This PDF file contains the front matter associated with SPIE Proceedings Volume 13265, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Air pollution by particulate matters such as PM 2.5 has become a big problem about negative impact on the human body near the ground. Particulate matters activity follows wind flow and have a localized and complex distribution near the ground surface, depending on topography and structures on ground / sea surface. A Doppler Lidar is a useful method for wind measurement because the spatial distribution of wind can be obtained without disturbing the wind field, but monitoring near the ground requires high spatiotemporal resolution of a few meters and seconds. We have developed a Low Coherence Doppler Lidar (LCDL) with a high spatial resolution of 1m. Previous studies had been able to measure dust winds from dust dispersal but lacked the sensitivity to measure the winds themselves. To improve the sensitivity of the Lidar, the system was changed from a bistatic to a coaxial system. Compared to our previous setup, the sensitivity was improved by about 8 dB. Sensitivity was further improved by 10dB by devising the optical system. Calculating the SNR from the wind, it was estimated that the wind measurement would be sufficient within the 20 m measurement range.

This study investigates the Planetary Boundary Layer (PBL) dynamics over Taiwan’s complex terrain using vehicle-based Doppler Wind Lidar. The Taichung Basin and Yulin-Chiayi Plain are selected to employ the vehicle-based aerosol and wind lidars to measure the east-to-west cross-section of aerosol and wind of the PBL. The PBL cross-section observed over the Taichung basin and Yulin-Chiayi Plain indicated the significant changes in the PBL structure, including terrain-induced vertical mixing of aerosol, wind shear, and return flow of the local circulation. The results indicate the terrain-induced eddy causes significant convection in the lower boundary layers, promoting vertical mixing.

In this study, the estimation of Convective Boundary Layer Height (CBLH) using coherent Doppler lidar with a novel deep learning approach is presented. A modified stacked hourglass network, a convolutional neural network architecture is employed to automate the retrieval of CBLH from aerosol and wind products measured by the Doppler lidar. The model is trained using a comprehensive dataset collected over one year in central Taiwan, comprising over 30,000 lidar maps. Ground truth CBLH is determined from the variance of vertical velocity, and the dataset is divided into subsets to evaluate the minimum training requirements. The results demonstrate the effectiveness of the deep learning model in accurately predicting CBLH and the possibility of deriving CBLH from the aerosol backscatter profile.

LED mini-lidar has improved to observe the lower atmosphere and the surface atmosphere in daytime and nighttime with the same signal-to-noise ratio as the LED light source of DUV 265nm wavelength is installed. In this study, we discuss how small the optical power is required for the near range observation. The signal-to-noise ratio is controlled by the pulse repetition frequency and the accumulation time with the small transmitting optical power. As it is in solar blind area, it can be accomplished up to the detection limit of the lidar echo signal. We considered it experimentally and theoretically.

In the Fukushima Daiichi nuclear power plant accident, hydrogen gas was generated by the reaction of nuclear fuel with water, which caused an explosion and radioactive leakage. To prevent a recurrence, the reactor containment vessel is maintained under nitrogen gas. Lidar technology provides remote sensing with high spatial resolution. In this study, we aimed to investigate aerosol flow and nitrogen leakage using the developed compact Raman Lidar with a 355 nm 50 kHz DPSS laser. To demonstrate the system concept, we measured nitrogen gas artificially released at a flow rate of 10 NL/min at a distance of 10 m from the Lidar. The Lidar data were acquired with integration time of 20 s. Comparison of the data with and without nitrogen gas flow revealed that the system is capable of distinguishing the ambient concentration around 80% and the concentration of nearly 100% in the flow contained along the laser path inside a 1.5 m plastic tube. The reduction in oxygen concentration was also detected with another Raman channel.

This study explores the potential of Raman Lidar for measuring water vapor and water clusters generated by radiation ionization, addressing challenges in detecting radioactive isotopes in high radiation environments. The most common method for measuring alpha nuclide contaminants is to place a detector close to the contaminant and measure the alpha rays emitted. In this study, on the fundamental experiment, pure water particles were injected into a cubic glass chamber, and Raman signals for water (403.7 nm) and water vapor (407.8 nm) were detected for 355 nm incident light. A narrow bandpass filter (1.5 nm bandwidth) effectively distinguished between the Raman signals of water and water vapor. This led to the development of a three-channel Raman lidar capable of detecting nitrogen (387 nm), water (404 nm), and water vapor (408 nm). Measurements were conducted in a humidity-controlled environment using sealed Americium radiation sources at the Japan Atomic Energy Agency. Results showed that as radioactivity increased, water vapor signals decreased while water signals increased. It is expected that water values will rise at a rate of 7.5 times relative to the decrease in water vapor, with observed results indicating a change rate of approximately six times. Future work will focus on evaluating these change rates, improving measurement reproducibility, and estimating the diameter of water clusters.

