@gambit: from what I understood; the LO aircraft have very small RCS (like a bird) and is filtered out by the firmware as clutter. but... the clutter/birds wont be moving as fast as an airplane. so if we give the radar a firmware upgrade to show "fast moving clutter" on the radar, will the stealth of these planes be compromised?
One of the major issues with clutter is its distributive property...
RADAR CLUTTER IN AN AIR DEFENSE SYSTEM. PART 1. CLUTTER PHYSICS,
The report provides an analysis and physical interpretation of the various mechanisms giving rise to radar clutter. Both volume-distributed clutter (rain, chaff, etc.) and surface-distributed clutter (terrain, sea, etc.)
So how does this property related to a bird and its RCS?
The dynamics and radar cross section density of chaff clouds
A new chaff cloud model is described which is based on fundamental principles with modifications based on laboratory observations. Excellent approximations to the exact physical model have been developed which can rapidly predict the chaff fiber density and orientation as a function of location, time and fiber characteristics. Using this Information, the time varying RCS density is determined for any frequency and polarization anywhere within the chaff cloud. The results are consistent with full scale observations, and the computational speed allows the model to be integrated into existing real time radar simulations.
Note the highlighted.
I pointed out before here that radar detect birds by more by their beaks than by their bodies, of which the latter with its curves and feathers are natural absorbers. The problem here is that in order to detect birds, insects and rain, the RCS for these items are so low that to detect them from afar, we cannot rely on individual RCS but upon the cumulative effects of large volumes of bird beaks and the result is a sort of cloud on a radar scope and whose behavior is that of a flock of bird that we determine to be birds.
How NEXRAD sees the atmosphere
Birds typically fly at least 10-15 knots faster than wind speeds, and not necessarily downwind. On the other hand, insects, precipitation, and other aerial entities, are wind-blown. They generally move at the same speed and in the same direction as the wind. Targets moving at least 10 knots faster than the prevailing wind, or moving in crosswind or headwind conditions, are almost always birds.
In order to distinguish on a radar scope an individual bird, and it is possible to do so, the bird would have to be practically within visual horizon. That does not mean we can see the sparrow at the horizon. Our eyes are not that refined. It just mean that the sparrow is not beyond the visual horizon. Our eyes cannot make out the sparrow but the radar can. However, at this close range, the hostile aircraft has already dropped its bombs.
RCS density calculation is necessary if we are to detect birds (plural) and track their migration patterns. Same for insect swarms. Same for rain via clouds. Birds, insects and rain mass are called 'volume clutter'. RCS density is RCS per unit volume, meaning the overall mass is broken down into smaller parts and these parts will have their RCS calculated. If a single bird is separated from the flying mass, it will be quickly lost from radar, despite the system's lowered clutter rejection threshold. Remember...The system is looking for bird-like RCS but is also looking at around triple km distance.
Airborne clutter, especially with birds and insects, are not constant. From one moment, some birds will separate themselves from the mass. The next moment they may rejoin and perhaps even new birds will add their individual RCS to the mass, effectively increasing the mass overall density, making on-the-fly RCS density calculation by the radar resource intensive.
An F-22, or several F-22s for that matter, at several hundreds km from target, will have its bird-like RCS part of this distributive clutter and will be nearly impossible to distinguish from the real birds despite having the greater Doppler component. Doppler separation works best when there is a clear RCS difference between objects. But when this attacker is close to the target, then indeed the target will detect and track this 'bird'. Of course, it will be too late.
Surface clutter is also a great hiding place for current generation of US radar low observable aircrafts. We know very well how a city will look on a scope and essentially every city in the world has a unique RCS base upon the city's architecture.
Giza - Radar Picture of Giza
The side-looking radar illuminates the scene from the top, the two sides of the pyramids facing the radar reflect most of the energy back to the antenna and appear radar bright; the two sides away from the radar reflect less energy back and appear dark Two additional pyramids can be seen left of center in the lower portion of the image. The modern development in the desert on the left side of the image is the Sixth of October City, an area of factories and residences started by Anwar Sadat to relieve urban crowding.
Note the highlighted, it is very important.
Corner reflectors from man-made objects will appear 'radar bright', the Giza Pyramids just happened to be so electronically prominent because of their physical size. Same for the Eiffel Tower in Paris. But what make the Eiffel Tower even more unique than the Giza Pyramids is its metal lattice structure. To the average military radar, the Eiffel Tower is practically a trumpet blown by the great Miles Davis. Any city whose urban areas have chain link fences will have extraordinary scintillating bright spots on the ground due to fences' lattice structures. A flight of F-35s, even with their high Doppler components, will have their bird-like RCS masked by these 'radar bright' flashes.
This is why these aircrafts are so dangerous.
