effective detection of landmines, a stepped-frequency continuous-wave array antenna ground penetrating radar system, called SAR-GPR, was developed. Based on multi-offset common middle point (CMP) data acquired by SAR-GPR, we describe a velocity model estimation method using velocity spectrum technique. Also after pre-stack migration, the ground surface can be identified clearly. To compensate landmine imaging for the effect created by height variation, the ground surface displacement, a kind of static correction technique, is used based on the information of ground surface topography and velocity model. To solve the problem of incorrect velocity, we present a continuous variable root-mean-square velocity based on the velocity model. The velocity is used in normal moveout correction (NMO) to adjust the time delay of multi-offset data, and also applied to migration for reconstruction of landmine image. After the application of ground surface topography and velocity model to data processing, we could obtain good landmine images in experiment.
SAR-GPR is a sensor system composed of a GPR and a metal detector for landmine detection. The GPR employs an array antenna for advanced signal processing for better subsurface imaging. This system combined with synthetic aperture radar algorithm, can suppress clutter and can image buried objects in strongly inhomogeneous material. SAR-GPR is a stepped frequency radar system, whose RF component is a newly developed compact vector network analyzers. The size of the system is 30cm x 30cm x 30cm, composed from 6 Vivaldi antennas and 3 vector network analyzers. The weight of the system is less than 30kg, and it can be mounted on a robotic arm on a small unmanned vehicle. The field test of this system was carried out in March 2005 in Japan, and some results on this test are reported.
We are developing a new landmine detection system, called advanced landmine imaging system (ALIS), which is equipped with metal detector (MD) and ground penetrating radar (GPR). Although this is a hand-held system, we can record the MD and GPR signal with the sensor position information acquired by CCD camera. Therefore, 2D MD image and 3D GPR image are possible after signal processing. But because ALIS is a hand-held system, the sensor position is random when it is operated in the field. So interpolation processing is used to deal with the problem and offer grid data set for both MD and GPR. Good MD image can be achieved after interpolation. Also, interpolation can prepare good data set for migration to get good horizontal slice image. After interpolation, 3D diffraction stacking migration with migration aperture is used to refocus the scattered signals and enhance the signal-clutter ratio for reconstructed good GPR image. The ALIS was tested in Afghanistan in December 2004 and could achieve good landmine image. Especially, GPR could obtain good image of anti-person (AP) mine buried at more than 20cm depth. Also MD image and GPR image could combine to distinguish mine from metal fragment.
ALIS (Advanced Landmine Imaging System), which is a novel landmine detection sensor system combined with a metal detector and GPR, was developed. This is a hand-held equipment, which has a sensor position tracking system, and can visualize the sensor output in real time on a head-mounted PC display. In order to achieve the sensor tracking system, ALIS needs only one CCD camera attached on the sensor handle. The new hand-held system ALIS is a very compact and do not require any additional sensor for sensor position tracking. The acquired signal from the metal detector and GPR is displayed on the PC display on real time, and the sensor trace can be checked by the operator. At the same time, the operator can visually recognize the signal on the same display. The CCD captured image is superimposed with the GPR and metal detector signal, therefore the detection and identification of buried targets is quite easy and reliable. Field evaluation test of ALIS was conducted in Afghanistan, and we demonstrated that it can detect buried antipersonnel landmines, and can also discriminate metal fragments from landmines.
Ground-penetrating radar (GPR) is an effective subsurface imaging tool for solution to landmine detection, since it can detect both metal and nonmetal objects. But some times in complicated situation, for example, obliquely buried landmine will reduce its efficiency. To solve the problem, a stepped-frequency continuous-wave array antenna ground penetrating radar (SAR-GPR) system was developed. By the antenna array configuration, Common Middle Point (CMP) data can be acquired directly. Based on the CMP data, several seismic signal processing, including velocity spectrum and pre-stack migration, can be used. The velocity analysis technique based on the velocity spectrum was used here, because the velocity is required for migration. Pre-stack migration technique was used to image obliquely buried landmine in their true spatial location and physical shape in the object space. As a migration technique, pre-stack migration can also increase the signal-to-noise ratio of the survey and refocus the scattered signals. Pre-stack migration can be used by diffraction stacking based on the nonzero-offset travel time equation for a point scatterer. Amplitudes are summed along the nonzero-offset diffraction travel time trajectories. Flat ground surface and obliquely buried landmine were simulated in laboratory experiment. After the application of pre-stack migration to the CMP data acquired by SAR-GPR system, the reconstructed target image could be showed clearly.
Proc. SPIE. 5089, Detection and Remediation Technologies for Mines and Minelike Targets VIII
KEYWORDS: Antennas, General packet radio service, Land mines, Radar, Signal processing, Chemical mechanical planarization, Imaging systems, Finite-difference time-domain method, Transmitters, Receivers
A project for developing a compact size GPR system for landmine detection was started. It will be based on stepped-frequency radar system for wider application in various kinds of soil conditions. We have developed a prototype stepped-frequency GPR system for fundamental evaluation of the system. This system uses an array of broadband Vivalidi antennas and operates at 2-6GHz. The system was tested in laboratory and could be used for imaging buried mine-line targets by high resolution. Series of test was carried out by using sand with rough surface and inhomogeneous soil. Array signal processing is useful for reduction of clutter from the rough grounds surface.