Synthetic aperture radar for the IAF

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Shankar
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Synthetic aperture radar for the IAF

Post by Shankar »

The need for synthetic aperture radar in IAF is increasing by the day.For any effective ground or maritime strike acurate target designation and subsequent missile guidance to target is not possible without a high quality SAR .The standard military use radar is too big and too power hungry and also difficult to restrict to single use and as such most of them are capable of switching from low resolution broad beam search to high resolution narrow beam attack mode .However because of its ver nature synthetic aperture radars can easily improve the versality of a standard system one of which is medium resolution strip mapping for uninterupted ground survilance images .Another is very high resolution spot light mode used to idetify ground targets and ships at sea.

However it is in this spot light mode things get a bit difficult forSAR.Since the synthetic aperture depends on a moving platform moving targets cause problem.Dppler effect distorts radar signas just like it does sound waves.By adjusting the dopplershift of the moving objects a clear image can be produced of the spot lit object which otherwise would be a smear.

An image clear enough t identify a spot lit ship is another matter.Radar platform,ses and ship are all moving independently creating a processing nightmare.The answer came from an inverse sysnthetic aperture radar which used the doppler shift of the moving vessel to create an image instead of filtering it out.The ships movement creates the synthetic aperture which simplifies the processing alogorithm.
Himanshu
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Re: Synthetic aperture radar for the IAF

Post by Himanshu »

Check this..
http://www.vectorsite.net/twbombb.html#m7

What we need..
http://www.vectorsite.net/avbtsv.html

BIG question is.. WHEN are we gonna have these??
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Re: Synthetic aperture radar for the IAF

Post by JaiS »

I remember Nitin mentioning that ISRO had created a SLAR ( Side Looking Airborne Radar), which had been offered to the IAF, but was turned down. SAR's, in most cases, have to be SLAR's, in order to synthesize the virtual antenna. Hope this thread will be utilized to gather information about potential SAR systems for the IAF.
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Re: Synthetic aperture radar for the IAF

Post by JCage »

Yeah. The powers that be shot it down. Too boring, too desi. For those who want references it was first reported in the Indian Defence Review, two years back. Reported by a p1ssed off IAF gent involved with the successful trials.

Incidentally the MKI has a SAR mode. The LCA has also got a range of A-G modes. The Kopyo on the Bison ditto.

The UAV's we are getting from israel- the Searchers and Herons...the Israelis market SAR with those systems as standard.
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Re: Synthetic aperture radar for the IAF

Post by Sunil »

Hi,

As nitin says IDR had an article about this. I think it said something like this:

"A ISRO (corrected thanks to Nitin) unit had produced a SAR with reasonable performance for a first attempt/proof of principle in the early 1990s. The performance was not upto `world standards' as the this was just a prototype. There were also several unanswered questions about performance parameters. However the prototype was able to perform admirably in initial tests, in atleast one test, it was able to discern the movement of a tank column in the Thar desert.

The IAF had expressed considerable interest in the project however the after the Cabinet Secretariat evinced an even deeper interest in the project, it was allowed to take the lead in the project. The project was later terminated due to a lack of adequate funds and due to the presence of cheaper commercial alternatives."

To put it mildly the project was an uncut diamond, it would take atleast 10 years for that first attempt to become a viable entity and back in the 1990s we didn't have that kind of money at all. I mean we are looking at money on the order of the LCA project, that sort of funding doesn't come easily.

One of the biggest problems in any kind of Radar application is compensating for doppler effects, this often requires a fair bit of computing power so that can also be a technology barrier.
George J

Re: Synthetic aperture radar for the IAF

Post by George J »

Cabinet Secretariat read RAW wanted to develop it and didnt have the money for it?? Interesting.

Why do you think that a SAR development is on the same scale of the LCA in terms of monies required, scientific rigour and finally importance?
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Re: Synthetic aperture radar for the IAF

Post by Vick »

What kind of radar will the RISAT have?
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Re: Synthetic aperture radar for the IAF

Post by Rudra »

the time has arrived to move beyond the tactical
tools like SAR modes on fighter radars, UAVs etc. These can help the pilot or batallion commander to bag a few tanks , discern movement of a column etc.

