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Radar GMTI
milstar: GMTI Radar Minimum Detectable VelocityJohn A. RichardsSensor Exploitation Applications Department Sandia National Laboratories Minimum detectable velocity (MDV) is a fundamental consideration for the design, implemen-tation, and exploitation of ground moving-target indication (GMTI) radar imaging modes. Allsingle-phase-center air-to-ground radars are characterized by an MDV, or a minimum radialvelocity below which motion of a discrete nonstationary target is indistinguishable from the rel-ative motion between the platform and the ground. Targets with radial velocities less than MDVare typically overwhelmed by endoclutter ground returns, and are thus not generally detectable.Targets with radial velocities greater than MDV typically produce distinct returns falling out-side of the endoclutter ground returns, and are thus generally discernible using straightforwarddetection algorithms. This document provides a straightforward derivation of MDV for anair-to-ground single-phase-center GMTI radar operating in an arbitrary geometry This work was funded by the United States Air Force Electronic Systems Center. Ground moving-target indication (GMTI) radar imaging modes enable the remote detection andcharacterization of nonstationary objects [3, 2, 1]. GMTI data is derived from range-Doppler mapsof the imaged scene, in which reflectivity is measured as a function of rangerand range ratedr/dt(i.e., the radial velocity of an imaged object with respect to the radar platform). All single-phase-center radar air-to-ground GMTI modes are characterized by a minimum detectable velocity(MDV)—more precisely, a minimum detectableradialvelocity, or a minimum detectable rangerate—below which motion of a discrete nonstationary target is indistinguishable from the relativemotion between the platform and the ground. Targets with radial velocities less than MDV aretypically overwhelmed by endoclutter ground returns, and are thus not generally detectable. TheMDV for a particular radar imaging scenario is a function of numerous parameters, including: •Platform velocityv, relative to the ground; •Platform altitudeh, relative to the ground at scene center; •Antenna elevation two-sided beamwidthβe; •Antenna azimuth two-sided beamwidthβa; •Imaging depression angleθto scene center; •Imaging squint angleψ(whereψ=0◦indicates a directly forward-looking geometry); •Slant-plane range-bin spacingδr; •Number of range bins in the image Nr.These parameters impact MDV because they dictate the extent of the imaged scene on the groundand the relative motion of different ground points across that extent, as described shortly. Thecollective set of all imaged ground points comprises the endoclutter.Figure 1 depicts an arbitrary imaging geometry involving level platform motion over levelground. This imaging geometry is completely characterized by the anglesθandψ, the platformheighth, and the platform velocityv. The scene centeristakentobethegroundlocationpointedat by the sensor boresight. https://prod-ng.sandia.gov/techlib-noauth/access-control.cgi/2011/111767.pdf https://icerm.brown.edu/materials/Slides/sp-f17-offweeks/Discussion_of_Radar_and_Moving_Targets_%5d_Armin_Doerry,_Sandia_National_Laboratories.pdf GMTI normally does not display the range-Doppler map as a data product.Rather, the range-Doppler map is an intermediary product on the way to an automatic detection system. The GMTI product is typically just ‘detection reports’ with suitable metadata (e.g. RCS estimate, closing velocity, estimated physical location, etc.).Detections are then simply displayed on a map,sometimes color-coded, or tagged with metadata,often with tracking (time-history) information. ------------- http://ausairpower.net/sargmti-intro.html SAR/GMTI - A Revolution in Bombing Technology Carlo Kopp First published in Australian Aviation June, 1997 The last decade of the twentieth century has seen a number of technological paradigm shifts in air warfare - Stealth, GPS guided weapons, super-manoeuvrable fighters, agile dogfight missiles, active radar medium range missiles and a number of developments in radar. Of the latter perhaps the most significant yet least publicised has been the development and early deployment of reconnaissance, surveillance and attack radars incorporating high resolution imaging Synthetic Aperture Radar (SAR) and Ground Moving Target Indicator (GMTI) techniques. This technology promises to revolutionise battlefield and strategic bombing operations, and combined with the GPS guided bomb will displace