Optical co-relation & scene matching technique is used ONLY by man-in-the-loop guidance systems of the type used by PGMs like Taurus KEPD-350, Delilah, Popeye, Spice, etc. Here, a two-way data-link transmits the image of the target constantly to the launch-aircraft’s pilot, which means that the missiles are NOT autonomous but are guided all through their flight profile by human intervention. Cruise missiles like Nirbhay, CJ-10, TLAM, Babur, etc on the other hand make use of active on-board RF sensors—SAR seeker—for terrain profiling & then using the scene-matching technique by comparing the profile of the scanned image with those that are stored in the cruise missile’s on-board mission computer (these images being obtained earlier by SAR sensors mounted on various recce platforms). That’s why on TLAMs there’s always an avionics LRM called DSMAC illuminator, i.e. an active RF sensor. In this arena, the Soviets were the technological pioneers. DSMAC illuminator is by no means an optronic sensor as many would like to believe or assume.
1-metre accuracy has never been attained to date by any autonomous cruise missile, but only by those man-in-the-loop tactical PGMs making use of IR sensors & two-way data-links. Even the BrahMos-1 has 3-metre accuracy thanks to its on-board SAR seeker making use of DSMAC technique. For nuclear-armed Nirbhay, even a 100-metre accuracy is excellent, given the fact that its nuclear warhead will be highly destructive.
