As a note to subject, The advanced sensors and missiles using these sensors offers great capabilities If you know their minus and plus. There is nothing unbeatable in battlefield. The best thing to do is to use the best sensor in perfect time and environment in accordance to changing field conditions.
IIR missiles are sneaky, dangerous systems cause of having passive image sensors. The enemy may not even realize the missile approaching to him If the platform itself doesn’t have a MWR to warn the pilots but IIR missiles come with some limitations which put them lack behind of RF missiles in some aspects. For example, The optic of IIR seekers are geting hotter in higher speeds by friction force of air so the image to be taken by sensors meet with clutter effects which may cause a serious problem for the detection of targets. The Hisar-O will overcome the heating problem with a composite canopy covering the lense. It will be ejected in terminal phase so the air will interact the vision of seeker in relatively less time scale.
Contrary to Rf seekers, IIR sensors can not measure the distance of target so they can not calculate the perfect timing for detonation of warhead so IIR missiles require laser fuse sources equipped the sides of missile body which is activated in terminal phase. If the missile miss the target, The laser source to be reflected by target fuselage will be absorbed by same laser fuses and It will be the order of detonation for warhead. The principle seems perfect but It costs extra money.
Contrary to radar seeker modules, The sight angle of IR sensors have narrower than RF modules. Older generation IR missiles just travk the heat of target so They are good at chasing the route that target navigates and so, They sacrifice most of kynetic energies while following a longer range.
To solve this disadvantages, Newer IIR missiles are smarter and use the gimbaled seeker head combined with "proportional guidance" in order to avoid oscillation and to fly an efficient intercept path. Gimbal seeker turns towards target to lock on, while Missile is proceeding a steady course different than the direction of seeker. A gyroscope inside of seeker continuously calculate the relative bearing (constant bearing) thanks to data taken by gimballed seeker, while the distance between them are decreasing. If the constant bearing chances a bit thanks to escape maneuvering of target, Gimballed seeker will follow the move, while the processor in missile will immediately draw a new route to make bearing angle the constant again until missile and target collide.
4axis gimballed seeker of Hisar-A/O IIR seeker!
Contrary to RF seekers, Weather condition is an important factor which decrease the performance of IIR seekers. Clear skies on regions having relatively high average temperature climate is the place where IIR seeker perform the best but Rainy, Foggy, Misty weather conditions robustly effect the detecting range/sight performance of seeker at terminal phase.
Detection range (km) of different IIR sensors compared to naked eye.
Category I: visual range 1220 meters
Category II: visual range 610 meters
Category IIIa: visual range 305 meters
Category IIIc: visual range 92 meters
The naked eye performs better than any IIR sensor in category-III heavy foggy condition, because heavy fog clouds can't be penetrated by thermal radiations. In Category-II, LWIR is 4x superior to MWIR. In category-I, It is again LWIR sensor performing the best. Rain can significantly reduce target contrast on IIR sights and LWIR or MWIR perform similarly in the presence of rain. Range of senaors on rainy weather is a dramatic drop off in the 100-500 meter range.
so the best solution to oversome the difficulties the mother nature create is the dual-band IIR sensor technology but RF missiles are a must as well.
@Philip the Arab