椎名 達雄

The LED mini lidar was improved to monitor Raman scattering echoes. The Raman scattering signal indicates a certain gas concentration and it can distinguish the target from the other materials. It is so weak, 1/1000 of Mie scattering echoes, but even enough to be stimulated from the target gas with LED pulsed beam. At first, we developed a compact Raman lidar with micro pulse DPSS laser to detect hydrogen gas quantitatively. We replaced it with the LED pulse module, which was calculated enough potential to stimulate Raman scattering and detect the target gas. The next task is the activity measurement of such a target gas. To validate the potential of the LED Raman lidar, we conducted the sea surface atmosphere measurement. As a result, the unique relationship between the surface atmosphere and sea water echoes was observed. In this report, we state the concrete specification of the LED mini Raman lidar and some results of the activity observations.

The combined use of remote sensing and in-situ monitoring instruments could help improve the assessment of near-surface aerosol properties. In this paper, we analyze the diurnal behavior of aerosol extinction coefficients, alpha(Ext)(lambda), at lambda=349 and 550 nm using a lidar and a present weather detector, respectively. We utilize the aerosol optical thickness (AOT), single scattering albedo (SSA), and Angstrom exponent (AE) from SKYNET sky radiometer, and AE from aethalometer, and the number distribution from optical particle counter to evaluate the effect of relative humidity (RH) on aerosol extinction coefficients. It is found that although alpha(Ex)(lambda) often exhibits a positive correlation with the ambient RH, this relation is obscured when both the number distribution and particle size change simultaneously. Moreover, alpha(Ext) at 349 nm is more sensitive to this change than at 550 nm.

A compact LED lidar was constructed and fieldtested with the aim to observe the Mars' dust devils. To be able to fit it on the Mars rover, a specialized Cassegrain telescope was designed to be within a 10 cm-cube, with a field of view of 3mrad. The transmitter has 385 nm LED light source with 3 cm opening, 70mrad divergence, 0.75W (7.5nJ/10ns) pulse power, and 500 kHz repetition frequency. The configuration of the optical system is biaxial to easily configure the overlap between their optical axes.

© 2018 SPIE. We focused on the propagation property of an annular beam in strong scattering random media such as nimbostratus or dense fog. An annular beam as a lidar transmitted beam can propagate a longer distance even through atmospheric fluctuation. The reason is that an annular beam can self-transform to a non-diffracting beam, which is called non-diffractive effect. In this work, the center peak intensity as result of non-diffractive effect was generated after the propagation of an annular beam in random media with different concentrations and propagation distances. The linear relationship between the propagation distance and the transport mean free path calculated from the media concentration that caused the maximum center peak intensity was obtained. The generation condition of the non-diffractive beam was discussed under arbitrary parameters of beam diameter, propagation distance and media concentration.

A compact Raman lidar has been developed for studying phase changes of water in the atmosphere under the influence of ionization radiation. The Raman lidar is operated at the wavelength of 349 nm and backscattered Raman signals of liquid and vapor phase water are detected at 396 and 400 nm, respectively. Alpha particles emitted from Am-241 of 9 MBq ionize air molecules in a scattering chamber, and the resulting ions lead to the formation of liquid water droplets. From the analysis of Raman signal intensities, it has been found that the increase in the liquid water Raman channel is approximately 3 times as much as the decrease in the vapor phase water Raman channel, which is consistent with the theoretical prediction based on the Raman cross-sections. In addition, the radius of the water droplet is estimated to be 0.2 mu m.

Atmospheric Data Collection Lidar (ADCL) of the Center for Environmental Remote Sensing (CEReS), Chiba University, is a multi-wavelength lidar system designed for measuring tropospheric aerosols and clouds with ancillary data from ground-based aerosol measurement instruments. In this paper, we report on the concept of aerosol and cloud retrieval based on vertical, slant-path, and plan-position indicator (PPI) lidar measurements in combination with aerosol measurements conducted with a three-wavelength integrating nephelometer, an aethalometer, and a particle counter. It is expected that such a combined approach makes it possible to study the detailed features of aerosols in the troposphere, including the aerosol-cloud interaction.