What we need is a strategic Corps or ARC-RAW level
assets , phalcon sized and mounted on a 737/IL76/A321 chassis...capable of JSTARs-ish battle control..patched into all army/AF networks.

range, transmit power, granularity, number of T/R modules, processing power would be 100 times greater than MKI.

desi-Astor! desi-Astor! -> the next phase of IAs RMA.

all PLA/PA movements in their so-called communication zone 100-300km behind the active frontline would be known well in advance.
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Re: Synthetic aperture radar for the IAF

Post by JCage »

Sunil,

Thats a beauty of a report. Do you have the source if possible?

The report I was referring to referred to having used an already developed ISRO item and used it on an An 32 platform.

Agree on funding required, but SAR devpt - say not world class but 3/4 there itself should have been deemed acceptable. Should not have been a problem . SAR on UAV's, transport aircraft etc would typically be a much easier proposition than a system designed for fast jets.
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Re: Synthetic aperture radar for the IAF

Post by Sunil »

Hi GJ,

I am guessing that irrespective of who takes the lead in the project, the work would have to be done by the same people, and given the ambient level of technology, the costs for developing a working SAR system that would meet the needs of the end users would be similar to the cost of developing the LCA. One is looking at thousands of crores with atleast 50% in FE. Back in 1990s FE was in short supply.

I think you are correct when you suggest that the LCA project had much greater depth, but at the time that the SAR project was conceptualized, none of the LCA tech was available off the shelf (as it is now) so that may have added to development costs. For example the data processing computers needed to work the SAR weren't ready in those days (unlike now).

Also as Rudra points out, the Secretariat probably had different ideas on end-use than say the IAF or the IA. For example the needs of battlefield surveillance are very different from say strategic forecasting, even a slightly lower resolution SAR can be used for identifying strategic patterns (eg. increased movement along a highway or rising traffic on a water body etc...) but if you want to do battlefield surveillance, that is a far more demanding and expensive task. This may have a factor in deciding who takes the lead on the SAR projects.

As regards the Secretariat not having money, boss everyone in the 1990s felt the pinch. Government spending for extraordinary things contracted as the nation reeled under security crises. Also it is not like SAR was the horse in the Secretariat's stable, they probably had many mouths to feed. Given a choice between a long and expensive development process for SAR against say less pathbreaking but cheaper competitors, it is highly possible that the Secretariat made the only choice it could.

The IA/IAF/IN adopted the more economical approach towards the entire matter and settled on locally developed UAVs with gyro stablized cameras and telemetry.

Hi Nitin,

It is the same report. It is an ISRO team not a DRDO one, I got that wrong.
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Re: Synthetic aperture radar for the IAF

Post by Harry »

The Elta EL/M-2032 on the Jaguar-IMs has a SAR mode. So does the N011M Bars. The Kopyo-M on the Bison has more than adequate processing power for it but SAR modes have'nt been officially mentioned.

Synthetic Aperture Radars have more to do with all weather, real time IMINT, not targetting. They have no relevance to passive homers such as ARMs, IR or TV guidance.

The MiG-25R does sport a SLAR in the nose which could reportedly record surface detail upto a range of 200 km. Without the knowledge of the exact version the IAF uses, it's to possible to tell if the SLAR is the 'Sablya/Sabre' (MiG-25RBS) or 'Shompol/Ramrod' (MiG-25RBsH). The latter provided 2-3 times better pic resolution, MTS and combined mapping/MTS mode. Also, the Sabre was limited to heights not below 55,774 feet.
George J

Re: Synthetic aperture radar for the IAF

Post by George J »

Someone once told me that the Cabinet sec and IAF do use a lot of DRDO products that you never hear about.

