首先分析了系统的观测性，得出了系统可观测的两个必要条件。

System observability is examined and two necessary conditions for the system to be observable are obtained.

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可观测性分析是无源定位与跟踪系统的前提和基础，只有满足可观测条件才能对系统进行正确求解。

Observability analysis is the basic and prime task in passive localization and tracking system, for only when the system is observable, it can be determined with unique and definite solution.

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然后，通过对误差方差阵逆矩阵秩的分析，比较详尽地分析了不同数量视线观测条件下导航算法的可观度和可观性。

Then, navigation system observability and observable degree with different quantitative line-of-sight measurements are analyzed in detail by rank analysis of the error variance inverse matrix.

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