Wind is one of fundamental meteorological elements describing the atmospheric state. Global wind observation is important to improve the initial conditions essential for numerical weather prediction and meteorological studies. A Doppler wind Lidar (DWL) is a promising approach for global wind profiling. We conduct feasibility study to realize global 4D wind observation from space. In the paper, we describe feasibility study of space-based DWL for future global wind profiling.

MOLI completed its management review and transitioned to the project phase-B in August 2024. MOLI utilizes a laser altimeter and an imager with the same optical reference to accurately measure canopy height and surface elevation. This will demonstrate the reduction of uncertainty in forest biomass estimation, which is related to canopy height. Additionally, it plans to improve the accuracy of surface elevation data in digital maps using the same data. The instruments will be mounted on the International Space Station (ISS) for observation. However, due to cost constraints and the ISS's limited lifespan, the challenge of developing the flight model within a short period must be addressed. We are responsible for developing the laser optical system and laser power supply. We will present the results of these studies to demonstrate the validity of the laser design for production.

Water vapor has been detected in the Martian atmosphere by multiple orbiting instruments. The Atmospheric Chemistry Suite (ACS) on the ExoMars Trace Gas Orbiter (TGO) observed H₂O mixing ratios rea ching up to 50 ppmv at altitudes of 100-120 km during global dust storms, while levels remained low (⪅2 ppmv) during other seasons. The Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft revealed that water transported to the upper atmosphere is dissociated by ions, producing atomic hydrogen that escapes into space, contributing to Mars’ water loss. This transport is seasonal, peaking in southern summer and intensifying during dust storms. Additionally, the Mars Reconnaissance Orbiter’s (MRO) imaging spectrometer detected hydrated minerals on slopes, suggesting that liquid water may intermittently flow on present-day Mars. However, an observational gap exists between high-altitude water vapor and surface water due to limitations in spatial resolution and a lack of measurements in the lower atmosphere. To address this gap, we propose using an airborne differential absorption lidar (DIAL) to search for water sources. DIAL provides high -resolution measurements both day and night, bridging the observational gap between high-altitude water vapor and surface water, thus enhancing our understanding of water transport and loss on Mars. Absorption lines of water vaporin the 2.7 μm and 1.8 μm bands have been selected in this study. Simulations show that both lines are capable of detecting water vapor sources with reasonable system parameters.

We have developed algorithms to produce JAXA ATLID level two products using data measured by the lidar ATLID and imager MSI onboard the EarthCARE satellite. The algorithms estimate particle optical properties such as extinction, backscatter, and depolarization ratio as well as layer identifier, particle type identifier, and planetary boundary layer height. Furthermore, the algorithm estimates extinction coefficient of four aerosol components, dust, sea-salt, carbonaceous, and water-soluble particles using ATLID data; the other algorithm uses both ATLID and MSI data to estimate the extinction coefficient of the four aerosol components and column-mean mode-radii of fine-mode and coarse-mode aerosols. Prior to the ATLID algorithm development, we have developed a similar aerosol component retrieval algorithm using CALIOP and MODIS data; this technique was introduced into the ATLID algorithm. These algorithms were applied to the CALIOP long-term data, and the estimates have been used for evaluating aerosol radiation effects and data assimilation.

Validation experiments for the EarthCARE ATLID JAXA Level 2a data products using the ground-based lidar network, the Asian Dust and aerosol lidar observation Network (AD-Net) are described. The ATLID JAXA level 2a standard data product consists of the feature mask, target mask, and optical parameters for aerosols and clouds, and planetary boundary layer height. The ATLID JAXA L2a research data product provides extinction coefficients for aerosol components (water soluble, mineral dust, sea salt, black carbon). Direct comparison with the ground-based 355-nm HSRLs and Raman lidars in AD-Net is the basic method for validating the standard data products for aerosol. A data matching method considering the trajectory of air mass is employed. Statistical comparison in the suitable temporal and spatial regions is employed in the validation of feature mask, target mask and cloud optical parameters, because the spatial distribution scale is small for clouds. In the validation of the research data product (extinction coefficients of aerosol components), multi-wavelength HSR and Raman lidars are employed because the aerosol components can be better estimated with more measurement parameters.

