Design And Implementation Of Holographic Droplet Spectrometer

Clouds have an impact on the radiative transfer of electromagnetic energy within the atmosphere and play a key role in regulating climate change in the Earth’s atmosphere.Direct observational studies of cloud production and extinction processes are of great importance for the development of cloud microphysical parameterization schemes in numerical weather prediction(NWP)models.Direct observation of cloud microphysical properties is quite complex and difficult,and there are huge differences between the cloud microphysical parameters obtained from direct observations and the output of NWP models.The paper designs a holographic droplet spectrometer based on coaxial digital holographic interference technology.As a non-contact,weakly interfering optical cloud detection instrument,the holographic droplet spectrometer has the advantages of real-time observation of cloud weather processes,high spatial and temporal resolution,and continuous long-time observation,and is an important instrument for accurate acquisition of cloud particle size and three-dimensional spatial distribution.It can provide data support for NWP model construction,cloud microphysical parameterization scheme,and artificially influenced weather research.Firstly,the existing cloud observation devices at home and abroad are analyzed.The in situ atmospheric cloud particle detection instrument based on holographic interference technology can observe cloud droplets with diameters of 10 μm and above,and after further integration of the optical imaging system,the observed minimum cloud particle diameter is increased to 6.5μm,and the minimum diameter of cloud particles is 2 μm,so the complete spectral distribution of cloud particles still cannot be obtained.The cloud observation instrument FM-120 based on the light scattering principle adopts the inhalation measurement method,which destroys the three-dimensional spatial distribution of cloud particles but improves the observation scale of cloud particles to 2-50 μm and can provide the complete spectral distribution.The holographic fog droplet spectrometer designed in the thesis uses digital holographic interference technology to extend the minimum observation diameter of particles to 2-100 μm by adding an optical imaging amplification system in front of the camera with an optical magnification of 5.89 times and a combined recognition rate of 98%for different particle sizes,and a system sampling frequency of 10 Hz.The system uses a pulsed laser as the light source with a pulse width of 300 ns,and the camera uses The maximum displacement of the particle velocity in 0-10 m/s is 0.52μm,which can effectively eliminate the particle trailing phenomenon.The shape structure designed for the core optical path structure,the use of streamlined protective cover,the wind direction can be rotated with the wind following the mechanism can effectively avoid the impact of the components generated by the Carmen vortex street phenomenon on the sampling area flow field distribution.For the instrument to work in a high humidity environment,the instrument is vacuumed and filled with nitrogen,waterproof coating and other sealed waterproof design.The designed structure was subjected to finite element analysis for flow field,thermal,stress and low frequency vibration,and the structure was optimized according to the analysis results.The holographic fog-drop spectrometer online software was designed to be able to display the observed cloud microphysical characteristics parameters.The holographic droplet spectrometer was calibrated by the resolution plate,and the data observed by FM-120 and holographic droplet spectrometer were compared in the cloud chamber test,and the results showed that the measurement results of the two instruments on cloud droplets were in good agreement.Finally,the holographic droplet spectrometer was validated in the field and continuous cloud observation was carried out at the Liupanshan Topographic Cloud Field Science Experiment Base,and the test results showed that the observation results of the two instruments were in good agreement.The correlation between cloud microphysical parameters in the process of cloud generation and dissipation was analyzed by the observation data.