Active vs. passive tracking: When to illuminate?

This paper seeks to address whether active or passive tracking is preferable in terms of centroid-Track error. Active tracking has the advantage of allowing for SWaP-limited source control to scale SNR. With coherent illumination, however, speckle noise gives rise to a fundamental limit in tracking precision. On the other hand, passive tracking relies on incoherent illumination with speckle-free return. The drawback in this case is that SNR itself is inherently limited, thus limiting precision with respect to tracking measurements. In our analysis, we first present the theory that drives limiting factors of both active and passive tracking schemes. From these limitations we then estimate Strehl ratio at various SNRs for direct comparison of active and passive performance. We consider objects of various shapes and sizes, study both well-resolved and unresolved objects, and anchor our findings to first-order simulation results that demonstrate significance in the design of tracking systems.