Hiroyuki Ishizaki

A model of the Kakkonda geothermal reservoir

Abstract Reservoir pressures, temperatures and chloride concentrations are interpreted from well measurements in the Kakkonda geothermal field (Japan), to obtain a natural state conceptual model and to determine changes in the reservoir subsequent to production and reinjection. In this model the system is viewed as two reservoirs, a shallow reservoir extending from the surface to about 800 m below sea level and, partially isolated from this, a deep reservoir extending down to 3000 m below sea level. The modelling of the changes has taken two forms, one a lumped-parameter mathematical model leading to an expression for the average reservoir chloride concentration as a function of time, and the other a three-dimensional numerical simulation model. The mathematical model is fitted to pressure and chloride concentration changes. The numerical model is fitted to the natural state pressures, temperatures and chloride concentrations, and is verified by comparing the predicted variation of production enthalpy with the measured changes. The numerical model is also used to explore a simplified development scenario, involving a production/injection flow doublet, thus allowing a clearer interpretation of thermal and chemical travel times across the reservoir.

Development of LPE-grown HgCdTe 64 x 64 FPA with a cutoff wavelength of 10.6 μm

We have developed a hybrid HgCdTe focal plane array (FPA) for wavelengths from 8 to 11 micrometers . We describe how we fabricated our back illuminated 64 X 64-element photodiode array on a liquid phase epitaxial (LPE) HgCdTe wafer, and a Si CCD multiplexer with line address readout. We optimized carrier concentration in the p-type HgCdTe layer to maximize charge injection efficiency to the Si CCD readout circuit to more than 99.3%. We achieved excellent uniformity of characteristics of the photodiode array, which is very important for an IRFPA, by using LPE HgCdTe grown with a tipping method, and passivating the photodiode array with an anodic sulfide of HgCdTe. We obtained an average product of zero-bias resistance and area (RoA) of 9.1 (Omega) cm2 with a cutoff wavelength of 10.6 micrometers at 77 K. We used line address readout to give a large charge storage capacity of 4 X 107 electrons. We estimated a noise equivalent temperature difference (NETD) of 0.08 K with F/2.5 optics, including fixed pattern noise. We tried some preliminary experiments to reduce the crosstalk from photogenerated carriers which spread laterally into the epitaxial layer. We improved the modulation transfer function (MTF) at Nyquist spatial frequency from the conventional 35% to 60% by using a crosswise drain structure around each photosensitive n+ on p diode.

Resolution improvement for HgCdTe IRCCD

This paper describes a resolution improvement for a mercury cadmium telluride (MCT) infrared charge-coupled device (IRCCD) using a new microscanner. To keep the microscanner compact, the scanner prism is placed between the lens and the IRCCD, and driven by a bimorph piezoelectric actuator. By compensating the drive pulse and optimizing the prism thickness, the microscanner gives a fast and stable response with low distortion. The medium wavelength imager developed for the microscanner gives a 128 X 128 pixel thermal image in the 3 to 5 micrometers band using a 64 X 64 element IRCCD. The Nyquist frequency was increased from 10 to 20 cycles/mm to reduce aliasing without decreasing the S/N ratio. The noise equivalent temperature difference (NETD) was measured at 0.06 K with an f-1.7 lens. The modulation transfer function (MTF) was estimated by considering the scan distortion and the pixel aperture profile. By optimizing the aperture profile of the photodiode, the MTF at the Nyquist frequency was increased from 0 to 20%.

A Highly Sensitive And Compact SO2 Gas Sensor Using A Pbsnte Laser

We have developed a highly sensitive, compact SO2 gas sensor that uses a PbSnTe laser. To increase its sensitivity, we used wedge-shaped windows that decrease etalon fringes and a SO2 absorption line that is little influenced by water vapor and that has a strong coefficient. The etalon-fringe intensity of the optical system was reduced to 1 x 10-4 and the SO2 absorption line selected is 1380.9 cm-1. To make the sensor compact, we developed single-mode lasers to eliminate the need for a monochromator, used a 30-cm multipath cell with an optical path of 10 m and a liquid-nitrogen-cooled, small metal dewar to cool the laser. The sensor performs stably at 30 ppb over a range of 10°C to 35°C, has a sensitivity of 7 ppb RMS at a fixed temperature, and is 32 cm x 50 cm x 20 cm.

Parallel-Scan Thermal Imager With A Thermoelectrically Cooled Multielement Detector

This paper describes the design and performance of a low-cost parallel-scan thermal imager. The sensor, with a 16-element photoconductive HgCdTe detector, employs a thermoelectric cooler that has the advantages of low life cycle costs, relatively light weight, and high reliability. The scanner is a rotating polygonal mirror with different degrees of tilt on the facet faces, which allows buildup of the square format in object space. This type of scanner has a simple structure and is suited for high-speed operation. In order to lower production costs, an aluminum polygonal mirror, manufactured by precision single-point diamond turning, has been developed. The system has the following parameters, determined by making a trade-off study among performance, size, and cost: field of view, 14.7° x 14.7°; angular resolution, 2 mrad; aperture of focal optics, 23 mm; frame rate, 20 Hz; resolution, 128 x 128 lines; and NETD, 0.6°C.