Marine Radar Image Simulation Based On Scene Rendering

In maritime education and training,the flexibility of the radar simulator is greater than that of the real radar equipment and the cost is also lower,so the radar simulator is widely employed in the radar operation training.Presently,the algorithm commonly used in most domestic radar simulators to generate radar echo image is the scanningline intersection algorithm based on 2D coastline data.A major flaw of the algorithm is that the determination of the target occlusion relationship is unclear,thus the generated echo image is not realistic and the training quality is also reduced.To resolve the problems mentioned above,the author of the dissertation has carried out the research on radar image generation method based on 3D scene database,and the main research work includes is presented as below.1.Comparison between the working process of radar and the rendering process of 3D scene shows that there are many similarities between the two processes while there are also some obvious differences.On this basis,a radar image generation method based on scene rendering is proposed.The method involves perspective projection to render the scene.In other word,the z-Buffer algorithm put inside the graphics processor is used to solve the determination problem of the targets.To begin with,the radar detection range and echo intensity are calculated through the shader program of programmable graphic process unit(GPU).Further the calculation results are stored in the frame buffer and then read out and converted to radar radial scanninglines.Finally the scanninglines are mapped onto screen to generate radar echo image.When the projection is perspective,the foreshortening occurs,and the foreshortening makes the echo image interrupted.The image interruption is studied,the mitigation measure is proposed,and the bearing mapping error brought by multiple scanning lines generated by rendering at a time is analyzed.2.The dead-point&blind-point in the process of scanning conversion from polar coordinate to rectangular coordinate is analyzed,and a method using texture mapping to achieve scanning conversion is put forward.Instead of directly mapping scanninglines onto the screen,scanninglines are stored in a texture image.The circular radar echo display area is divided into a series of massive small sectors,then the texture image is mapped onto the small sectors to generate the radar echo image.The proposed texture mapping method combines the scanning conversion with the scene rendering process,as a result the scanning conversion is efficiently performed in GPU,and the dead-point&blind-point is overcame.3.To find a reasonable method for calculating the echo intensity,and the radar equations of isolated targets and extended targets are analyzed.On this basis,the radar equations suitable for radar image simulation are determined,and then an echo intensity algorithm based on the radar equations is proposed.The sinx/x function is adopted to analyze the directivity of the radar antenna.Further,a radar wave attenuation algorithm in the vertical direction is proposed,and the bearing extension&range extension of the echo and the side-lobe echoes are complemented by manipulating pixels in the texture image.The y constant model and empirical model are used to calculate the back scattering coefficients of targets.The experimental results of the simulation show that the reality of extended echo is noticeably improved,the echo intensity conforms to the characteristics of radar waves,and the effect of adjusting gain is more realistic.4.The basic method of building 3D radar database is presented.The database contains the data of terrain,port facilities,aids to navigation,vessels etc.Consequently,the built model is used in the simulation experiment.Experimental results show that the radar image of 360° circular scan is generated in about 3 seconds when the proposed scene rendering method is used.It fulfills the real-time performance requirements in the radar simulation,and the ship echo image changes with the ship size and orientation.The simulation radar image generated by scene rendering have the explicit occlusion effect,reasonable echo intensity and higher reality,it provides a better basis for the marniner’s radar operation training.