Light detection and ranging (lidar) have been valuable tools in remote sensing of aerosols near the ground. For the operation of a lidar system, the laser, as a transmitter, plays a vital role in the whole system. Laser Diodes (LD) and Diode-Pumped Solid State (DPSS) laser technology have evolved, making the lidar system more compact compared to Nd:YAG laser sources. However, the lidar system’s long time and continual operation need maintenance to keep the laser source output stable. Also, the laser source is vulnerable to static electricity and needs to stabilize electric power. In this work, a multiwavelength lidar system with a Light Emitting Diode (LED)-based light source is designed and developed to monitor aerosol distribution in the near-ground atmosphere during continuous observation. The LED light source does not require any heat dissipation system and can emit light for long periods with constant output. The LED lamp light sources with wavelengths of 365, 450, 525, and 630 nm (peak power of up to 2W) are used as lidar transmitters. This lidar system visualizes rapid activities of aerosols in the near-range measurement due to its repetition frequency of over 250 kHz. Analysis of the backscattering light intensity with four wavelengths from this LED lidar system produces real time extinction coefficient and size distribution in the near-ground atmosphere. This report discusses the design and practical test of the multi-wavelength LED Lidar.
Visualization of the wind field in the lower atmosphere and its dynamics are important for understanding the mixing and interaction between geology and atmosphere. The dispersion of that dust is a major problem not only for environmental protection, but also for human health, such as respiratory diseases, and air pollution caused by man-made dust in urban areas, so great demands for visualization and monitoring of wind fields and dust flow near the ground surface are raised. To observe atmospheric flows on small spatio-temporal scales near ground, we are developing a low coherence Doppler lidar. Low coherence Doppler lidars can capture the dynamics of the lower atmosphere because of the high spatial and temporal resolutions of 1 m and 5 ms, respectively. Dust flow measurements can be made, while the system is not sensitive enough to measure the atmospheric wind itself. That is current task. In this paper, we discuss the efficiency improvements of the lidar transmitting and receiving optical systems and the receiving system itself of fiber coupling by two orders of intensity with a fiber-type distributed feedback laser diode. The beam quality of this light source was higher than the previous bulk type one, and the interference light intensity was six times higher. The Doppler shift frequency measurement with a rotating target showed a larger signal-to-noise ratio of approximately 70 dB, 30dB higher than the previously reported system.
In this work, we propose a low-coherence Doppler lidar (LCDL) to measure particle velocity at near-surface atmosphere. To measure particle velocity information at near-surface atmosphere, it is necessary to conduct the measurement at high frequency and resolution. Low coherence light source can satisfy this high-resolution criterion. We discuss the system efficiency to detect atmospheric echoes by theoretical analysis. In the particle velocity experiment, Doppler shifted frequency is about 5 MHz and the particle velocity calculated from the peak Doppler signal is 2.7 m/s, while minimum and maximum velocity are 1.85 and 2.92 m/s, respectively. Anemometer result shows good agreement with LCDL results.
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