Research On 3-D Cloud Reconstruction Algorithm Based On DPC Data

Cloud is a mixed colloid composed by water droplets and ice crystals in atmosphere.It occupies above 60% of Earth surface.Because of huge coverage area,it plays a key role in radiant energy balance of earth and climate evolution.Therefore,cloud remote sensing has great significance for research of earth environment.In the past,due to limitation of observation instrument,most of cloud research stay on 2-D plane.3-D cloud structures are not considered in those studies.However,position and structure of clouds have a great influence on accuracy of atmospheric radiation transmission in atmosphere.2-D cloud information obtained from single-angle sensor often ignores impact of 3-D cloud morphology on final observation results.Above all,reconstruction of 3-D cloud structure from multi-angle data is necessary to improve accuracy of visualization of cloud property.GF-5 satellite is lunched in China on May 9,2018.The DPC sensor of it provided polarized information with multi-angle and multi-spectral characteristics.Based on DPC data,we explore 3-D structure reconstruction and visualization property of cloud in this paper.We analyzed relationship between the sensor position,true cloud position and cloud projection position during observation process of DPC.After this process,the ray casting equation along observation path could been obtained from observation angle information and channel spectrum information of all pixels.We define interval and range of resampling to convert formula solution of equation into numerical solution in 3-D visualized grid space.Finally,distance threshold method(DTH)is used to summarize relationship between observation information of different observation angles.We can achieve 3-D reconstruction structure of cloud.In terms of 3-D cloud reconstruction verification,we extract a profile section of 3-D reconstruction structure and compared it with Vertical Feature Mask(VFM)and cloud layer products of CloudAerosol Lidar with Orthogonal Polarization(CALIOP)data.Those comparisons illustrate reliability of our algorithm from quantitative and qualitative perspective.Different accuracy of reconstruction results for different types of clouds show different structure feature.In addition,the most important application of 3-D cloud structure is expression of cloud property.In this paper,confidence and phase of cloud are visualization in 3-D space.We combined it with 2-D cloud property and VFM of CALIOP in the same area to analyze influence of cloud structure on property of cloud edge area.The advantages of 3-D cloud property expression are illustrated.This structure can provide carriers for determine role of cloud in interaction between clouds and other components in atmosphere.It also can take a scientific reference for 3-D structural characterization of aerosols in near future.The 3-D cloud structure reconstruction and property visualization algorithms make up for lack of application of passive optical remote sensing data in 3-D space.It also provides better carriers for expression of cloud property.This algorithm would become basement for improving utilization and application fields of DPC data in near future.At the same time,it also provides help for study of influence of 3-D cloud structure on radiation transmission in cloudy atmosphere and the interact relationship between the clouds and other atmospheric components.We may provide a new idea for utilization of multi-angle polarized remote sensing satellite data in this paper.