In addition to the manufacturing of earth observation satellites, TASA (Taiwan Space Agency) is also responsible for the education and promotion of satellite data and its applications. In recent years, by the growth of computing capacity and network transmission speed, the implementation of immersive technologies with virtual reality that blend the physical and virtual worlds easily allows users to enter the digital world and learn new things in the immersive environment.

We conducted demonstration experiment to observe sand and fog dynamics of particles with different sizes and material profiles by using the LED mini-lidar that meets the size and power consumption which will be mounted on Mars rover. We took field measurement of sand dust on Tottori Sand Dunes in Japan and observed its dispersion, and fog flow dynamics was observed in lab experiments by using this LED mini-lidar. These measurement results revealed that there are differences in the unique behavior of particle flow dynamics due to substance specification.

Ordinary Lidars can observe as far away as several kilometers, however they cannot observe shot distance objects. The atmosphere near the ground is affected by the inequalities of ground, and they move very fast and complicatedly. To measure the low and surface atmosphere even during the daytime, we have developed a short range mini-Lidar using a deep ultraviolet LED with peak wavelength of 265 nm. Because sunlight falling on the ground does not contain light near 265 nm, the atmosphere can be observed in daytime with this mini-Lidar. This mini-lidar have a deep ultraviolet LED with a peak power of 50 mW and a repetition rate of 1 MHz. It can observe atmospheric echoes up to 100 m in the open air during the daytime. We report the concrete fabrication of this 265 nm LED based mini-Lidar and the measurements of short-range atmosphere during adverse weather condition. The developed mini-lidar was quite small (150 mm cube) and light weight (1.6 kg) enough to carried by hand. Artificial rain and fog measurements were carried in our experimental facility “Light Tunnel” under various adverse weather conditions (rain: 30 – 80 mm/h, fog: visibility under 10 m over a distance of 100 m). We clearly observed the rainfall amount in accordance with transmittance. We measured time variations of fog flow and its shading of density. On-site observations of the low and surface atmosphere with this 265 nm mini-Lidar were carried. Their airflow dynamics and activities are discussed.

Traffic and health hazards caused by fog and smoke have become a societal problem. Capturing such phenomena in the early stages of their occurrence is expected to be useful for hazard countermeasures and safety planning. The objective of this research is to design and develop a mini-Lidar for atmospheric measurement using a 405 nm LD as a light source with a distance resolution and time acquisition of 0.15 m and 2s, respectively. Specifically, it aims to visualize the initial behavior of fog and smoke in the observation area, and to compare and evaluate the temporal changes of Lidar echoes and transmittance measurements. In the experiment, fog and smoke were generated in a 1m³ chamber positioned 15m away from the Lidar system. A transmittance meter is located at the chamber to visualize and quantitatively evaluate the initial behavior of the fog. It was found that there was a negative linear correlation between transmittance and Lidar counts in the range of transmittance above 90%, which is close to the initial fog density. Furthermore, in the correlation graph between Lidar counts and transmittance, the difference in slopes between fog and smoke indicates that there is a difference in the attenuation of light in each material. We also discussed it under the consideration of each of their extinction coefficients.

We present a 2 μm Differential Absorption Lidar (DIAL) system with a Superconducting Nanostrip Single-Photon Detector (SNSPD) for measuring water vapor. The SNSPD is particularly suited for DIAL applications owing to its superior characteristics such as high detection efficiency, low dark count rate, high photon count rate, and low timing jitter. In this paper, we report on the evaluation results of the System Detection Efficiency (SDE) and dark count rate of a SNSPD developed at National Institute of Information and Communications Technology and a demonstration of CO₂ measurement using a gas cell and a 2 μm tunable laser. At a detector temperature of 2.1 K, the SNSPD achieved a SDE of 70.5%. Furthermore, we directly observed the absorption spectra around the CO₂ R30 absorption line. Our results indicate that SNSPDs are a promising technology for 2 μm gas remote sensing applications.