355-nm direct-detection Doppler wind lidar for vertical atmospheric motion measurement.

A compact and simple 355-nm direct-detection Doppler wind lidar (DDDWL) was developed to measure the line-of-sight (LOS) wind speed of the background atmosphere from atmospheric molecule return signals with and without aerosols and clouds. A receiver design with a Fabry-Perot etalon interferometer (FPEI) without an inside deposited step coating or fiber coupling is considered for the DDDWL using the double-edge technique. The receiver with the double-edge technique uses a FPEI and wedge prism to form a double-edge filter. The development of the double-edge filter in this combination is, to the best of our knowledge, an improvement at 355-nm wavelength. Considerations for the DDDWL receiver with a FPEI revealed that a full-angle light beam divergence into the FPEI and a working FPEI aperture are significant factors for the receiver design. Preliminary experimental evaluation demonstrated that the DDDWL had the potential of LOS wind speed measurements with a random error of less than 1 m/s when the signal-to-noise ratio was approximately 300. The DDDWL-measured vertical LOS wind speed profile was consistent with that of a 2-µm coherent Doppler wind lidar within the measurement error range. The preliminary experimental LOS wind measurement results demonstrated the capability of the DDDWL to measure low LOS wind speeds.

Demonstration of aerosol profile measurement with a dual-wavelength high-spectral-resolution lidar using a scanning interferometer.

Simple dual-wavelength high-spectral-resolution lidar at 355 and 532 nm with a scanning interferometer was developed for continuous observations of aerosol profiles. Scanning the interferometer periodically over a range of one fringe at 532 nm (1.5 fringes at 355 nm) enabled recording of range-resolved interference signals at these two wavelengths. Reference signals taken from the transmitted laser were used to correct the interference phase shift due to laser frequency variation for every scan. Profiles of aerosol backscatter and extinction coefficients were retrieved from range-resolved interference data. One month of continuous measurements demonstrated the robustness of the system.

Possible use of fluorescence from iodine blocking filter in high-spectral-resolution lidar to detect Mie scattering signals.

The detection of atmospheric backscattering signals using fluorescence from an iodine blocking filter in high-spectral-resolution lidar was studied experimentally. The efficiency of detection is determined by the fluorescence quantum efficiency and the optical efficiency of collecting fluorescence. The quantum efficiency was estimated to be ${\sim}{0.08}$ from the measured fluorescence lifetime of 0.18 µs and the radiative lifetime of 2.3 µs estimated from the literature. The efficiency of collecting fluorescence was low (${\sim}{0.008}$) in the current system. Measurements of atmospheric backscattering were performed, and it was confirmed that the method actually detected the Mie scattering component of the signal.

Development of a 355-nm high-spectral-resolution lidar using a scanning Michelson interferometer for aerosol profile measurement.

A simple 355-nm high-spectral-resolution lidar (HSRL) is developed for continuous observation of aerosol profiles. A scanning Michelson interferometer is used to separate the Rayleigh and Mie scattering components. The interferometer is periodically scanned in the range of one fringe. Interference contrast, which contains aerosol backscatter information, is estimated at each height through fitting analysis of the scan data. The interference contrast and fringe position are calibrated with the reference signals taken from the transmitted laser. Furthermore, the 1-day continuous measurement of aerosol backscatter and extinction coefficients is demonstrated. Comparison with a nighttime Raman lidar indicates a good performance of the scanning method.

Measurement of water mist particle size generated by rocket launch using a two-wavelength multi-static lidar.

Water mist generated during a rocket launch is thought to protect the rocket and payloads from acoustic noise. The size of mist particles is essential to understanding the effect on noise reduction. A two-wavelength multi-static lidar was developed for measuring water mist size at the launch site. The lidar determines particle size from signals at three scattering angles at two wavelengths. The method was tested with artificial mist and applied to the Japan Aerospace Exploration Agency's H-IIA/B large-scale rocket launches. The measured particle size near the outside edge of the mist cloud was 3.5-5 µm in diameter. The extinction coefficient at 532 nm derived using the Klett backward inversion method was 100-200 km-1. The estimated liquid water content (LWC) was ∼0.3 g/m3. The extinction coefficient was high, but the LWC was comparable to that of the water clouds.

Measurement method of high spectral resolution lidar with a multimode laser and a scanning Mach-Zehnder interferometer.

