Research On Cirrus Cloud Parameters Based On Ground-based Variable Field Solar Photometer

Solar photometers of single field view can be used to measure characteristics of atmospheric aerosol particle.Some bands of Solar photometers can also be used to invert atmospheric precipitation and absorption gas content as well as cloud-related optical parameters.It is widely used in atmosphere observation networks to measure aerosol particles and precipitation.Solar photometer has great significance on environmental monitoring,optoelectronic engineering applications and satellite remote sensing inversion.Solar photometeris mainly used to measure aerosol optical properties in a cloudless atmosphere by using a combination of astronomical coarse tracking and four-quadrant fine tracking.There are often thin clouds(such as thin cirrus clouds)in measurement pathand the four-quadrant fine-tracking is susceptible to interference when there are non-uniform clouds,which affects accurate measurement of optical properties of aerosol particles.By comparing scattering phase functions of aerosol particles,water clouds and cirrus clouds,it is shown that cirrus clouds show a very large peak near 0°.The scattering radiation intensity of cirrus clouds varies sharply from that of aerosol particles and water clouds in the forward angle of 5°.Therefore,a variable field photometer based on image tracking is considered which can accurately measure solar radiation in fields of view of 0.8°,2°and 5° in all weather.Cirrus clouds,aerosol particles,and water clouds were distinguished by solar radiation ratiosin different fields of view.At the same time,it is considered to compare the scattering radiation in different forward angles of different mediums which can provide reference for detection of optical properties of aerosols and cirrus clouds.The main work of this paper is as follows:1)The relationship between transmission radiation and cloud particle size,optical thickness was studied when thin cirrus clouds existed by software,which calculated the solar transmission radiation in 0.4?2.5?m band.It provides theoretical guidance for the design of instrument for measuring transmission radiation in cirrus cloud.2)The transmittance and scattering ratios of aerosols,water clouds and cirrus clouds at different angles in the forward direction were simulated and calculated by using DISORT.It is found that the total transmission flux ratio of cirrus clouds in the small-angle field of view is much higher than that of aerosol particles and water clouds.The scattering ratio of large particle is smaller than that of small particle,which can be used to determine current particle size,which provides a theoretical basis for the use of ground-based solar photometers to distinguish between cirrus clouds and aerosol particles.3)The principles of measuring solar radiation and the design principles of optical systems of several commonly used single-field solar photometers was introduces,which provided technical support for the development of a new type of variable field photometer based on image tracking.The instrument design and tracking system algorithm were introduced in detail.The experiment results show that the instrument has high tracking accuracy.4)The instrument was compared with the POMO2 sky radiometer after calibration by the Langley method in clear atmosphere.The comparison experiment was conducted in three different atmospheric environments with clear weather,water clouds and cirrus clouds.It is found that the transmission ratio measured by instrumentof cirrus clouds in different fields of view was larger than that of aerosol particles and water clouds.Combining the current atmospheric optical thickness and the Angstrom index of aerosols,the comparison of measured values of field-of-view scattering ratios with simulated values under different weathers indicates that the instrument has the ability to distinguish between cirrus clouds and aerosols,and can initially determine the size range of particles,which provides a technical means for ground-based remote sensing of cirrus clouds.