Sea fog weather11/14/2023 ![]() Hence, the SNSPD with a substrate of MgF 2 has a better performance and a higher detection rate. Compared with a Si substrate, the MgF 2 is more compatible with the NbN lattice constants and has a greater thermal conductivity. The NbN energy gap is 5.12 meV, which is much smaller than the photon energy (1 eV) therefore, the 100-nm wide nanowires have high detection efficiency in the infrared band. The SNSPD critical temperature is 8.5 K, the critical current is 7.5 \(\mu \)A, and the photosensitive area is 10 \(\mu \)m * 10 \(\mu \)m. We also fabricated Au electrode and optical resonant cavity on SNSPD. We used MgF 2 as the substrate to grow the NbN film with a size of 5 nm and the nanowires were created using electron beam lithography (EBL). The preparations for operating the SNSPD consisted of NbN film growth, nanowire preparation, electrode growth, optical resonator growth, packaging, testing, etc. The automatic control system of the SNSPD consists of an optical coupling system, a cooling system, an output circuit, and a display control system. Hence, the detected particle density can be derived from the strength of the echo signal as follows: \(\beta \)( \(\lambda \), R)indicates that the intensity of the echo signal is proportional to the backscattering cross section and density of the particle being detected. The distribution and range of the fog are calculated and the results show that the SNSPD proved capable to detect this long-distance meteorological phenomenon.Īccording to Lidar theory, the particle scattering follows the Mie scattering theory when the incident wavelength \(\lambda \) is much smaller than the radius r of the detected particle ( i.e., \((i\mathrm(\lambda )\), in which \(\sigma \)( \(\lambda \)) is the backscattering cross section for a detected particle, cm 2 sr −1 and N(R) is the detected particle density, cm −3. In this study, SNSPD is used to explore the influence of the distance to the fog on the echo signal rate. Therefore, the high efficiency, low noise SNSPD system has obvious advantages for long-distance sea fog detection. In the detection of remote atmospheric particles, the echo signal is extremely weak and the detector signal to noise ratio requirement is extremely high. But to date, the technology has not been applied to sea fog measurements. SNSPD has been applied to distance measurements based on a satellite laser system 16, 17. The detection efficiency is up to 93% in the near infrared band while the dark count is less than 100 Hz. ![]() ![]() SNSPD is a new type of single photon detector 7, 8, 9, 10, 11, 12, 13 with high detection efficiency, low dark count, fast detection rate, high sensitivity, wide response spectrum, and other advantageous features 14, 15. Thus, traditional Lidar for weather prediction was around twenty kilometer range. The infrared detection efficiency is often less than 30% and the dark counts are a few kHz 6. In order to improve the detection rate, active, passive, gate pulse suppression, and other methods are used for self-sustaining avalanche quenching. Laser photon radar based on single photon detectors is used to detect the range and concentration of clouds, humidity, wind fields, air pollution, pollutant diffusion, and to provide weather forecasts 2, 3.Īt present, the single photon detectors used in lidar weather prediction are mainly InGaAs/InP avalanche photodiodes operated in the Geiger mode 4, 5. Laser weather radar 1 is a commonly used sea fog detection technology with excellent azimuth accuracy, distance resolution, and high-quality, low background noise. Sea fog is a common phenomenon of sea weather and has a significant impact on fisheries, navigation, and flight safety. Therefore, the capability of this SNSPD-based Lidar was close to the theoretical limit for sea fog measurements for extremely high signal-to-noise ratio of SNSPD. The height of the sea fog is about two hundred meter while the visibility at this height is about 90 km due to the Earth’s radius of curvature. Then the fog concentration and the velocity of the fog were deduced from the distribution, which is consistent with the weather prediction. The fog echo signal distribution in the range of 42.3 ∼63.5 km and 53.2 ∼74.2 km was obtained by the Lidar system. The system, which was verified by using a benchmark distance measurement of a known island, is applied to the Mie scattering weather prediction Lidar system. We demonstrated a Long-distance Lidar for sea fog with superconducting nanowire single-photon detector (SNSPD), which extended the ranging area to a 180-km diameter area. ![]() Remote sensing through laser is an effective tool for monitoring sea fogs, but still challengeable for large distance. The monitor of sea fogs become more important with the rapid development of marine activities.
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