the established thermal imager/laser designator and laser guided bomb within the next decade. ######## http://www.helitavia.com/skolnik/Skolnik_chapter_17.pdf TABLE 17.1 Pulse Doppler Applications and RequirementsTABLE 17.2 Comparison of MTI and Pulse Doppler (PD) RadarsPulse Doppler Spectrum. MTI- low PRF --------------------- Advantages Can sort clutter from targetson basis of range. No rangeghosts. Front-end STC sup-presses sidelobe detectionsand reduces dynamic rangerequirements Disadvantages Low doppler visibility due tomultiple blind speeds. Poorslow-moving target rejection.Cannot measure radial targetvelocity. PD- medium PRF --------------------------- Advantages Good performance at all tar-get aspects. Good slow-moving target rejection.Measures radial velocity.Less range eclipsing than inhigh PRF. Disadvantages Range ghosts. Sidelobe clut-ter limits performance. Highstability requirements due torange folding. PD- high PRF ------------------------ Advantages Can be sidelobe clutter-freefor some target aspects. Sin-gle doppler blind zone atzero velocity. Good slow-moving target rejection.Measures radial velocity.Velocity-only detection canimprove detection range. Disadvantages Sidelobe clutter limits perfor-mance. Range eclipsing.Range ghosts. High stabilityrequirements due to rangefolding.
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milstar: SAR/GMTI - A Strategic Perspective State of the art high resolution imaging Synthetic Aperture Radars can produce spot maps of areas hundreds of metres to kilometres in size at tens of NMI of range, with resolutions at this time as fine as one foot. In the simplest of terms, you can use such radars to produce geometrically accurate surface maps in which the smallest feature size is a foot. Therefore buildings, roads, structures, vehicles, parked aircraft, ships, fences, radio masts, radar antennas and any other features of interest can be detected, identified and accurately located in relation to the surrounding terrain. State of the art Ground Moving Target Indicator radars can detect slowly moving surface vehicles, taxiing aircraft, and hovering helicopters. In many instances, these radars can also exploit fine Doppler modulations in the radar return to identify the vehicle class or type, and even rotating radar antennas. A radar which combines these two technologies can accurately detect, locate and identify virtually any surface target, from a standoff range at a very shallow slant angle, under any weather conditions. Combined with GPS guided bombs, this is a revolutionary capability, because it extends the existing around the clock bombing capability to an all weather standoff bombing capability. The established thermal imaging/laser guided bombing technology requires that direct line of sight exists to the target, that the cloudbase is above the bombing aircraft, and that the humidity and precipitation situation is not severe. Many bombing sorties were aborted during the Gulf War as these conditions were not satisfied. Moreover getting close enough to the target to use a thermal imager exposes the aircraft to air defences. In strategic bombing operations, the use of SAR/GMTI capable radars and GPS guided weapons will allow any strategic target to be bombed under any conditions, with no loss in accuracy. If glidebombs or standoff missiles are used, air defences can be bypassed with no loss in accuracy. Because the radar can cover a much larger footprint than a thermal imager, and GPS guided weapons are wholly autonomous once released, multiple aimpoints can be engaged on a single pass. This means a from one aircraft - one target to one aircraft - many targets. It we further factor in programs such as the USAF MMTD (Miniature Munition Technology Demonstration) or small bomb program, which aims to produce a 250 lb differential GPS guided bomb with the lethality of a Mk.84 2,000 pounder and a CEP of about 5 feet, we end up with a massive increase in the potency of Western air power. Fully loaded with such weapons an F-111 or F-15E acquires the killing power of a B-52 loaded with conventional Mk.84s. Attacks upon convoys and road and rail communications deep inside hostile airspace can be conducted under any weather conditions, and surface targets of opportunity can be easily detected. Traditionally such strikes were concentrated upon choke points such as bridges, in turn this predictability gave a defender the opportunity to preposition defences. With a SAR/GMTI capable attack radar, a bomber can sweep highways and railroad lines for traffic and accurately