Preliminary Location Accuracy Assessments of 3rd Satellite of TH-1

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). 1^st, 2^nd satellites of TH-1 were launched on August 24, 2010, May 6, 2012, and 3^rd 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 1^st satellite without GCPs is 10.3 m/5.7 m (horizontal accuracy/vertical elevation accuracy), and the location accuracy of 2^nd is equivalent with 1^st 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 3^rd is assessed. The results are shown using three routes images:the location accuracy of 3^rd is higher than 2^nd, 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