Nowadays air-flow and certain gas measurements in near range are needed as a lidar application. Lidar optics, however, has blind area because it takes a certain distance to overlap the transmitting beam and the receiver's field of view. To detect the near range lidar echo with the narrow field of view, the optical design should be adequate. In this study, several cases of concrete lidar systems for near range measurement will be introduced. The near range compact Raman lidar applications, here the author mainly explain, are hydrogen leakage gas detection up to 50m ahead, monitoring exhaust fume at an intersection, air-flow measurement for a closed space such as a exhibition hall, and so on. The system should be compact as the near range lidar. The optical design should be simple to accomplish the near range measurement. The author has started the theoretical calculation of the lidar echo simulation with the various types of optical designs such as biaxial, coaxial and inline optics, which has common optics for the transmitting and receiving optics. The signal-to-noise ratio will be also estimated in the viewpoint of lowering transmitting beam power for eye-safe. The near range from zero to a few hundred meters is a target distance. The calculated results were compared and evaluated with the optical specification of the actual lidar. Now, the studies are extended, and the several types of near range lidars were developed mainly for the disaster prediction. They are certain gas detection, heavy rain prediction and lightning stroke detection. The "inline" optics adapt to the various kinds of lidar techniques, such as usual Mie lidar, Raman lidar, and polarization lidar. In this report, such a variety of the inline lidars are also introduced.

An Optical coherence tomography system (OCT system) was developed to measure physiological response inside plant. This system has a unique optical scanner of wide scanning range of 40mm to adapt the OCT measurement to irregular features and many breeds of plant samples. To use in the outdoor field, which plants volunteers, the system should be compact, stable, and have high repetition frequency of measurement. We designed the OCT system with the original optical scanner and optical fiber optics for the purpose. The transmittance and reflectance characteristics of the plant leaves were examined to check the water absorption. The SLD-light of the wavelength of 830nm was selected for the measurement light source. Various kinds of plant samples were measured to evaluate the system performance and its adaptive flexibility. Cell structure of plant surface, its change due to the water content, and growth monitoring of plant tissue were measured. The concrete application was also demonstrated.

The in-line type Micro Pulse Lidar (MPL) has been developed. This in-line MPL has the advantages of near distance measurement with the narrow field of view, utilization of an annular beam and simultaneous measurement of the orthogonally polarized echoes. This report states the improvement of the system performance and evaluation of hard target and cloud measurements with the in-line MPL. The usual in-line MPL had had a serious problem that the detectors could not obtain the enough responsivity especially in near distance measurement because the directly reflected light from the optics made at it. In this study, an optical circulator and a couple of Axicon prisms, which generate an annular beam, have been installed into the lidar optics. Here, all of the optical components had small tilts against the optical axis. We dispensed rigorous alignment for the lidar optics. As a result, the detectors (APD) could be supplied the inverse voltage up to the breakdown with the analog mode. It leads not only the simultaneous measurement of the orthogonally polarized echoes of hard targets from the nearest distance without dead time, but also the depolarization measurement of cloud ice crystals. Furthermore, we state the annular beam propagation in the atmospheric turbulence.

多モード干渉光導波路を用いた4端子対型の導波型マジックTを提案し、FDTD法による動作確認を行った結果について述べる。この素子の構造は、対称多モード干渉光導波路と薄膜を装荷した非対称多モード干渉光導波路を組み合わせることで構成される。薄膜装荷による非対称多モード干渉光導波路部分においてモード移行を起こすことでマジックTとして動作する。単純に組み合わせるだけでは分配比が悪く、薄膜装荷を多段式に変更することで分配比の向上を果たした。この素子の利点は直線のみの構造となることから制作上簡素化がはかれる。

近赤外光をプローブに用いることで生体に対し無侵襲・非接触に断層画像を取得できる光トモグラフィー(Optical Tomography)の開発が急がれている。しかし、計測対象となる生体は高散乱体であり、それによる多重散乱の影響が開発の障害となっている。本研究では、その多重散乱光を利用した光トモグラフィーを目指し、拡散光子密度波(DPDW : Diffuse Photon Density Wave)と呼ばれる散乱媒質中の光波に着目した。DPDWは媒質中を球面波状に伝搬するため、その振幅情報と位相情報を検出することにより高散乱体内部の断層画像を再構成できる。本稿では2次元モデルを構築し、特異値分解や正則化などの数学的手法を導入した再構成アルゴリズムを用いて吸収係数、散乱係数の同時再構成を行った。

This study reports the analysis of the long distance propagation characteristics of the annular beam and its application to lidar. In our analysis, the annular beam is formed by a couple of axicon prisms. The waveform of the annular beam is transformed into the nearly nondiffractive beam through the propagation. The propagation characteristics can be easily controlled by the waveform of the outgoing annular beam. The center peak intensity, FWHM, and the intensity ratio of the center peak intensity of the transformed nondiffractive beam to the whole beam intensity were examined in the various viewpoints. We also considered the spread and focusing angle of the annular beam, and obtained the critical angle to transform the nondiffractive beam. We confirmed that the permissible error of the optical alignment has an enough margin with the desired beam divergence. The annular beam proves its merit on a co-linear type lidar because of utilization of a large reflecting telescope with high transmitting efficiency and near distance measurement with a narrow FOV.