engage that traffic once detected. In defence suppression (SEAD) operations mobile radar, SAM and AAA systems have been traditionally difficult to locate, particularly if the operators are clever and only transmit intermittently, between moves. With SAR/GMTI radar, such targets can be detected and engaged on the move. If the capability exists to detect rotating antennas, then non-emitting rotating antenna radar targets can be found and bombed. In Battlefield Air Interdiction (BAI) and Close Air Support (CAIRS) operations, moving armour and supply convoys can be readily detected and engaged on the move, again under any weather conditions. Submunition dispensing glide weapons such as the JSOW or its European cousins are specifically designed for this purpose. Indeed the JSTARS controlled ambush of the Iraqi relief column to Khafji was the precursor of what will become a more general style of BAI ops. In reconnaissance operations large areas can be mapped without the need to overfly the area of interest, thereby both alerting an opponent to your interest in the area, as well as exposing the recce aircraft to hostile fire. Because a capable SAR/GMTI sensor can overlay GMTI tracks over accurate SAR maps, activity in the area of interest becomes much easier to detect and interpret. Inclement weather is no longer the restriction it used to be for recce sorties using optical and thermal imaging cameras or linescanners. In surveillance operations, a platform with a capable SAR/GMTI radar can become like the E-8 JSTARS, a land warfare analogue to the AWACS/AEW&C, with the capability to look up to 200 NMI deep into hostile airspace to detect and track vehicular activity. The all weather standoff capability of the radar, combined with a good onboard C3 package, will allow such aircraft to vector fighters onto hostile surface contacts. In littoral maritime operations, supporting amphibious operations, suppressing coastal defences, softening up for strikes or bombardment and extracting surface forces, radars with a SAR/GMTI capability can be employed to locate small surface combatants hidden from ship borne radars by terrain, as well as to locate coastal defences, and movements of defensive equipment. Air warfare strategists recognise the important concept of the targeting cycle. This cycle involves the detection, location and identification of targets, followed be the engagement of these targets, and post strike bomb damage assessment (BDA) to determine whether reattack is required. During the Gulf War this cycle was often contracted down to hours, but more typically involved 24 to 48 hours for strategic targets. The most revolutionary change which the wide deployment of SAR/GMTI capable radars will bring is the contraction of the targeting cycle. Targets can be detected, located, identified, engaged and damage assessed in a matter of minutes. The targeting cycle is then contracted down to a look-shoot-kill-look cycle, all under arbitrary weather conditions and at standoff ranges, if suitable munitions are used. Historically, surface bound opponents have often evaded air attack through clever use of mobility and exploitation of foul weather. Whether we look at the Wehrmacht retreat up the Italian peninsula, or the Ardenne offensive, or interdiction operations in Korea and Vietnam, or Scud hunting in the Gulf, in every instance Western air superiority did not convey the ability to nail every hostile surface asset (something which air power opponents never fail to mention). The refuge of mobility and foul weather disappears once SAR/GMTI radars are widely deployed. There is no escape, if it moves it is found and killed. If it doesn't move it is a useless asset. The combination of all weather operation, precision and rapid response times is the most revolutionary change in air power ever brought about by a single technological step. And this is a step which involves a modest cost indeed as the new generation of radars will be similar in cost in existing technology, while the GPS guided bombs are similar in cost to bottom of the range laser guided bombs. The combined effect of this sensor and weapons technology will be to increase the lethality of any single combat aircraft by a factor of five to ten. It is worth noting that with continuing budgetary pressures to downsize being applied to Western fighter and particularly bomber fleets, this technology is essential if Western air power is to maintain its pre-eminent position in the World. It does mean that a credible combat capability can be retained even if force sizes are further