...awacs they also know that what indian fighter jets weapon carries...
How is this supposed to work? Would you be kind enough to elaborate? I agree that it can detect the type of aircraft but weapons on board!?!?
you can detect (approximates) the type of aircraft, speed, direction, etc using a radar. Once that has been determined, it is possible to filter out standard information and estimate the amount and type of weapons being carried by the plane.
Weapons themselves are big time reflectors, and that is why Stealth fighters carry them on internal bays.
I am not exactly sure how much this tech is applied and with what success, but in theory it is possible. At the very least, you can detect what kind of mission it is carrying out.
Inverse Synthetic Aperture Radar (ISAR) is a technique to generate a two-dimensional high resolution image of a target.
In situations where other radars display only a single unidentifiable bright moving pixel, the ISAR image is often adequate to discriminate between various missiles, military aircraft, and civilian aircraft.
Inverse synthetic aperture radar - Wikipedia, the free encyclopedia
Remember the picture of the Indian MKI Kayani allegedly showed the Americans..
What I am trying to say is that the missile is not flying on its own. It will be attached to the aircraft pylon. Since most of the system will be hidden multiple reflective surfaces and since there will be no relative motion of the missile (wrt the aircraft), it is hard to detect the missile alone using ISAR unless it is launched.
The (more expensive) solution is in inverse SAR (iSAR) if the desire is to have a more precise target resolution regarding target structure, not merely target speed, altitude or heading. So here we go...
I have posted the above illustration here before and it is important that interested readers understand that is how a radar sees an aircraft. Each dot represent a 'scattering' feature on the body, aka 'scattering point'. It could be anything, from an air vent, to a small UHF comm antenna, to the large vertical stab. Each of the example could have its own scattering points on its own surface. The air vent could have multiple holes or slits and each of them is a scattering point whose combined echo power equal to 'air vent'. So if we go up one level, each elongated oval represent the echo power strength of a distinct scattering point that may or may not be a composit of many smaller scattering points. The largest and most powerful echo would be a wing. For clarity we will not mind the aircraft's fuselage for now.
When the wing is in a 'clean' configuration (a) it will present the lowest echo power strength it can possibly give. When the wing is in (b) or (c) for take-off and landing, then we can see that there are additional mechanical contraptions produced by the wing: flaps and slats. They inevitably will increase the wing's overall echo power.
As usual I will provide at least one source lest some people think I making this sh!t up...
Radar imaging and multiple scatter-point localization
The fundamental task of range-Doppler imaging is to reconstruct the spatial function of reflectivity of a target from the returned radar signals. Radar imaging is investigated from the point of view of multiple scatter-point localization. Both motion compensation and image formation are solved simultaneously as a maximum likelihood estimation problem. Generally, the computational load is extremely heavy mainly because a multidimensional search is required. By introducing DFT and utilizing FFT, this may significantly reduce the computational complexity at a sacrifice of imaging quality. A further simplified imaging algorithm is derived for a case of the orbital motion model of the target being a quadratic equation. Computer simulation results are also included.
Scatter points localization mean the question: Are these scatter points in a cluster? So if they are and the cluster persists over time, then we have a valid target, be it a storm cloud or a B-52 bomber.
Now if we add on the wings pylons that carries external fuel tanks and assorted weaponry, all of these items are themselves scattering points that themselves are composits of many smaller scattering points. The next logical step in radar detection
WAS to ask: Is it possible to separate out those many smaller scattering points to increase target
STRUCTURAL resolutions? There are target characteristics and behavior resolutions, such as speed, altitude and aspect disposition (angle) to the seeking radar. But target
STRUCTURAL resolution deeper than what we can obviously dissect: wings, vertical stabs, horizontal stabs, cockpit, etc...Required additional transmission frequencies, pulse characteristics manipulations and related hardware issues that increase system complexities and naturally cost.
The reader must remember that scattering points comes from
PHYSICAL STRUCTURES.