InGaN系白色発光ダイオード(LED)の発光原理から、白色LEDを変調すると、青色光と黄緑色光との間に時間差が生じる。本研究ではパルス、トリガ、ランプそして正弦波によって変調した白色LEDの発振波長特性を明らかにした。パルス変調時、パルス幅によって発光状態は異なり、パルス幅が500nsのとき、青色、白色、黄緑色の順に、パルス幅が60nsのとき、白色、黄緑色の順で発光した。また、トリガ変調では青色、ランプ変調では黄緑色、正弦波変調では白色の発振特性を良く表すことがわかった。白色LEDは変調波形と繰り返し周波数によって青色光と黄緑色光の比率を変化できることがわかった。

ライダーを用いた観測において送受信光学系を同軸上にとるタイプがあるが、その場合送信光と受信光を分離するための工夫が必要となる。これを解決するために光サーキュレータを応用した光学系を製作した。この光サーキュレータは送受信光を分離し、尚且つ偏光成分によりエコー光を分離する性能を満たす。また、軽量・コンパクト(重量1.3kg・30cm四方)であり、望遠鏡鏡筒に固定することができた。光サーキュレータの挿入損失は3dB(波長1.047μm)である。また、望遠鏡鏡筒を動かしてもサーキュレータの光軸には支障がないことを確認している。この光サーキュレータを用いることにより送受信光を分離し、同時にエコー光の偏光成分を分離することができる。これにより小型・可搬なライダーを実現させることが可能となる。

近年、光計測法による微小構造物の内部計測法の研究が盛んに進められている。その1つとして後方散乱光を利用した低コヒーレンス干渉計があるが、機械的な走査機構を必要とするため長深度・高速化は困難であった。本研究では、その問題点の解決としてコーナー反射鏡を利用した可変光路拡大機構を提案し、その基礎実験を行なった。この手法は従来の機構と比べ、長深度かつ高速な計測を可能とする。また、ロックインアンプを利用した微弱光計測にも対応できる。基礎実験では, 中心波長543.5μmのHe-Neレーザを用いた深度距離40mmでの干渉光計測が可能であることを確認した。

In bad weather conditions, e.g. rainy, foggy, and snowy conditions, exact slant visual ranges should be obtained for safe landings at airports. However, no equipment for achieving this has been installed in airports yet. In this study, the laser radar system is refined for estimating the slant visual range. It is found that the empirical data in bad weather conditions do not correspond to predictions with the current laser radar equation. Therefore, a new laser radar equation, which considers the divergence of the transmitting laser beam, is proposed. The slopes of this equation correspond well to the empirical data in various weather conditions. The visibilities estimated by this equation also correspond with those obtained by the slant transmittance system. Also, the extent of the divergence is examined by means of classifying the empirical data by weather conditions. As a result, it is found that the divergence of the transmitted laser beam increases in the order of rain, fog, misty rain, and snow. © 1999, The Illuminating Engineering Institute of Japan. All rights reserved.

In bad weather conditions, e.g. rainy, foggy, and snowy conditions, exact slant visual ranges should be obtained for safe landings at airports. However, no equipment for achieving this has been installed in airports yet. In this study, the laser radar system is refined for estimating the slant visual range. It is found that the empirical data in bad weather conditions do not correspond to predictions with the current laser radar equation. Therefore, a new laser radar equation, which considers the divergence of the transmitting laser beam, is proposed. The slopes of this equation correspond well to the empirical data in various weather conditions. The visibilities estimated by this equation also correspond with those obtained by the slant transmittance system. Also, the extent of the divergence is examined by means of classifying the empirical data by weather conditions. As a result, it is found that the divergence of the transmitted laser beam increases in the order of rain, fog, misty rain, and snow. © 1999, The Illuminating Engineering Institute of Japan. All rights reserved.