A simple high spectral resolution lidar technique using a multi-longitudinal mode laser is proposed for measuring aerosol extinction and backscattering coefficients. A scanning interferometer having the same free spectral range as the mode spacing of the laser is used to separate Rayleigh from Mie scattering. Scanning the interferometer in the span of one fringe, the lidar signals at the minimum and maximum Mie-scattering transmission are measured. The Rayleigh scattering signal is analyzed from these signals, and the aerosol extinction coefficient is derived. The interferometer transmittance for Mie scattering is calibrated with the reference signals taken with a portion of the transmitted laser beam.

Real-time observational evidence of changing Asian dust morphology with the mixing of heavy anthropogenic pollution.

Natural mineral dust and heavy anthropogenic pollution and its complex interactions cause significant environmental problems in East Asia. Due to restrictions of observing technique, real-time morphological change in Asian dust particles owing to coating process of anthropogenic pollutants is still statistically unclear. Here, we first used a newly developed, single-particle polarization detector and quantitatively investigate the evolution of the polarization property of backscattering light reflected from dust particle as they were mixing with anthropogenic pollutants in North China. The decrease in observed depolarization ratio is mainly attributed to the decrease of aspect ratio of the dust particles as a result of continuous coating processes. Hygroscopic growth of Calcium nitrate (Ca(NO3)2) on the surface of the dust particles played a vital role, particularly when they are stagnant in the polluted region with high RH conditions. Reliable statistics highlight the significant importance of internally mixed, 'quasi-spherical' Asian dust particles, which markedly act as cloud condensation nuclei and exert regional climate change.

Effect of desert dust exposure on allergic symptoms: A natural experiment in Japan.

BACKGROUND: Desert dust originating from arid and semiarid areas is transported to widespread regions, including Japan. Desert dust particles exert adjuvant effects in animals. OBJECTIVE: To examine whether desert dust enhances allergic symptoms in real-life settings and to explore its effect modifiers. METHODS: We conducted an observational study of 3,327 pregnant women during spring and fall in October 2011 to May 2013 in 3 regions in Japan as an adjunct study of the Japan Environment & Children's Study. We acquired participants' daily symptom scores by sending a questionnaire to their mobile phones on high desert-dust days (>0.07/km) and on some randomly selected other days (control days) for each participant. RESULTS: Pregnant women had an increased risk of allergic symptoms on high desert-dust days (adjusted odds ratio [OR], 1.10; 95% CI, 1.04-1.18). The increased OR was mostly driven by those who showed positive IgE to Japanese cedar pollen when pollen simultaneously dispersed (adjusted OR, 1.25; 95% CI, 1.13-1.38), whereas no clear risk increase was observed in the absence of pollen or for participants with negative IgE to Japanese cedar pollen. The risk elevation was observed from low levels of desert dust in a dose-dependent manner even on control days. CONCLUSION: Ambient desert dust level was associated with an increased risk of allergic symptoms in pollen-sensitized pregnant women when pollen was present in the air. The risk increase was dose dependent and was observed from low levels of desert dust. These results support a hypothesis that ambient desert dust particles exert adjuvant effects in human in real-life settings. TRIAL REGISTRATION: clinicaltrials.gov Identifier: UMIN000010826.

Development of a multiple-field-of-view multiple-scattering polarization lidar: comparison with cloud radar.

We developed a multiple-field-of-view multiple-scattering polarization lidar (MFMSPL) to study the microphysics of optically thick clouds. Designed to measure enhanced backscattering and depolarization ratio comparable to space-borne lidar, the system consists of four sets of parallel and perpendicular channels mounted with different zenith angles. Depolarization ratios from water clouds were large as observed by MFMSPL compared to those observed by conventional lidar. Cloud top heights and depolarization ratios tended to be larger for outer MFMSPL channels than for vertically pointing channels. Co-located 95 GHz cloud radar and MFMSPL observations showed reasonable agreement at the observed cloud top height.

Stable dual-wavelength Q-switched Nd:YAG laser using a two-step energy extraction technique.

The generation of stable dual-wavelength pulses from an actively Q-switched Nd:YAG laser operating at 1064 and 1319 nm was demonstrated. Pulse energies of the dual-wavelength laser were extracted by two temporally separated stimulated-emission processes for a single pumping process, thereby avoiding line competition between the two laser transitions. Total energy of the order of 20 mJ was achieved for the two pulses, and the ratio of the pulse energies of the two lasers could be selected by adjusting the output couplings. The pulse-to-pulse fluctuations for the lasers operating at 1319 and 1064 nm were 4.7%-4.8% and 1.5%-2.6%, respectively, which were almost equivalent to those for a single emission line in our system. The experimentally observed laser performance agreed reasonably well with theoretical predictions.

