Precise baseline determination for the four-satellite InSAR constellation HT-01 with ambiguity resolution constraints

Distributed interferometric SAR (InSAR) systems is evolving from dual-satellite configurations to multi-satellite systems. The Hongtu-01 constellation (HT-01), world’s first four-satellite interferometric SAR system utilizing a cartwheel formation, marks a significant milestone in China. Precision orbit determination (POD) and precision baseline determination (PBD) are essential for the successful execution of the HT-01 mission. However, baseline determination poses a challenge to differential GPS techniques due to the requirement for simultaneous determination of multiple baselines efficiently. As an alternative, absolute orbit can be computed individually for each spacecraft and used for the generation of precise baseline products. In addition, single-receiver ambiguity resolution (SR-AR) and double-differential ambiguity resolution (DD-AR) could be employed as constraint to enhance the accuracy of POD. In this paper, the performance of orbit and baseline determination for HT-01 is comprehensively evaluated. For further improving POD precision, receiver GPS signal phase center variations (PCV) models with 3 × 3°grid map and maneuver handling was employed. Among POD solutions, the results for the SLR residuals are 2.12 cm, 1.94 cm, 1.59 cm and 1.53 cm corresponding to the ambiguity-float, ambiguity-float + PCV, ambiguity-fixed and ambiguity-fixed + PCV orbit solution, respectively. Furthermore, we analyze the baseline difference between the baseline solution of SR-AR with approximately 92 % ambiguity fixing rates and baseline solution of DD-AR with almost 100 % ambiguity fixing rates. Result exhibit baseline consistency of approximately 1∼2 mm on each direction. Besides, baseline overlapping with 3D RMS consistency shows 1.07 mm and 1.23 mm for DD-AR and SR-AR, respectively. The above solutions can be considered as an effective approach for prospective formation-flying remote sensing missions with multi-baseline determination for a multi-satellite constellation.