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.
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.
Surface atmosphere has the small and steep spatiotemporal dynamics. It is influenced by the ground / sea-surface conditions, their up and down, air current, and so on. It greatly affects to the human living space. 265nm LED mini-lidar is developed to observe the surface atmosphere. As the transmitting light is in solar blind region, it can monitor near-range atmosphere up to 100m in daytime with the same signal-to-noise ratio in nighttime.
The lidar echo detection was evaluated under the solar illumination. It is confirmed that the enough signal-to-noise ratio is obtained in daytime, which is matched with the theoretical estimation. The surface atmosphere observation is simulated with the artificial fog / rain facility “Light Tunnel”. Fog flow and rainfall were visualized and analyzed with time series lidar echoes. We will propose the easy-to-use method for dynamics monitoring of surface atmosphere.
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