If the cabinet secretariate could not muster funds to bring the project to fruition then I guess funds were indeed in short supply. I think we can comfortably assume that if Cab Sec wants something it will be done. So either the system was not worth the money for them to develop or in the early 90's there really was no money for SAR and they had to devote their resources to other proximate sources of information.
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Re: Synthetic aperture radar for the IAF

Post by vishal »

I tried reading this thread when it was started and then gave it up as I didn't know what a SAR was (apart from some kind of radar). So today I Googled for the same and came up with what it is, what it does & how it works. Should help those of us who have a vague idea about SARs being important but have no cloue about the whole thing. Also, it might get more folks involved in the discussion if they knew what was being discussed.

Posting in full.
Source: http://www.sandia.gov/RADAR/whatis.html

What is Synthetic Aperture Radar?

Environmental monitoring, earth-resource mapping, and military systems require broad-area imaging at high resolutions. Many times the imagery must be acquired in inclement weather or during night as well as day. Synthetic Aperture Radar (SAR) provides such a capability. SAR systems take advantage of the long-range propagation characteristics of radar signals and the complex information processing capability of modern digital electronics to provide high resolution imagery. Synthetic aperture radar complements photographic and other optical imaging capabilities because of the minimum constraints on time-of-day and atmospheric conditions and because of the unique responses of terrain and cultural targets to radar frequencies.

Synthetic aperture radar technology has provided terrain structural information to geologists for mineral exploration, oil spill boundaries on water to environmentalists, sea state and ice hazard maps to navigators, and reconnaissance and targeting information to military operations. There are many other applications or potential applications. Some of these, particularly civilian, have not yet been adequately explored because lower cost electronics are just beginning to make SAR technology economical for smaller scale uses.

Sandia has a long history in the development of the components and technologies applicable to Synthetic Aperture Radar -- 40 years in radar, antenna, and miniature electronics development; 30 years in microelectronics; and 25 years in precision navigation, guidance, and digital-signal processing. Over the last decade, we have applied these technologies to imaging radars to meet the needs of advanced weapon systems; verification and nonproliferation programs; and environmental applications. Sandia's expertise in electromagnetics, microwave electronics, high-speed signal processing, and high performance computing and navigation, guidance and control have established us as world leaders in real-time imaging, miniaturization, processing algorithms, and innovative applications for SAR.

How does Synthetic Aperture Radar work?

A detailed description of the theory of operation of SAR is complex and beyond the scope of this document. Instead, this page is intended to give the reader an intuitive feel for how synthetic aperture radar works.

Consider an airborne SAR imaging perpendicular to the aircraft velocity as shown in the figure below. Typically, SARs produce a two-dimensional (2-D) image. One dimension in the image is called range (or cross track) and is a measure of the "line-of-sight" distance from the radar to the target. Range measurement and resolution are achieved in synthetic aperture radar in the same manner as most other radars: Range is determined by precisely measuring the time from transmission of a pulse to receiving the echo from a target and, in the simplest SAR, range resolution is determined by the transmitted pulse width, i.e. narrow pulses yield fine range resolution.

The other dimension is called azimuth (or along track) and is perpendicular to range. It is the ability of SAR to produce relatively fine azimuth resolution that differentiates it from other radars. To obtain fine azimuth resolution, a physically large antenna is needed to focus the transmitted and received energy into a sharp beam. The sharpness of the beam defines the azimuth resolution. Similarly, optical systems, such as telescopes, require large apertures (mirrors or lenses which are analogous to the radar antenna) to obtain fine imaging resolution. Since SARs are much lower in frequency than optical systems, even moderate SAR resolutions require an antenna physically larger than can be practically carried by an airborne platform: antenna lengths several hundred meters long are often required. However, an airborne radar could collect data while flying this distance and then process the data as if it came from a physically long antenna. The distance the aircraft flies in synthesizing the antenna is known as the synthetic aperture. A narrow synthetic beamwidth results from the relatively long synthetic aperture, which yields finer resolution than is possible from a smaller physical antenna.

Achieving fine azimuth resolution may also be described from a doppler processing viewpoint. A target's position along the flight path determines the doppler frequency of its echoes: Targets ahead of the aircraft produce a positive doppler offset; targets behind the aircraft produce a negative offset. As the aircraft flies a distance (the synthetic aperture), echoes are resolved into a number of doppler frequencies. The target's doppler frequency determines its azimuth position.

