The TH-1 satellite is the first stereo mapping transmission satellite in China,and the primary mission goal of the satellite is for topographic mapping at 1∶50 000 scale and high-accuracy location without Ground Control Points (GCPs).1st,2nd satellites of TH-1 were launched on August 24,2010,May 6, 2012,and 3rd satellite was launched on October 26,2015.Now,three satellites of TH-1 are well operating on its orbit.After evaluation,the location accuracy of 1st satellite without GCPs is 10.3 m/5.7 m (horizontal accuracy/vertical elevation accuracy),and the location accuracy of 2nd is equivalent with 1st satellite.In this paper,the system overview of TH-1 and the key technical in ground image processing are introduced. Then,the preliminary location accuracy of 3rd is assessed.The results are shown using three routes images:the location accuracy of 3rd is higher than 2nd,and can realize high accuracy location without GCPs,in which the horizontal accuracy is 7.2 m,and the vertical elevation accuracy is 2.6 m.%天绘一号卫星是我国第一颗传输型立体测绘卫星,主要用于无地面控制点条件下高精度定位及1∶5万比例尺地形图测绘.01、02星分别于2010年8月24日及2012年5月6日成功发射,03星于2015年11月26日发射,目前3颗星在轨正常运行.01星定位精度经过系统检测后,定位精度为10．3 m/5．7 m(平面/高程),02星定位精度与01星精度相当.本文首先简要介绍了天绘一号卫星的总体概况及其地面处理系统中的关键技术,重点对03星的无控定位精度进行初步试验评估.通过国内外3条航线的试验发现,03星较02星精度有较大提高,在无地面控制点条件下可实现平面7．2 m、高程2．6 m的定位精度.
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