I. Introduction
The conventional sensors such as radar, vision (EOR, IR), etc. used in target tracking [1]–[3] generally observe emitted (passive sensors) or reflected (active sensors) energy from the target. The observation delay in these sensors is negligible since the speed of light (electromagnetic waves) is much larger than the speed of the target. However, one trend in sensor networks is to use standard low cost sensors as microphones and geophones on land and sonar in water. The assumption of negligible target speed compared to the speed of the media cannot always be made here. In a general scenario where the target moves swiftly, even if the sensor is stationary and collects uniformly sampled (in time) measurements of the target, the actual time instants that the target is observed are in fact nonuniform (in time) due to the propagation delays and this leads to unexpected errors in the estimation algorithms.