Design And Application Of Distributed Optical Fiber Raman Temperature Measurement System For Ice Detection

In ice science research,ice cover thickness is one of the most important indicators for monitoring ice flood disasters.And it is also an important parameter for calculating the force of ice on hydraulic structures.The profile temperature of ice cover is one of the key factors reflecting the growing and melting processes of ice cover and plays an important role in monitoring the changes of ice cover thickness.Therefore,it is of great significance to study the measurement methods and techniques of the profile temperature to accurately identify each interface,timely acquisition of thickness,and thermodynamics changes inside the ice cover.At present,the traditional measurement method of ice cover temperature can measure the ice temperature information in a small local area.Facing the demand of long distance temperature measurement,there are disadvantages such as high layout and maintenance costs and vulnerability to interference.Distributed optical fiber sensing technology uses ordinary optical fiber as the sensitive medium and transmission medium.The temperature information at any point along the sensing fiber can be detected.Compared with the traditional temperature measurement method,it has high accuracy,long measuring distance and anti-interference.Aiming at the deficiencies of large-scale temperature detection methods in ice environment,this paper has designed a distributed optical fiber Raman temperature measurement system that can be used for ice conditions detection.To improve the spatial resolution without upgrading the hardware of the existing temperature measurement system,a deconvolution correction algorithm based on frequency domain demodulation is proposed to avoid the inaccurate temperature measurement caused by the limited bandwidth of the system.On this basis,a temperature measurement device with high vertical resolution was designed,which is helpful for a more detailed observation of the changes in the ice cover temperature of rivers and lakes during the growing and melting processes.This article mainly completed the following aspects of work:(1)Based on the basic principle of distributed optical fiber Raman temperature measurement system,the temperature measurement principle based on the temperature sensitive characteristics of optical fiber Raman scattering and the positioning principle based on optical time-domain reflection technology are studied.The advantages and disadvantages of two commonly used temperature demodulation methods are analyzed.And the dual-channel demodulation method based on Raman Stokes scattering light is selected;(2)The overall design scheme of the system is determined,and the system experimental platform is built according to the selected system modules.Aiming at the problem of weak signal intensity and low signal-to-noise ratio of Raman scattering signal,16000 times cumulative average and wavelet modulus maxima algorithm are used for denoising.Aiming at the attenuation of Raman scattering signal in the propagation process,the method of signal attenuation compensation is used for correction.Besides,the fitting curve of temperature and Raman ratio was obtained by temperature calibration experiment,and the fitting coefficient R~2was 0.9994;(3)Related experiments were carried out to obtain the performance parameters of the system.The results show that within the measurement range of 2 km,the system has good temporal and spatial repeatability,the spatial resolution is 1.3 m,and the temperature measurement accuracy is±0.5℃.To solve the insufficient spatial resolution of the system,a deconvolution correction algorithm is proposed.The spatial resolution is increased to 0.5 m,and the maximum temperature measurement error is 0.48℃.(4)A vertical high-resolution temperature measurement device was designed,which vertical resolution was 2.5 mm.The detection experiment of profile temperature during the growing and melting processes was completed.The experimental results show that the device can accurately identify the change of ice cover thickness,so as to achieve the purpose of identifying the ice cover thickness.