Jun Fujiwara

Development of a hand-held GPR MD sensor system (ALIS)

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.

Development of the Hand held dual sensor ALIS and its evaluation

GPR has been thought a useful sensor for detection of buried land mines, but no GPR has been practically deployed in humanitarian demining. Since 2002, we have developed a new hand-held land mine detection dual-sensor ALIS. ALIS is equipped with a metal detector and a GPR, and it has a sensor tracking system, which can record the GPR and Metal detector signal with its location. It makes possible to process the data afterwards, including migration. The migration processing drastically increases the quality of the image of the buried objects. ALIS uses two different GPR systems, namely VNA (Vector Network Analyzer) based GPR and an Impulse GPR. VNA based GPR can provide better quality GPR images, although the impulse GPR is faster and light weight. ALIS evaluation tests have been held in mine affected courtiers including Afghanistan, Croatia, Egypt and Cambodia. In the two-month evaluation test in Cambodia, ALIS worked without any problem. After some demonstrations and evaluation, we got many useful suggestions. Using these advises, we have modified the ALIS and it is now more easy to use. ALIS will be commercialized in 2007.

ALIS evaluation tests in Croatia

Tohoku University, Japan is developing a new hand-held land mine detection dual-sensor (ALIS) which is equipped with a metal detector and a GPR. ALIS is equipped with a sensor tracking system, which can record the GPR and Metal detector signal with its location. The Migration processing drastically increases the quality of the imaging of the buried objects.Evaluation test of ALIS has been conducted several test sites. Tests in real mine fields in Croatia has been conducted between December 2007 and April 2008. Under different soil and environment conditions, ALIS worked well. Then ALIS evaluation test started in Cambodia in February 2009 and we could find discrimination capability of ALIS in test lanes, and we are planning to start evaluation test in real mine fields in Cambodia.

The development of the hand-held dual-sensor ALIS

Since 2002, we have developed a new hand-held land mine detection dual-sensor ALIS. ALIS is equipped with a metal detector and a GPR, and it has a sensor tracking system, which can record the GPR and Metal detector signal with its location. It makes possible to process the data afterwards, including migration. The migration processing drastically increases the quality of the image of the buried objects. The new system, we do not need any standard mark on the ground. Also, ALIS uses two different GPOR systems, including VNA (Vector Network Analyzer) based GPR and an Impulse GPR. VNA based GPR can provide better quality GPR images, although the impulse GPR is faster and light weight. ALIS evaluation tests were held in mine affected courtiers including Afghanistan, Croatia, Egypt and Cambodia. In the two-month evaluation test in Cambodia, ALIS worked without any problem. After some demonstrations and evaluation, we got many useful suggestions. Using these advises, we have modified the ALIS and it is now more easy to use. ALIS will be commercialized in 2007.

Vehicle-mounted SAR-GPR and its evaluation

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.

Imaging algorithm of a hand-held GPR MD sensor system (ALIS)

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.

Estimation of ground surface topography and velocity model by SAR-GPR and its application to landmine detection

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.

Development of an array-antenna GPR system (SAR-GPR)

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.

Proposal of design method for fixed wireless telecommunication in 400-MHz band and measurements of propagation inside office buildings

There is no clear design guide for fixed wireless links for instrumentation in office buildings. In fact, there are no quantitative data for the propagation and fading characteristics to be utilized in link design. This article intends to provide a design guide for intermittent communication links for instrumentation in office buildings. The approach is as follows. The case where only instantaneous variation with time exists is considered. The receiver power level required to satisfy the specified transmission quality is determined. The variation of the central value depending on the site is represented as a function of the distance between the transmitter and the receiver. By superposing the variation of the central value of the site on the specified distance and variation of the instantaneous value, the zone periphery outage probability is derived, based on the case where the required transmission quality is not maintained. Then, a design guide based on the communication distance is proposed so that the outage probability is kept below the specified value. The communication completion rate is measured quantitatively by a long-term check of communication incompletion cases. The propagation characteristics of electromagnetic waves are measured for the 400-MHz band in an actual office environment. It is shown by experiments that the variation of the received power level follows the Rayleigh distribution and the distance attenuation follows an exponential function, as in a waveguide. Design of a link is attempted for an air-conditioner wireless telecontrol system, using the proposed communication distance estimation based on coefficients determined by experiment. The communicable distance is estimated as 21 m on the same floor with a seven-fold code redundant selective SD antenna. It is estimated that the required transmission quality cannot be realized in communication to adjacent floors. The communicable distance is estimated as up to 14 on in the same floor by the selective SD antenna, when the seven-fold extended code is not used.

Development of handheld dual-sensor ALIS and its evaluation

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.