Yuya Yokota

ALIS : GPR System for Humanitarian Demining and Its Deployment in Cambodia

Humanitarian demining is very important issue not only in mine affected courtiers but also for the courtiers which are technically, politically and financially supporting the mine affected courtiers. In order to achieve higher efficiency of the mine clearance operation, new technologies can significantly contribute to the societies. Since 2002, Tohoku University, Japan has developed a sensor system “ALIS” for humanitarian demining. ALIS is a hand-held dual sensor, which combines an electromagnetic induction sensor (EMI) and a Ground Penetrating Radar (GPR). ALIS has a real-time sensor tracking system based on a CCD camera and which enables the image reconstruction. We have tested ALIS in Cambodia and found that it can eliminate more than 70 % metal fragments. Since 2009, 2 sets of ALIS have detected more than 80 anti-personnel mines, and cleared more than 137,000 ㎡ in Cambodia.

Development of multichannel intermediate frequency system for electron cyclotron emission radiometer on KSTAR Tokamak

Plasma experiments on KSTAR are scheduled to start up this year (2008). We have developed an electron cyclotron emission (ECE) radiometer to measure the radial electron temperature profiles in KSTAR experiments. The radiometer system consists, briefly, of two downconversion stages, amplifiers, bandpass filter banks, and video detectors. These components are made commercially or developed in house. The system detects ECE power in the frequency range from 110 to 196 GHz, the detected signal being resolved by means of 48 frequency windows. Before installation of this system on KSTAR, we installed a part of this system on large helical device (LHD) to study the system under similar plasma conditions. In this experiment, the signal amplitude, considered to be proportional to the electron temperature, is measured. The time-dependent traces of the electron temperature measured by this radiometer are in good agreement with those provided by the LHD Michelson spectrometer. The system noise level which limits the minimum measurable temperature (converted to the electron temperature) is about 30 eV.

Coherent scatterer in forest environment: Detection, properties and its applications

In this paper, the first detection result of coherent scatterers (CSs) in forest environment is addressed. As a scatterer associated with CS, the dihedral structure consists of the tree-trunk like a vertical cylinder and the ground surface is assumed. The potential of CSs as being the phase stable scatterers as permanent scatterers will be also demonstrated with P-&L-band Pol-InSAR datasets acquired in repeat-pass InSAR mode over boreal forest test site by German Aerospace Centers E-SAR airborne system.

Remote experiment of ultrashort-pulse reflectometry for large helical device plasmas

An ultrashort-pulse reflectometer (USPR) has been applied to the large helical device plasmas in National Institute for Fusion Science for edge density profile measurement. Remote control system using super science information network has been introduced to the USPR system. The remote console at Kyushu University having graphical user interface is prepared to control the instruments of the USPR via the general-purpose interface bus. The operations such as the adjustment of supply voltage fed to amplifiers and the frequency doubler, timing control of the impulse, data acquisition, and monitoring can be performed from the remote site. The position of transmitter and receiver antennas can also be controlled remotely in order to observe the cutoff layer depending on various plasma conditions. The directly recorded signal by a sampling scope is analyzed and reconstructed by means of the signal record analysis method.

Estimation of biomass of tree roots by GPR with high accuracy positioning system

A new approach for estimation of the tree root biomass is proposed by using GPR system with high accuracy positioning system. The 3D images of subsurface can be obtained clearly with this system, which we refer as “3DGPR”. We try to estimate the biomass of tree roots quantitatively by measuring the volume of the tree roots. We tested this system for tree roots measurement, and the broadening of the tree root with horizontal direction could be detected with 500 MHz and 800 MHz antenna. We excavated this tree every 10 cm from 0 cm to 50 cm to validate the accuracy of the result. Compared with the measurement result and the excavated one, the tree root whose diameter is more than 5 cm could be detected correctly. Some tree roots whose diameter is 3 cm also could be detected. The diameter in most of the tree roots is more than 2cm. In this result, we expect that the volume is supposed to be estimated within 30 percent error by using the excavated result for calibration data.

CCD camera and IGPS tracking of geophysical sensors for visualization of buried explosive devices

High-resolution Ground Penetrating Radar (GPR) images of the ground surface and shallow subsurface are needed in order to detect and identify small buried explosive materials such as Anti-Personnel (AP) landmines. A key requirement to produce sharp visualizations is centimetre-precise sensor positioning with real-time imaging results. We are pursuing two complementary approaches to accomplish this task: 1) Sensor tracking with a CCD camera, 2) and large work volume Indoor GPS. In outdoor field tests both methods have successfully imaged small landmine targets, which has a plastic body of less than 10cm diameter.

Measurement of edge density profiles of Large Helical Device plasmas using an ultrashort-pulse reflectometer

We report here on the application of an ultrashort-pulse reflectometer (USPR) to Large Helical Device in National Institute for Fusion Science. An impulse with picosecond pulse width is used as a source in an USPR. Since the bandwidth of a source is inversely related to the pulse width, we can utilize the frequency range of microwave to millimeter-wave by using wide band transmission lines. The density profiles can be reconstructed by collecting time-of-flight signal of each frequency component of an impulse reflected from each cutoff layer. Remote control system using super science information network has been introduced to the present USPR system.

Wide band stepped-frequency ground penetrating radar

The stepped-frequency continuous wave (SFCW) ground penetrating radar (GPR) combined with wideband bow tie antennas and a handheld VNA is successfully demonstrated and compared with three types of commercial pulse GPRs for the detection and identification of the buried targets at depths of 20 cm and 80 cm. It has the performance of the better signal to clutter ratio than all of the tested commercial pulse GPRs for the metal pipe at a depth of 20 cm and also the better range and azimuth resolutions than the pulse GPR having a center frequency of 250 MHz. It is strongly expected to be simultaneously satisfied with the conflicting needs of both deeper penetration and higher resolutions and to be finally replaced all of the tested pulse GPRs.

Monitoring of dynamic groundwater level change by ground penetrating radar for quantitattive estinmation of hydraulic parameters

In order to accurately monitor the dynamic groundwater level change caused by the well pumping in a non-destructive way, we developed Common Mid-Point (CMP) method using Ground Penetrating Radar (GPR). The envelope velocity spectrum and an automatic velocity picking scheme were proposed for the accurate velocity analysis of CMP dataset. We applied the algorithm to the GPR data acquired near Tuul river in Mongolia. The obtained vertical velocity profile was converted to the vertical water content profile, in which the groundwater level could be easily identified. In this measurement, a groundwater level rise of 0.21 m was observed after the pumping was stopped. The dynamic groundwater level change estimated by GPR was used to estimate the hydraulic conductivity of the unconfined groundwater aquifer. The result agreed well with a previous study.

Data interpolation and resampling for a synthetic aperture radar data

In this paper, we introduce interpolation for a detailed observation of synthetic aperture radar (SAR) data. The interpolation is done by zero-padding in the frequency domain. By comparing the raw SAR data and the interpolated data, for example, it is observed that the raw span at a corner reflector we deployed is 0.75 times smaller than its real values. Also, we propose a resampling method applied to the interpolated data to keep data amount same as raw data. The proposed method resamples points where peaks of the span due to coherent targets exist. As for pixels where the peak does not exist, points with the smallest polarimetric entropy are selected. The proposed method is compared to raw data and the resampled data by the maximum filter. It is confirmed that the proposed data emphasizes the characteristics of the raw data. Also, its blurring effect is not as much as that in the resampled data by the maximum filter. This technique is quite basic, however, the effect is not negligible.