Research On Ground Target Geo-location Technology Based On Digital Elecation Model For High-altitude Long-range Aerial Camera

The high-altitude long-range aerial camera,as one of the main equipment that obtains the remote sensing image of the ground target area,can provide high-quality imagery at the long standoff distances in the range of 10 km to 100 km when flying at 10 km to 20 km.The high-altitude long-range aerial camera has been widely used in aerial remote sensing because of its unique advantages of long-range imaging,high-resolution imaging,and high-precision geo-location.The high-precision geo-location is the key to obtain the accurate battlefield information and achieve accurate strikes.In the complex aviation environment,the target geo-location is very difficult,especially for the aerial camera which obtains the image with the high-altitude,long-range,and oblique angle.Therefore,this article presents a geo-location algorithm for the high-altitude long-range aerial camera,analyzes on the main factors that cause the geo-location error,and improves the geo-location accuracy.This article discusses the theoretical basis and development status of ground target geo-location technology for the high-altitude long-range aerial camera,and systematically studies the various aspects of target geo-location technology.In order to obtain the geographical position of the ground target accurately,a geo-location algorithm based on the digital elevation model(DEM)is developed for the high-altitude long-range aerial camera.According to the model,the influence factors on the ground target geo-location calculation accuracy are analyzed by the Monte Carlo method,which provide theoretical guidance for engineering applications.The target motion characteristics was analyzed deeply,the interactive multiple model(IMM)Kalman filtering(KF)was designed for improve the target geo-location accuracy further.A registration algorithm is proposed for aerial remote sensing image based on geographical position information to match the image which does not have obvious features.Finally,the geo-location algorithm based on DEM was migrated on DSP chip,and the geo-location module was manufactured.The validity of the geo-location algorithm and the registration algorithm is verified by a flight test.The main research content of this article can be summarized as follows:In order to obtain the geographical position of the ground target accurately,a ground target geo-location technology based on DEM is proposed for the high-altitude long-range aerial camera.According to the aircraft position and attitude information which is measured by the airborne global position system(GPS)/ inertial navigation system(INS)integrated navigation system and the gimbal angles information from the encoder,the target pointing vector in the Earth-centered Earth-fixed(ECEF)coordinate frame is solved by the homogeneous coordinate transformation.The target longitude and latitude can be solved with the elliptical earth model and the DEM.This geo-location method can be applied in the rough terrain area without a laser range finder(LRF).The main influence factors on the ground target geo-location calculation accuracy are analyzed by the Monte Carlo method.The simulation results show that the terrain error has a great effect on the geo-location accuracy,and the terrain error is the most influence factor on the geo-location accuracy when the imaging inclination angle is less than 30°.By using the geo-location algorithm based on DEM,the geo-location the geo-location error is less than 30 m when the imaging inclination angle is 0.When the imaging inclination angle is 0~70°,this geo-location algorithm based on DEM can improve the geo-location accuracy 5~7 times for the target which is located at mountain area,and improve the geo-location accuracy 3~4 times for the target which is located at hill area.In order to further reduce the geo-location error,the target was imaged and measured by using monitoring and tracking capability of the high-altitude long-range aerial camera,and the geo-location data was processed with filtering.The target motion characteristics were analyzed deeply,the motion model,which the direction of target velocity vector is changing,is established,and the IMMKF was designed by using two system state equations.The simulation experiment was done to compare the geo-location result between the traditional KF geo-location algorithm which is based on linear motion model and the IMMKF geo-location algorithm.The simulation results show that the traditional KF geo-location algorithm can improve the geo-location accuracy 2~3 times,and the IMMKF geo-location algorithm can improve the geo-location accuracy 3~4 times.These simulation results can explain that the IMMKF geo-location algorithm can adapt the target motion effectively.The registration algorithm,which is based on features information of the images,is not applicable to the aerial remote sensing images which do not have obvious features.Therefore,an automatic registration algorithm is proposed for aerial remote sensing image based on geographical position information.The matching points are selected from the overlapping area of one aerial remote sensing image,then the geographical position of matching points are solved by the geo-location algorithm,finally the pixel value of these matching points in another image are obtained through the geographical position information of the matching points.This method does not use the image features,therefore,this method is adaptable to the aerial remote sensing image which does not have obvious features.The simulation results show that the registration error is less 15 pixels for the images which are obtained by the aerial camera which has high imaging frame rate and low relative measurement error.A geo-location module based on DSP chip was designed to realize the real-time target geo-location.The validity of the geo-location algorithm and the registration algortithm are verified by the flight test in which the plane flies at a geodetic height of 15000 m.Comparing with the geo-location algorithm based on ellipsoidal earth model,the geo-location accuracy was improved 2~4 times by using the geo-location algorithm based on DEM.The traditional registration algorithm is not useful for the practical aerial remote sensing images which do not have obvious features,and the registration algorithm,which is based on geographical position information,can obtained matching points accurately.In summary,based on the existing research results,this article has proposed a geo-location technology based on DEM for wide-area reconnaissance aerial camera by studying the geo-location of the high-altitude long-range aerial camera.This geo-location method can effectively improve the ground target geo-location accuracy,which is of great significance to the development of airborne optoelectronics measurement field.