Birth cohort study on the effects of desert dust exposure on children's health: protocol of an adjunct study of the Japan Environment & Children's Study.

INTRODUCTION: Desert dust is estimated to constitute about 35% of aerosol in the troposphere. Desertification, climatic variability and global warming all can contribute to increased dust formation. This study aims to examine possible health effects of desert dust exposure on pregnant women and their children. The purpose of this report was to present the study protocol. METHODS AND ANALYSIS: This 4-year birth cohort study began in 2011 as an adjunct study of the Japan Environment & Children's Study (JECS) involving three regions: Kyoto, Toyama and Tottori. The JECS participants of the three regions above who also agreed to participate in this adjunct study were enrolled prior to delivery. Light Detecting and Ranging (LIDAR) with a polarisation analyser, which can distinguish mineral dust particles from other particles, is used for exposure measurements. Outcomes are allergic symptoms for mothers and development of asthma and other allergic or respiratory diseases for their children. Data are acquired in a timely manner by connecting local LIDAR equipment to an online questionnaire system. Participants answer the online questionnaire using mobile phones or personal computers. ETHICS AND DISSEMINATION: The study protocol was approved by the ethics committees of Kyoto University, University of Toyama and Tottori University. All participants provided written informed consent. The results of this study will be published in peer-reviewed journals and disseminated to the scientific community and general public. TRIAL REGISTRATION NUMBER: UMIN000010826.

Fluorescence from atmospheric aerosols observed with a multi-channel lidar spectrometer.

A lidar for measuring fluorescence from atmospheric aerosols was constructed with a third harmonic Nd:YAG laser, a 1-m diameter telescope, and a 32-channel time-resolved photon-counting spectrometer system. Fluorescence spectrum and vertical distribution of fluorescent aerosols in the lower atmosphere were observed during the nighttime with excitation at 355 nm. Relatively strong broad fluorescence was observed from Asian dust and air-pollution aerosols transported from urban and industrial areas. Rough estimates of the fluorescence efficiency were given for these aerosols. The intensity of the total fluorescence over the spectral range from 420 to 510 nm was comparable to that of nitrogen vibrational Raman scattering. That indicates the possibility of making a compact Raman-Mie-fluorescence lidar for aerosol monitoring.

Lidar measurements of Raman scattering at ultraviolet wavelength from mineral dust over East Asia.

We developed a novel measurement channel that utilizes Raman scattering from silicon dioxide (SiO2) quartz at an ultraviolet wavelength (361 nm). The excitation of the Raman signals is done at the primary wavelength of 355 nm emitted from a lidar instrument. In combination with Raman signals from scattering from nitrogen molecules, we may infer the mineral-quartz-related backscatter coefficient. This technique thus allows us to identify in a comparably direct way the mineral quartz content in mixed pollution plumes that consist, e.g., of a mix of desert dust and urban pollution. We tested the channel for the complex situation of East Asian pollution. We find good agreement of the inferred mineral-quartz-related backscatter coefficient to results obtained with another mineral quartz channel which was operated at 546 nm (primary emission wavelength at 532 nm), the functionality of which has already been shown for a lidar system in Tsukuba (Japan). The advantage of the novel channel is that it provides a better signal-to-noise ratio because of the shorter measurement wavelength.

Asian dust event observed in Seoul, Korea, during 29-31 May 2008: analysis of transport and vertical distribution of dust particles from lidar and surface measurements.

In this study, we investigate the transport of dust particles, its vertical distribution, and the associated meteorological conditions during an Asian dust event that was observed in Seoul, Korea on May 29-31, 2008. This study analyzes data from ground-based and space-borne 2-wavelength polarization lidars, particulate mass concentrations, and synoptic weather data. Surface meteorological station observations of dust phenomena, dust transport model, and weather maps consistently show that the dust particles were transported from the source regions (Inner Mongolia, Man-Ju, and Ordos areas) to Korea via the northeastern part of China. Network observations of the PM(10) concentrations in Korea revealed that a majority of the heavy dust particles traveled across South Korea from the northwest to the southeast direction with a horizontal scale of 250-300km and a traveling speed of approximately 40kmh(-1). This extraordinary dust event, in terms of its intensity and timing during the year, occurred due to the blockage of an unusually intensified low-pressure system in the northeastern part of China as well as high-pressure system centered over the Sea of Okhotsk and the Kuril Islands. The low values of the particle depolarization ratio (delta(532)) (

Characteristics of aerosol optical properties in pollution and Asian dust episodes over Beijing, China.

