Study Of Optical Attenuation By Sand And Dust Systems At Different Relative Humidity

During the sandstorm passage,with the significant increase of dust concentration,the relative humidity also will be increased significantly.Both relative humidity and dust concentration have a strong attenuation effect on electromagnetic wave.Generally,the sand dust concentration and relative humidity change at the same time during the development of dust storms.How these two factors affect the scattering and absorption of electromagnetic waves simultaneously is still unclearly,and it is no experimental research.In this paper,we focus on the attenuation of light and near-infrared waves by sand and dust systems under the different relative humidity as following.Firstly,the attenuations of light waves with length 405 nm and 532 nm by sandstorm were studied on the roof of Qilian Building,Lanzhou University during the sandstorm in March 2021,while the environmental factors such as relative humidity,temperature and wind speed were experimentally monitored.The results indicated that the sand was uniformly distributed in local places within a short period of time,and when the wind speed increased in the local range,it was accompanied by the decrease of ambient temperature and the increase of ambient relative humidity,which led to the decrease of the wave power of the laser beam at the receiving end,and made the increase of attenuation coefficient,and vice versa.Secondly,an indoor experimental study on the attenuation of light(wavelength405 nm,532 nm)and near-infrared(NIR)waves(wavelength 850 nm,1064 nm,1550nm)by the sand and dust system under different of relative humidity was carried out,at three working conditions,humidified wind and sand particle system,sand particle system,and water vapor system.The results show that under high relative humidity conditions,the scattering and absorption of the light and NIR waves by sand particle system are significant at different temperatures.Under low relative humidity,the factor affecting the electromagnetic waves through the dust system is the dust concentration,and the relative humidity and temperature effect on the scattering and absorption of light and near-infrared waves can be ignored.At the same time,it is found that at the optical bands and near-infrared bands,the attenuation enhancement resulted from relative humidity is greater,when the wavelength is shorter,which can be described by the two parameter Kasten model.Finally,The "equivalent model" and "water-sand double-layer model" are used to calculate the attenuation of light wave and near-infrared wave by sand dust system under experimental conditions.The results show that the "water-sand double-layer model" should be used to study the attenuation of electromagnetic waves by dust particles when the relative humidity is greater than 60%.