Position and orientation system (POS) is an important part of airborne remote sensing system, it is used to measure and compensate the motion errors of airborne sensors in course of imaging. In-flight alignment is an effective way to improve the accuracy and robustness of POS in its operating cycles. In the traditional in-flight alignment methods, large initial alignment errors result in the fact that nonlinear error models and nonlinear filters must be used, which means much calculation load will accompany the system. To avoid the large initial alignment errors, in this paper, a new in-flight alignment method with fewer calculation loads is proposed. The error propagate characteristic of POS is analyzed first, and state transition matrix is used to record the initial alignment errors propagate process in every calculation step. After observability analysis of the new method, the in-flight alignment is carried out according to the navigation errors and the error state-transition matrix of POS. To validate the proposed in-flight alignment method, car-mounted experiment and flight test are carried out. Experiment results show that, the proposed in-flight alignment method can improve the accuracy and the robustness of POS with fewer calculation loads.
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