Radar Bands
X band radars operate on a wavelength of 2.5-4 cm and a frequency of 8-12 GHz. Because of the smaller wavelength, the X band radar is more sensitive and can detect smaller particles. These radars are used for studies on cloud development because they can detect the tiny water particles and also used to detect light precipitation such as snow.
The highlighted is the clue. Smaller particles are smaller physical structures, are they not? Meters length freqs can only give us target characteristics and behaviors. It is the centimetric and millimetric bands that upon impact then echo off the body that contain the physical details that we want, in other words, the information have been there
ALL THIS TIME, in other words, the echo is already telling us that there is a missile (or bomb) on the pylon, we just lack the technological capability to distinguish missile and pylon from each other.
Enter Synthetic Aperature Radar (SAR) and its cousin inverse SAR (iSAR).
In many men's fantasy, the man is a professional photog for Playboy magazine. Say my camera has a physical aperture of one meter and my stride is also one meter. If I take a shot of the model from one position, take one sidestep (one meter) then take a second shot I have just created a virtual or 'synthetic' camera aperture of two meters while the camera's physical aperture is still one meter. If I combine the two shots together, I now have a more detailed version of the model from two different angles. If I am not satisfied, and of course not, I would circle the model at one meter interval, take a shot at each pause point, and continue until I have completed a circle. This is SAR.
What if the model move instead of the camera? If the model turn 90deg and the camera take a shot, now I have a virtual or 'synthetic' aperature of two meters. At the end, after three 90deg turns, I would have a virtual or 'synthetic' aperature of four meters. This is inverse SAR (iSAR). This is completely different from when the camera was the one in motion. Because the model made only four turns I could have a lower resolution of her than when the camera was in motion. This is not good as we want to know as much of her many 'scattering points' as possible. The more we know of her the more issues sold, right? So if the model make only one degree turn per camera shot, at the end, I would have a virtual or 'synthetic' aperature of 360 deg. With iSAR, camera (or radar) aperature is target dependent.
The most important thing to remember in both SAR and iSAR is that there
MUST be motion by at least one side. If the seeking radar is in motion, then it is SAR. If the target is in motion, then it is iSAR.
Now what if both the model and the camera are moving at the same time? Not only is she rotating her body (wow) but also moving towards and away from the camera? This is no different than the AWACS and target relationship
IF there are SAR and iSAR processing involved. The data processing is not only doubled but tripled because both sides are moving. When the aircraft discharge a missile or bomb from itself, it loses a major scattering point and its overall RCS decrease. At the same time there is a distinct cluster of scattering points moving rapidly away from the aircraft. Any response at this time is the proverbial 'after the fact' action and may be too late.
The more we know about the target, not only of its characteristics and behaviors, but what it looks like
BEFORE it make some kind of decision, the better we can formulate a response and perhaps even take preemptive actions in our favor.
We are not yet at the point where we can dissect so much information from an echo that we can see a BVR target with equal clarity as if the target is literally in front of us. Currently at best, the SAR images are like early BW television. So what we do is create algorithms, based upon hardware capability, that if we detect so-and-so spikes inside a larger spike with such-and-such pulse echo characteristics then 'kinda-sorta' guess that it is a fighter or bomber.
For example:
In the bow view of the above ship image, we can see there are many scattering points, from the mast top to the anchor and anywhere in between. Ships on water are not static. As a ship in a side-side rolling motion, those many scattering points create localized and
PREDICTABLE Doppler shifts. So we create an algorithm within our iSAR processing to say that if we have a highly localized and predictable Doppler shift cluster -- classify the target as a ship. Better yet...Ships of different sizes will have different roll rates. A destroyer is the lightest so it will have the highest roll rate. Carriers and tankers can have as much as 30 seconds in calm sea.
