Recently, a team from the Fraunhofer Institute of Laser Technology (ILT) and the Leibniz Institute of Atmospheric Physics (IAP) in Germany has developed a portable lidar system that can move independently. Such systems can be produced on a large scale and combined into an operational network to provide real-time high-quality data of temperature and wind speed for climate research.
Today, whether it is to make weather forecast, build climate model or arrange rocket launch, it needs accurate data about the atmosphere as support. Scientists can obtain these data by using a laser radar (laser detection and ranging) system to send a laser beam into the sky. The backscattered light can be used to calculate wind and temperature data up to 100 km high.
After the laser radar system sends beams through the atmosphere to an altitude of more than 100 kilometers, these beams usually pass through three layers: the troposphere (about 15 kilometers high), the stratosphere (about 50 kilometers high) and the middle layer (about 90 kilometers high). The height of these layers mainly depends on the solar radiation, but also changes with the seasons or geographical location.
In this process, the laser beam emitted by the laser radar excites the atoms in the atmosphere (such as potassium or iron), and then the particles reflect the light back, forming a scattering effect. Then, the telescope in the lidar system on the earth will catch the backscattered light. From the spectrum, variables such as temperature and wind speed can be derived. The measurement height is determined by the transmission time of the laser pulse, and the concentration of particles at the height is determined by the number of special photons.
Through the lidar and radar system, the ground team can accurately measure the movement in the atmosphere. One of the advantages of the fixed lidar system as a measuring method is that it can measure the current almost indefinitely along the laser beam.
The ground laser irradiates various atoms or aerosols in the atmosphere and scatters back a single photon. However, the biggest challenge for laser engineers is actually resonance scattering.
In May and November 2022, the latest generation of lasers was installed in two lidar systems of Kuhlungsborn, and the measurement of the height of up to 100 kilometers has been demonstrated. This work is funded by the "VAHCOLI" (vertical and horizontal lidar coverage) project, which focuses on exploring the atmosphere in vertical and horizontal directions.
This is achieved by directing a laser to four telescopes with a tilt of 30 °. There are four such lidar systems in the network, which can measure 10000 square kilometers in the sky. This is by far the most modern and powerful mid-atmosphere lidar system in the world. Researchers have optimized the emerald lasers in the laboratory, so they can run for thousands of hours in LIDAR system without maintenance or adjustment.
The research team has planned several general directions on how to further develop this technology. The project has 10 partners and will be launched in June 2023 as part of the RUBIN funding plan.
This scientific work is being promoted with the EULIAA (European Atmospheric Climate Monitoring Laser Radar Array) project launched in January 2023. Laser physicists plan to install a crystal to convert the laser radiation in the laser resonator into a wavelength of 386 nm. It uses Fraunhofer line with low photovoltaic background, which can measure iron atoms. So far, this can only be achieved through a much less efficient external frequency doubling. The preliminary test is very promising.
In addition, the research team will establish two new lidar systems in 2023, which will ensure that seven partners from five countries can collect climate data with unprecedented quality in areas more than 10 kilometers where there is currently no data.
Their next goal is to integrate the lidar data into the European database in real time. These data will be used for weather forecast and climate model, because this lidar system can measure the wind and temperature distribution at an altitude of more than 10-50 kilometers in real time day and night. The system also provides relevant data for rocket launch. In the long run, satellite-based laser radar is also conceivable. In projects such as the MERLIN mission, Aachen partners have acquired a large number of satellite-based laser technologies.
The importance of this work is reflected in the study of climate change in the middle atmosphere, which has been rarely studied so far. Researchers hope that the new system can be used to continuously observe changes in a wider range, which will have a significant impact on long-term climate prediction.
From June 27-30, 2023, Fraunhofer ILT will introduce and demonstrate this development and the breakthrough application of these technologies.
Source: OFweek
