In the strapdown inertial navigation system (SINS) calibration, the observability of SINS error states has significant impacts on calibration results. In order to analyze the observability of SINS error states quantitatively, this paper proposes the observability degree for the states of linear time-varying systems. It is shown that the proposed observability degree illustrates the sensitivity of state estimations to disturbances and determines the upper bound of estimation accuracy. Based on the proposed observability degree, the sufficient and necessary conditions for the states to be observable are presented. In addition, an experiment of ship-mounted SINS calibration is given to validate the proposed observability degree. According to the experiment results, the proposed observability degree can make accurate evaluations on the observability of SINS error states, thus providing direct understandings on the accuracy of calibration results.

在捷联惯性导航系统（SINS）校准中，SINS错误状态的可观察性会对校准结果产生重大影响。为了定量分析SINS误差状态的可观测性，提出了线性时变系统状态的可观测度。结果表明，所提出的可观察度说明了状态估计对干扰的敏感性，并确定了估计精度的上限。基于拟议的可观测度，给出了可观测状态的充分必要条件。此外，还进行了舰载SINS校准实验，以验证所提出的可观察性程度。根据实验结果，