Research On Scattering Spectrum Measurement Method Based On Photon Correlation Spectroscopy Technology

Turbulent motion plays an important role in the formation of weather and climate.The generation and development of turbulence are highly disordered and random,and its influence on the intensity of atmospheric turbulence motion and space-time structure factors is more complicated.Temperature pulsation is one of the most important physical quantities in the parameters describing turbulence,and the accuracy and precision of its data detection directly affect the acquisition of sensible heat and latent heat flux.Temperature fluctuation refers to the superposition of small temperature changes in atmospheric temperature in a short period of time.At present,for the detection methods of atmospheric temperature fluctuation data,ultrasonic temperature difference anemometer and platinum wire temperature pulsation instrument have been widely used in direct measurement of turbulent flux due to their short response time.However,when the above-mentioned fast-response equipment is used to measure single-point temperature fluctuations,the detection height is limited to a certain extent.When the air probe equipped with high-response and high-sensitivity temperature measurement equipment such as a temperature pulsator is used to detect atmospheric temperature pulsation profiles,the detection time is longer,and the mass of the air probe is small,resulting in wind interference at high altitudes.The discreteness of the measured data is relatively large.This thesis proposes a method for detecting temperature fluctuations based on photon correlation spectroscopy.The essence of temperature fluctuations is caused by the instantaneous changes in the average velocity of molecular thermal motion.Because in the atmosphere,the molecules are collided by different surrounding media to produce Brownian motion,which makes the frequency of molecular scattered light produce a Doppler shift relative to the frequency of incident light.Macroscopically,the scattered light intensity fluctuates with time under a certain scattering angle.Fluctuating.By measuring the intensity of the scattered light signal that changes instantaneously,information about the instantaneous change in the average velocity of the Brownian heat motion of the measured gas molecules can be obtained.In order to verify the feasibility of measuring the scattering spectrum by photon correlation spectroscopy,the thesis starts from the theory of photon correlation spectroscopy,and obtains the relationship between the normalized time autocorrelation function of the scattered light intensity and the Rayleigh scattering spectrum width based on the characteristics of Brownian motion.The signal simulation method of wavelet transform is used to simulate the scattering signal of particles,which verifies the feasibility of the theory and the inversion algorithm.A photon correlation spectrum measurement system is built,which is mainly composed of a light source,incident and scattered light paths,photomultiplier tubes,amplifiers,photon counters and digital correlators.The accuracy of the experimental system was calibrated by measuring the particle size of ultrafine particles.Finally,the Rayleigh scattering spectrum width at different temperatures was measured by the atmospheric simulation calibration box,and the error analysis was carried out with the theory,which finally proved the feasibility of the detection method based on photon correlation spectroscopy.It lays the foundation for the subsequent detection of the temperature fluctuation profile of the boundary layer.