Aerosol optical properties were continuously measured with the National Institute for Environmental Studies (NIES) compact Raman lidar over Beijing, China, from 15 to 31 December 2007. The results indicated that in a moderate pollution episode, the averaged aerosol extinction below 1 km height was 0.39+/-0.15 km(-1) and the lidar ratio was 60.8+/-13.5 sr; in heavy pollution episode, they were 1.97+/-0.91 km(-1) and 43.7+/-8.3 sr; in an Asian dust episode, they were 0.33+/-0.11 km(-1) and 38.3+/-9.8 sr. The total depolarization ratio was mostly below 10% in the pollution episode, whereas it was larger than 20% in the Asian dust episode. The distinct characteristics of aerosol optical properties in moderate and heavy pollution episodes were attributed to the difference in air mass trajectory and the ambient atmospheric conditions such as relative humidity.

Characteristics of dust aerosols inferred from lidar depolarization measurements at two wavelengths.

Lidar depolarization measurements were performed simultaneously at two wavelengths (532 and 1064 nm) in an Asian dust event. The observed particle depolarization ratio for 1064 nm was generally larger than that for 532 nm, and it was found that the mixing of Asian dust and other spherical aerosols must be taken into account. A simple two-component theory considering two types of aerosol (dust and spherical aerosols) was developed and applied to the observed data. The mixing ratio of dust and the backscatter-related Angström exponents for dust and spherical aerosols was derived. These parameters can be used to infer characteristics of the aerosols and the mixed states.

Algorithm improvement and validation of National Institute for Environmental Studies ozone differential absorption lidar at the Tsukuba Network for Detection of Stratospheric Change complementary station.

Recently, a data processing and retrieval algorithm (version 2) for ozone, aerosol, and temperature lidar measurements was developed for an ozone lidar system at the National Institute for Environmental Studies (NIES) in Tsukuba (36 degrees N,140 degrees E), Japan. A method for obtaining the aerosol boundary altitude and the aerosol extinction-to-backscatter ratio in the version 2 algorithm enables a more accurate determination of the vertical profiles of aerosols and a more accurate correction of the systematic errors caused by aerosols in the vertical profile of ozone. Improvements in signal processing are incorporated for the correction of systematic errors such as the signal-induced noise and the dead-time effect. The mean vertical ozone profiles of the NIES ozone lidar were compared with those of the Stratospheric Aerosol and Gas Experiment II (SAGE II); they agreed well within a 5% relative difference in the 20-40 km altitude range and within 10% up to 45 km. The long-term variations in the NIES ozone lidar also showed good coincidence with the ozonesonde and SAGE II at 20, 25, 30, and 35 km. The temperatures retrieved from the NIES ozone lidar and those given by the National Center for Environmental Prediction agreed within 7 K in the 35-50 km range.

Influence of atmospheric and system parameters on multiple scattering in spaceborne backscatter lidar measurements.

We have simulated backscatter signals of spaceborne lidar systems with the help of a Monte Carlo model. Calculations were performed for various combinations of system parameters. As typical examples of atmospheric observation targets, two kinds of cirrus cloud and two kinds of aerosol were considered. Both total multiple scattering and the significance of individual higher scattering orders are discussed. For all cases, an approximate multiple scattering factor F was calculated that can be used to correct the single-scattering lidar equation to account also for multiple scattering.

Estimation of quartz concentration in the tropospheric mineral aerosols using combined Raman and high-spectral-resolution lidars.

A remote sensing method is presented that enables the determination of quartz concentration in mineral aerosols from simultaneously measured, high-spectral-resolution lidar and quartz Raman lidar signals.

Extinction-to-backscatter ratio of Asian dust observed with high-spectral-resolution lidar and Raman lidar.

Extinction-to-backscatter ratio or lidar ratio is a key parameter in the issue of backscatter-lidar inversions. The lidar ratio of Asian dust was observed with a high-spectral-resolution lidar and a combined Raman elastic-backscatter lidar during the springs of 1998 and 1999. The measured values range from 42 to55 sr in most cases, with a mean of 51 sr. These values are significantly larger than those predicted by the Mie computations that incorporate measured Asian dust size distributions and a range of refractive index with a typical value of 1.55-0.005i. The enhancement of lidar ratio is mostly due to the nonsphericity of dust particles, as indicated by the T-matrix calculations for spheroid particles and a number of other theoretical studies. In addition, possible contamination of urban aerosols may also contribute somewhat in optically thin cases. Mie theory, although it can well describe spherical particle scattering, will not be sufficient to represent the scattering characteristics of irregular particles such as Asian dust, especially in directions larger than approximately 90 degrees when the size parameter is large.