contracted. In practical terms it means that a stealthy lightweight fighter just as the JSF can still have the lethality of an F-16 or F-18 carrying internal weapons, and that a top tier fighter such as the F-22 can have the lethality of an F-15E or F-111 while carrying internal weapons. What does not change in this equation is that you still need a big aeroplane to go a big distance, Breguet's equation cannot be escaped. A small lightweight JSF will still not be able to perform the deep strike mission of the F-111 or F-15E simply as the basic range requirement forces a bigger airframe. Therefore if you want to replace an F-111, F-15E or F-117A with a comparable deep strike fighter, you need something of a similar size and weight, ie an F-22 or similar. By the same token if you want to replace a B-52 you will need something of a similar size (eg B-2). What the small bomb technology does allow is stealth with lesser difficulty in packaging lethality into the available volume, so that designers are not faced with the dilemma of the A-12 Avenger which died because it ended up with so many internal bomb bays that the engineers had to beef up the internal structures and compromise weight and thus overall performance. The other side of this issue is that some targets such as large factory complexes, warehouses and troop formations dug in on the battlefield will be best attacked by carpeting them with dumb bombs, even if these will be "small bombs". Therefore attacking such targets will require a hefty payload. Other issues which do not change are the requirement for aircrew skills in operating such systems. If you have an onboard SAR/GMTI radar and a dozen bombs with which to hit 6 intended aimpoints, the operator must be capable of identifying the aimpoints in the cockpit imagery correctly and designating them to the nav-attack computer so the bombs can be programmed with aimpoints before release, all within the timeframe within which he would engage a single target using established laser guided weapons and Flir sensors. To fully benefit from the technology a dedicated navigator/WSO may still be required, again mitigating against lightweight single seaters. Survivability of the aircraft will continue to be an issue, moreso since increasing lethality will make them more valuable targets to an opponent - we can expect even more effort to be expended on air defences given that a single aircraft can do vastly more damage per unit than existing systems can. Stealth and stand-off range will be essential. In the light of the above, it appears that stealth will become an inevitable necessity if munition costs are to be kept to a minimum (eg dropping JDAM and MMTD vs JSOW and standoff missiles). The electronic warfare threat to radar and GPS will always exist. However, the most recent generation of GPS receivers has a significant anti-jam capability, and modern radars are built from the ground up with robust ECCM performance. In any event the successful use of countermeasures against modern radar and GPS alike requires a considerable degree of technological and operational sophistication. The required level of sophistication is yet to be seen in the wider Asia-Pacific region, and certainly will not be seen in SEA in the forseeable future. Because potential opponents have more to gain from exploiting Western GPS than jamming it, it is fair to say that the credibility of the "GPS is vulnerable to jamming" argument is often greatly overstated (mainly by opponents of air power). In summary it must be reiterated that current developments in SAR/GMTI radar, combined with GPS and Differential GPS guided small bombs represent the most significant gain in bombing capability seen since the deployment of the laser guided bomb and thermal imager. Unlike the former, which had important weather related limitations, SAR/GMTI radars and GPS guided bombs suffer none of these. The radar technology is now operationally deployed with the USAF, USN and Israeli Air Force, and the GPS guided bomb is now operational with the USAF. All of these are services with a proven recent combat track record and the experience and judgement to realistically assess that which works and that which doesn't. The consensus is evidently that the technology works robustly, as major expenditure has been allocated to deploying these technologies on a wide scale. In the Australian context this technology should be of great interest to the RAAF, given the humid and wet climatic environment in the Deep North and SEA, which is not conducive to getting good performance from 10 micron