So when a fleet is in motion in rough sea, destroyers can have double digits roll degrees from their equilibrium while the aircraft carrier flagship will barely break five degrees from its equilibrium. An airborne iSAR processor will see many localized and predictable Doppler shifts against what it knows to be water background, it will analyze each cluster and see distinctions between the many clusters, it will see the clusters with the highest roll rates are in a circle around the cluster with the lowest roll rate,
voila: a fleet with at least one capital ship and assorted escorts. We do not need to see this fleet in details. From Doppler shifts alone, iSAR processing already alerted us to a naval threat and based upon that large cluster with the lowest roll rate, we can customize our defenses to meet an aircraft carrier, or at least we suspect it to be an aircraft carrier.
Not all airborne radars have SAR capability...
Wedgetail - Australia's Pocket AWACS
Australia's "Pocket AWACS"
The only capability missing is the JSTARS style high resolution SAR surface mapping and GMTI surface target tracking, both of which are secondary capabilities in the regional geographical environment, dominated by littoral scenarios (and both of which may be growth options given declining long term costs in computer hardware).
It is pointed out that a missile is fixed to the pylon and exhibit no motion relative to the pylon, the wing and eventually the aircraft itself, therefore iSAR processing on this scattering point is not possible. This is incorrect. True...That the missile is fixed but we are living in a 3D environment. Go back to the Playboy model and camera example for a moment. If the model raise an arm in front of her very attractive front side, if either the camera or the model move, her arm will clearly exhibit different motion than her body. Take a soda can, open the tab and leave it raised. Now move the can any direction. The raised tab will 'move' of sort. With iSAR processing, what matter is the scattering point's movement that is relative to the seeker radar, not in contrast to the main body that carries said scattering point.
International Ice Patrol
The ISAR is a synthetic aperture radar mode that takes advantage of target motion relative to the antenna.
http://stl.uml.edu/PubLib/Giles, Acq xband move.pdf
...generating doppler shifted and standard ISAR imagery of either/both the moving and stationary vehicle.
Tabulated is the center frequency phase shift one might observe for a moving vehicle using this radar. Since in-scene objects have different relative velocities, i.e. the top and bottom of the tank tracks in reference to the tank frame, each will appear to separate in the doppler shifted images and HRR profiles.
The top track exhibit a different Doppler shift than the bottom track. This is on the same vehicle. Another example from the same source...
At a Doppler velocity bin capturing the scattered signal from the targets chassis and hull, observed in the center ISAR image is scattering beyond the vehicles range extent generated from a pair of louvered compartments in the back of the BTR-70. Scattered signal was observed from the top of the BTR-70s four hubs, and tires, at Doppler velocities of 1.4, and 2, times the chassis velocity, respectively.
As shown, a body's surface features will generate their own Doppler shifts, from louvered windows to wheel hubs. Wheel hubs move, but not windows, but because the tank's surface protrusions are 3D features on the body, when the body itself is motion with many redirections, those surface features will generate their own Doppler shifts.
For the aircraft, the missile's radar echo may be masked by the aircraft's echo, but it is there nevertheless. When the aircraft maneuver, the missile will present its own Doppler shift to the seeker iSAR.
Creating an effective an airborne SAR/iSAR processing platform is not a casual endeavor in development and in purchase. Against other airborne targets such as small and agile fighters, SAR/iSAR processing can be impossible under certain conditions such as if the target is in terrain following and terrain avoidance flight mode. Basic SAR operation require the seeker to be looking at an area from a side perspective. If the target is behind a ground feature, a hill or even a building, and if the seek angle is low enough, the target is invisible to the SAR seeker.
In summation...It is already feasible to distinguish a fighter and bomber thru SAR/iSAR processing...But it is expensive and the system require high levels of training in usage and maintenance.
Finally...Do not mix up inverse-SAR (iSAR) and interferometric-SAR (InSAR). The latter type, InSAR, involve satellite imaging...
What is InSAR?
InSAR stands for Interferometric Synthetic Aperture Radar. This is thus a remote sensing technique that uses radar satellite images.
...And that is another can of worms.
Gambit i would have never understood it until the "playboy" example!!! but thank you!!! for a great post!!! very detailed & very well explained!!!!! 
