Observability conditions for fusion of asynchronous measurements from multiple passive sensors

Target tracking with multiple synchronous passive sensors is well studied in the literature. If the LOS measurements are not synchronized, the formation of composite measurements (full position) requires at least three LOS. In this paper, we examine the case where the sensors initiate tracking with a random constant offset. Furthermore, to validate the numerical results on the required number of LOS for both synchronous and asynchronous measurements, an analytical proof is provided.