While this section attempts to provide an intuitive understanding, SARs are not as simple as described above. Transmitting short pulses to provide range resolution is generally not practical. Typically, longer pulses with wide-bandwidth modulation are transmitted which complicates the range processing but decreases the peak power requirements on the transmitter. For even moderate azimuth resolutions, a target's range to each location on the synthetic aperture changes along the synthetic aperture. The energy reflected from the target must be "mathematically focused" to compensate for the range dependence across the aperture prior to image formation. Additionally, for fine-resolution systems, the range and azimuth processing is coupled (dependent on each other) which also greatly increases the computational processing.

The article posted above also has an illustration which I am unable to post here. Check it out if it helps.

Some more stuff from the same website:
Synthetic Aperture Radar Movie Gallery
JaiS
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Re: Synthetic aperture radar for the IAF

Post by JaiS »

In other words, the radar, instead of transmitting and receiving in the frontal hemisphere, emits in a direction perpendicular to the motion of the aircraft ( this is not a necessity though ) and collects signals over a long period of time. These signals are then weighted over the same period of time and processed to "synthesize" an antenna.

L5
L4
L3 ------------------ (X)
L2
L1

For example, in the above case, the aircraft is moving at a constant speed in the direction L1->L5 and the target to be monitored is (X). The distance between L1-L2 is "d" and is the same for all L's(Locations). The radar starts radiates at each L, collects the returning signal and does nothing with it, simply stores it. At the end of the run, that is, at L5, all the received signals are weighted according to the time of reception of the signal, and are processed as if there was a big antenna of diameter/aperture L1-L5 and as if it had radiated at a single instant. In this manner, the effect of having a very big antenna is created ( in this case the diameter/aperture of the antenna will be d+d+d+d = 4d), or in other words an antenna has been "synthesized". Hence the name. The main advantage of SAR's is their high resolution provided by it. It should also be noted that deviations from a linear flight path complicate the processing because now the processor has to compensate for the "kink" in the synthetic antenna.
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Re: Synthetic aperture radar for the IAF

Post by Sunil »

Hi GJ,

Boss I don't know the details, but money was in short supply in the 90s, a lot of things were put on the back burner, this was one them according to the IDR article.
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Re: Synthetic aperture radar for the IAF

Post by vishal »

Originally posted by Jai SR:
The radar starts radiates at each L, collects the returning signal and does nothing with it, simply stores it. At the end of the run, that is, at L5, all the received signals are weighted according to the time of reception of the signal, and are processed ...
So it would seem that SARs have 2 major components, the emitter itself & the processing unit. If fitting both these components into a single aircraft is a challenge because of space constraints, heat, cooling requirements & power consumption would it be feasible to house these capabilities in 2 different aircraft flying in conjunction? One would do the emitting while the other would recieve, process & distribute the information. In theory, this would mean that smaller aircrafts could be used, reduced system integration problems (or would this compound the problems) & redundancy. So if an aircraft is lost one doesn't lose the entire set-up.
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Re: Synthetic aperture radar for the IAF

Post by JaiS »

What you suggest is a theoretical possibility, but the existence of detachable pod systems, like the ELTA EL/M-2060 P, EL/M-2055, EL/M-2057, suggests that the power/heat/cooling issues are not significant to the extent of a tactical fighter being unable to carry SAR system. Also, it seems to be logistically difficult to dedicate two airframes for the purpose of recce ops. The technical difficulties in co-ordinating the signals between the two airframes will also be a major hurdle. As far as the issue of redundancy is concerned, if one of the aiframes is lost, then the other cannot function alone, because the success of the your system depends on two airframes and if one is rendered ineffective, the system loses it functionality. For example, if the processing airframe is lost what will the recce airframe do ? The system therefore does not really cope up with the loss and is not redundant. In systems, such as the EL/M-2060 P, there is a bidirectional datalink which enables near-realtime data transfer between the recce aircraft and a ground station, so even if the airframe is lost after sometime, you atleast have recce data upto the time when the aircraft was in air.

