Study On Scattering Features Of High Voltage Transmission Towers And Lines In High-resolution SAR Time Series Data Sets

Synthetic Aperture Radar(SAR)senses ground objects by transmitting microwaves,so as to obtain the back scattering from the target surface.It can be divided into ground-based SAR,airborne SAR,and space-borne SAR according to the carriers.Recently,space-borne SAR interferometry(InSAR)has rapidly developed into an important ground observation technologies due to its wide coverage,clouds penetrable and active imaging in all weather.What is more,high resolution space-borne SAR sensors can acquire images with a resolution of 0.5m to 1m.As the number of satellites increases rapidly,a large amount of high-resolution SAR images can be accumulated globally.InSAR is mainly used to generate DEM and deformation monitoring.With the development of high-resolution SAR satellite technology,the description of the shape and structure of ground objects has become more and more clear.Therefore,InSAR technology gradually has been applied into some special large-scale special artificial structure,such as transmission towers and lines.With the specific SAR azimuth and incident angle,the UHV tower cross-arms and trunk in the high-resolution SAR images are especially clear,and the trans-water transmission lines generate two strong elliptical scattering spots.How to explain these scattering features is particularly important for object recognition and deformation monitoring in SAR images.This paper selects two typical research targets in Wuhan,1000 k V transmission tower in the Wuhan UHV test base and 220 k V transmission lines across Yezhi Lake.We study high voltage transmission tower and lines scattering features in high-resolution SAR time series data combining with Lidar,and also explore the scattering feature of transmission tower with different icing thickness.This paper first analyzes the radar reflection geometric of artificial targets,including experimental tower cross-arm,the corner reflector,transmission towers and lines.Then,by extracting and comparing the maximum intensity,we analyze the scattering features of the experimental tower cross-arms with different icing thickness(uncovered,2?5cm and 8?10cm icing thickness)in Terra SAR Spotlight images;Secondly,combined with the three-dimensional point cloud data of the tower,we study the scattering and interferometric features of the UHV tower in the 1m Spotlight image.Using radar geometric projection and interferometric measurement methods,we separately extract the pixel number and interferometric phase difference in the scattering luminance region,and invert the height difference between the structures of the tower;Finally,we study the imaging geometry of the direct signal scattered spot of the transmission lines,and explore the effect of the line hanging on the position of the scattered spot.Through multi-phase SAR images time series analysis of the brightness and position changes,we study how the ambient temperature affects the line scattered spot position.This paper has the following research findings:1.Based on the ice-covering experimental of tower cross-arms,we find that the maximum scattering intensity of the tower is significantly attenuated when the ice thickness is 8?10cm,which is reduced by about 8d B.This indicates that the high-resolution spaceborne SAR is feasible to monitor the icing status of the tower.2.Multi-phase SAR intensity maps find that the scattering intensity of the tower cross-arms and trunk remained stable for a long time,and the variation is less than3 d B.Through the geometric imaging analysis of the tower steel structure in the SAR image,it can be seen that the tower scattering mechanism is mainly the dihedral reflection and the trihedral reflection composed of its own angle steel structure.Compared with the high-accuracy Lidar scanning results,we find that the inversion error of the height difference obtained by SAR interferometry is relatively lager,indicating that there are other factors affect the systematic error of the tower interferometric phase.3.SAR imaging geometry of the trans-water transmission line is similar to that of a bridge.The line scattered spot intensity of the direct signal is 60 d B,and the reflected signal is about 56 d B.It can be seen that after the reflection on the water surface,the radar signal scattering intensity loss is about 2.5 times,and the intensity fluctuates greatly because of water level.In addition,we have found and verified the characteristics of the direct reflection signal time series of the transmission line that is positively correlated with the ambient temperature,and has the reverse movement phenomenon with the water surface reflection signal in the azimuth direction of the SAR image.