Hideki Ninomiya

Raman lidar system for hydrogen gas detection

A Raman lidar system for detection of hydrogen gas has been developed. The lidar system consists of a pulsed Nd:YAG laser of wavelength 355 nm and a Newtonian telescope of aperture 212 mm. The system can detect hydrogen gas by either rotational or vibrational Raman backscatter up to a distance of 30 m in outdoor, daylight conditions. Furthermore, the system can perform two-dimensional mapping of the hydrogen gas distribution by spatial scanning of the laser beam within the telescope field of view.

Compact Raman lidar for hydrogen gas leak detection

A compact Raman lidar system for hydrogen gas leak detection was constructed. Laser-induced fluorescence at a distance of 70 m and Raman scattering light from N2 gas at short range could be detected.

Remote sensing of hydrogen gas concentration distribution by Raman lidar

Hydrogen is expected to become an energy source in the next generation. Although hydrogen gas is a combustible gas with a large explosion concentration range, leakage is presently monitored by contact type gas sensors. The technology for locating a leak and remote sensing of gas concentration distribution is required in case of hydrogen gas leaks. In this study, remote sensing technology of hydrogen gas concentration distribution using a Raman lidar was developed. The lidar system consisted of a pulsed Nd:YAG laser of wavelength 354.7 nm and a Galilean telescope of aperture 170 mm. The system could detect hydrogen gas by vibrational Raman scattering. In this method, hydrogen gas concentration could be measured based on the ratio of the Raman scattering signals from hydrogen gas and from atmospheric nitrogen, which were simultaneously measured. In this manner, the geometrical form factor of the biaxial lidar and the instrumental function were canceled. Hydrogen gas concentration of 0.6-100% could be measured at a distance 13m using this system.

Optical design for in-line typed compact lidar

An in-line typed lidar optics for short range atmosphere sensing and gas detection was designed. Restricting the receivers field of view, the signal-to-noise ratio of the in-line typed lidar echo had little change within the measurement range.

Visualization of hydrogen flame by differential imaging in the ultraviolet region

Hydrogen flame, which emits only in the ultraviolet and infrared regions and is therefore invisible, was visualized by imaging at 309 nm, which corresponds to the peak in the OH emission. The background was imaged simultaneously at 337 nm, where the flame emission is very weak. Both images were obtained using narrowband interference filters of 1.5 nm bandwidth and image intensifiers, and the flame image was extracted from the difference in the intensity of the images at the two wavelengths. A combination of (1) digitization using a threshold intensity level and (2) Gaussian blur were applied to the difference image for rejection of spurious spots which resulted from the grainy appearance of the image obtained by the image intensifier. This method allowed elimination of reflected sunlight. The method was also used to image hydrogen flame using interference filters of 10 nm bandwidth. The flame region was successfully extracted up to a working distance of 30 m under outdoor daylight conditions.