Here are the specs of the ELTA EL/M-2060 P Pod SAR system

GENERAL

The EL/M-2060P is a field-proven high performance reconnaissance system
designed for combat aircraft. The system consists of a detachable pod mounted
Synthetic Aperture Radar (SAR), externally carried by a combat aircraft, a Ground
Exploitation Station (GES) and a built-in bidirectional data link.
The EL/M-2060P produces images which approach photographic quality
and operates as a true all-weather, day and night sensor capable of penetrating
clouds, rain, smoke, and a wide variety of manmade camouflage.

The images produced onboard are transmitted, via the built-in datalink,
to the advanced exploitation station for interpretation and extraction of
valuable Image Intelligence (IMINT) data.

The data is also recorded onboard for retransmission or later interpretation
on the ground.

Operational Features
Realtime SAR Imagery generation

Long ranges and wide area coverage

Ground Moving Target Identification and (GMTI)

Efficient imagery exploitation and reporting

Flexible mission planning, management and realtime mission retasking

Self-sufficient autonomous system, does not require modification of the

host aircraft and does not limit its flight envelope

Minimal pilot workload for system operation

Suited to operation and maintenance by the standard squadron
organization

Modes of operation

STRIP Mode

Fast coverage of large areas at stand-off ranges

Mapping detail sufficient for target detection and overall assessment of
an entire region

SPOT Mode

Detailed examination of designated areas of interest

High resolution for target classification

Strip/Ground Moving Target Indication (GMTI)

Highlights moving targets within the SAR Strip

Characteristics

Aircraft Installation
Physical Characteristics
Weight 590 Kg. (1,310 lb.)

Aircraft Interfaces
Power supply 4.3 kW max (3.5 kW typical)
Self sufficient cooling system

Video Output RS - 170 (05 CCIR)

Command & Control Bus MIL-STD-1553

Ground Exploitation Station (GES)

Advanced data processing software
and friendly operator Man-Machine Interface (MMI)

Provides computer aided tools for data exploitation and intelligence
reporting

Configurable for fixed facility or mobile shelter

Data Link

Full-duplex capability

More than 250 NM Air-to-Ground range, depending on aircraft altitude
and radio line of sight
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Re: Synthetic aperture radar for the IAF

Post by Aditya_M »

Long back I found the ES 310 (US) Naval Weapons Engineering on FAS.

Here is the link that talks about High Res Radar - somewhere down the page you will find Synthetic and Inverse Sysnthetic Aperture Radar (SAR & ISAR).

ES310 is also good for basic radar info, and basics on communication...
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Re: Synthetic aperture radar for the IAF

Post by Rudra »

I posted a link on another thread which claims india plans the EL2060 on M2K. any tactical strike squadron would benefit.
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Re: Synthetic aperture radar for the IAF

Post by vishal »

Originally posted by Jai SR:
As far as the issue of redundancy is concerned, if one of the aiframes is lost, then the other cannot function alone, because the success of the your system depends on two airframes and if one is rendered ineffective, the system loses it functionality. For example, if the processing airframe is lost what will the recce airframe do ? The system therefore does not really cope up with the loss and is not redundant.
Jai,

The redundancy I had in mind was based on the assumption that there would be more than one airframe each for the emitter & processor. Suppose you have 3 airframes of each and one of either is lost. You have still retained part of your capability and can/should still manage a higher mission & serviceability rate than if you had 3 airframes with the complete package and then lost one of them.

I agree on the logistical & technology (communication, synchronization etc) challenges but it seems to be more of a call between approaches an agency/force might want to take.
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Re: Synthetic aperture radar for the IAF

Post by Div »

Don't the IAF or RAW also operate a few Gulfstream SRA's with a SLAR?
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Re: Synthetic aperture radar for the IAF

Post by b_ravi »

Originally posted by Vick:
What kind of radar will the RISAT have?
The RISAT will carry a C-band Synthetic Aperture Radar or SAR.

http://www.isro.org/rep2003/Webpgs/pg17.htm
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