无初始化的GPS辅助空中三角测量

GPS-supported Aerotriangulation with Ambiguity Resolution on the Fly

简要介绍了以航线为单元 ,通过相位平滑递推算法在航求解双差载波相位观测量整周相位模糊度 ,进而确定各摄站空间位置的无初始化GPS动态定位原理 ,对某测区一组实际航摄资料进行GPS数据处理和GPS辅助光束法区域网平差 ,证实所介绍的算法是正确的、有效的 ,所获取的GPS摄站坐标可满足空中三角测量的精度要求 ,并且用该数据与经初始化GPS动态定位获取的GPS摄站坐标数据进行GPS辅助光束法区域网平差的总体精度是完全一致的。

In the ordinary operation of GPS kinematic surveying on aerial triangulation,a long_time static initialization is necessary to solve a correct ambiguity before the start of the flight.Even as we know,the static initialization is a time_consuming,costly,and difficult procedure.Sometimes the flight mission has also to be interrupted and the static initialization must be executed again because the cycle slip in carrier phase measurements is created.In order to obtain continuous records of GPS signals,we stipulate some constraint norm for the aerial photographic flight of GPS blocks.In fact,this is harmful to the actual application of GPS_supported aerotriangulation.Therefore,it is important and urgent to investigate a kind of approach of camera air positions determining by differential kinematic GPS positioning with ambiguity resolution on_the_fly (OTF).This paper will describe such an approach adopted in our practice.Firstly,we use a recursive algorithm of phase smooth based on the carrier phase difference between adjacent epochs to get the smooth pseudo_range of the C/A code measurements at each epoch.Secondly,we solve a float estimation of ambiguity for the double difference carrier phase's observables at a strip using the above smooth pseudo_range.Finally,we determinate 3D coordinates of the exposure centers of the airborne camera by means of the obtained ambiguity solution.This approach is implemented strip by strip instead of whole block.It does not consider the cycle slips happening during the turn around from one flight line to the next,so that the aerial photography is able to perform in the conventional operation specification.For testing the accuracy of positioning projective centers of airborne camera by the above method and efficiency of GPS_supported bundle block adjustment,a set of actual aerial photos with GPS data taken from Tianjin project was selected and processed by software DDKIN (DGPS dual frequency kinematic surveying) and WuCAPS GPS (Wuhan GPS_supported bundle block adjustment).The achieved results have shown that our proposing scheme is feasible as well as the overall accuracy of GPS_supported bundle block adjustment is closer identical between ambiguity solutions initialized on the ground before taking off and resolved on the fly.The OTF algorithm,however,will greatly relax the operational constraint for the aerial photographic flight of GPS blocks and be of great importance to apply widely GPS_supported aerotriangulation into practical production.