band thermal imagers such as the Pave Tack. Combining this with monsoonal weather means that thermal imagers and thus laser guided weapons are subject to weather related no-go situations far more frequently than in the temperate Northern Hemisphere. Equipping the F/RF-111C and F-111G with a suitable SAR/GMTI radar and GPS/DGPS guided bombs/glidebombs would remove this limitation completely, providing the RAAF with an unrestricted all-weather around the clock precision or accurate bombing capability, while reducing aircraft exposure to point defence weapons. The RAAF should give serious consideration to the wide adoption of this technology, and should mooted upgrades to the F-111G proceed, equip these aircraft first. An F-111G with a SAR/GMTI capable attack radar and four to six JDAMs is a formidable and highly cost effective bombing capability, whether applied to strategic bombing or Army support operations. Arguably in the latter role much more is to be gained, given the more dynamic targeting environment. The ADF has dithered far too long on the operational deployment of this technology, moreso given the superb results from DSTO's work in this area. Clearly the Minister should move decisively at the earliest possible time, override if necessary any DoD bureaucratic obstruction, and proceed to operational deployment by the turn of the century. Not to do so is to do the taxpayer a disservice. A future feature will discuss the radar technology in more detail, including some representative radars. http://ausairpower.net/sargmti-intro.html
milstar: Ground Moving Targets in SAR ImageryOutline •Nominal Moving Target Phase Equations•Measured Moving Target Phase Examples•Space Time Adaptive Processing (STAP) Review•STAP applied to 8 channel SAR image data (element space, phase centers)–Single 3 sec coherent integration full azimuth resolution –Ten 0.3 second coherent integration times, results in SAR movie of moving vehicle http://helper.ipam.ucla.edu/publications/sar2012/sar2012_10417.pdf • Quadratic phase defocuses Doppler/azimuth IPR• Formula for quadratic expressed for polar format processed data • Target energy can be focused by phase compensation • Stationary Targets do not exhibit 1000’s deg of phase Note: GMTI•Show examples of common processing of multiple channel radar data into image and moving target products–Long coherent dwell (e.g., 2 to 3 seconds)–Subdivision of dwell into short coherent processing intervals (e.g., 10 CPIs each 0.2 seconds duration) •Data observations and discussions –MTI with and without clutter suppression –Target range acceleration and cross range velocity provides phase characteristics not shared stationary targets•Energy migration through freq bins, intrinsically more degrees of freedom to match signal, signal processing implications•Also hedge against false alarms
milstar: Ground/Dismount Moving Target Indicator The GMTI mode provides a quick and easy method for locating moving vehicles. While the GMTI mode continues to be a crucial resource, DMTI marks a real paradigm shift. DMTI allows operators to detect very slow moving vehicles and personnel (dismounts) moving at about 1 mph. Integrated into USAF MQ-9 Reaper® RPA, the DMTI mode allows operators to detect slow-moving, operationally significant personnel or vehicles. In addition, operators can select a GMTI/DMTI target and automatically cross-cue to the EO/IR sensor in narrow FOV for visual identification of the target. https://www.ga-asi.com/radars/lynx-multi-mode-radar
milstar: MIT Lincoln LaboratoryRadar Course_36.pptODonnell (2) 6-19-02Summary• Moving Target Indicator (MTI) techniques– Doppler filtering techniques that reject stationary clutter• No velocity measurement– Blind speeds are regions of Doppler space where targets with that Doppler velocity cannot be detected• Changing the PRF between sets of pulses can alleviate the blind speed problem– MTI techniques have a limited capability to suppress rain clutter• Pulse Doppler techniques– Used to optimally reject various forms of radar clutter• Measurement of target radial velocity• Moving Target Detector techniques are an example of optimum Doppler processing and associated adaptive thresholding– Ambiguities in range and Doppler velocity can be resolved by transmitting multiple bursts of pulses with different PRF’s– Airborne radars use multiple PRF waveforms to suppress clutter https://www.ll.mit.edu/sites/default/files/outreach/doc/2018-07/lecture%208.pdf
milstar: https://electronics-club.com/moving-target-indicator-mti-radar/
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