Directed Infrared Countermeasures Research Articles

Analysis of finite energy fresnel bessel beams scintillation level in turbulent communication links

Scintillation indices of Finite Energy Fresnel-Bessel Beams (FEFBBs) propagating for 6 Km in a turbulent atmosphere are analyzed. In this context, the effects of beam order and Gaussian beam waist on the reduction of scintillation level are evaluated. Both the point-like scintillation and the power scintillation indices are examined. The obtained results show that beam order does not have a significant impact on the scintillation levels. FEFBBs are able to reduce the power scintillation levels, then improve the system performance better than fundamental Gaussian beams. Thus, the provided results are significant for not only the performance improvement of the free-space optical (FSO) communication systems but also for the applications that require line of sight alignment namely directed infrared countermeasure (DIRCM).

Derivation of Rytov variance for jet engine-induced turbulence

In this study, we analytically derived the Rytov variance and scintillation index value of turbulence caused by jet engines. In addition, we analyzed the variation characteristics of the Rytov variance and scintillation index values numerically depending on the variations in turbulence strength, experimental data, and wavelength. We observe that Rytov variance reaches up to high values due to the strong turbulence resulting from high refractive index fluctuations. This result brings high-intensity fluctuations regardless of the anisotropy of the turbulence. Rytov variance is directly proportional to turbulence strength. We present scintillation index curves considering the aperture averaged case. We plot our results considering the variations in the operating wavelength, turbulence strength, and the scaling parameter. According to our results, we think that it will be useful for a system such as directed infrared countermeasure (DIRCM), which is highly sensitive and should be exposed to minimum turbulence in the field of use. Since DIRCMs transmit codes to paralyze the missile’s seeker, intensity fluctuations play a vital role during this transmission. It could reduce the performance of these systems when intensity fluctuations are high.

A study of effects of a turbulent jet engine exhaust on partially coherent Laguerre-Gaussian Schell model vortex beam

In this study, based on the generalized Huygens-Fresnel principle, the evolution properties, such as spectral density, degree of coherence, and beam width of the propagation of partially coherent Laguerre-Gaussian Schell model vortex beam (PCLGSMvB) in jet engine exhaust are studied. Our results show that the spectral density of the corresponding beam can change their form shape during its propagation as the source coherence varies. When the source coherence width is high, the profile of PCLGSMvB changes from initially dark hollow into two spot beams at short propagation distances. If the source coherent width is very small, the shape of PCLGSMvB is converted to a Gaussian shape and keeps its form upon propagation. Also, we found that the spreading of PCLGSMvB is related with their initial parameters, and it will be spread faster with smaller source coherence width, larger mode order n, and longer wavelength. Furthermore, the beam width of the PCLGSMvB increasing as the structural constant increases and it means that the beam can resist to stronger fluctuation of turbulence. Outputs of this study has potential application on deriving the requirements of optical systems on aircrafts like laser range finder, laser designator, optical communication systems and directed infrared countermeasure (DIRCM).

Analysis of Open-Loop DIRCM Jamming Effects on First Generation Infrared Seekers

The Directed Infrared CounterMeasure (DIRCM) is an infrared countermeasure that is employed against different kinds of infrared missiles. Its purpose is to make missiles miss the target, by jamming their infrared reticle seekers or by dazzling the imaging seekers. In this manuscript, we developed a software in MatLab which simulates three different infrared first-generation seekers, to evaluate DIRCM’s jamming effects on signal processing and in target tracking. Using three different reticles, it’s noteworthy the influence of some of the DIRCM’s parameters, such as pulse repetition frequency (PRF) and intensity. The highest jamming efficiency is achieved when its PRF is close of the seeker’s reticle spinning frequency. In order to evaluate the effects of an open loop DIRCM, a composite DIRCM jamming waveform was modeled and tested against the three different modeled seekers. This approach achieved the optical break lock in all three seekers in less than 0.7 seconds.

Propagation of hyperbolic sinusoidal Gaussian beam in jet engine induced turbulence

This paper investigates beam evolution and beam sizes variation of hyperbolic sinusoidal Gaussian (HSG) beam propagating in jet engine exhaust-induced turbulence. We find the received field by solving Huygens-Fresnel integral with a relevant power spectrum. Our results reveal that HSG loses its initial profile until 100 m. Besides, beam with low displacement parameter value is more resistive against turbulence. In terms of beam size, beams with low Gaussian source size expand less as compared to the beams with larger Gaussian source size. In the light of our findings, optical systems in aircrafts like directed infrared counter measure (DIRCM) and laser designators can be developed.

Near field propagation of hollow higher-order cosh-Gaussian beam in jet engine induced turbulence

Propagation of hollow higher-order cosh-Gaussian (HHOCG) beam through jet engine induced turbulence is analyzed in this article. Special form of Huygens–Fresnel integral is solved in order to find averaged received intensity. Since beam shows rapidly focusing behavior, intensity profile is analyzed for short propagation distances. Beam evolves into four petal shape at short distance and size of hollow in the center is directly proportional with beam parameters. Raise in these parameters brings longer focusing point along propagation axis. Surprisingly, beam shows focusing behavior along propagation. According to our results, we think that especially this focusing trend is useful for applications required line of sight alignment like directed infrared counter measure (DIRCM).

A Missile Jamming Design for Aircraft Defence Using Infrared Automated Counter Measures

Infrared guided missiles possess a greater threat towards aircrafts in the scenario of defence. Securing aircrafts from such attacks requires an active directed infrared counter measure. Since DIRCM systems require the parameters of the missile signals to be known in advance, they suffer when attempted to be applied in real time. This paper proposes anInfrared Automated Counter Measures (IRACM) system with an equippedmissile alert equipment (MAE) capable of estimating the signal parameters once the signal is detected. Jamming is performed by which the missiles are subjected to miss the target along the field of vision by updating the jammer frequency based on the signal parameters. Since IR flashes in IRACM are emitted directly towards the missiles, it is considered more efficient when compared with the flare methods which emits in all directions. The experimental results of proposed method reveal that the system performs well in estimating missile signal parameters and the jamming effect is influenced by the estimated parameters.

Investigation of the influence of optical turbulence on DIRCM laser’s jamming effectiveness: A wave-optics approach

Due to their exceptionally large jam-to-signal ratios (J/S), Directed Infrared Countermeasure (DIRCM) systems are the most efficient means for defeating heat seeking missiles. Although many studies have investigated DIRCM systems, the influence of optical turbulence on the jamming code effectiveness is mostly ignored. However, due to optical turbulence caused by the exhaust plume of the air platform and the atmosphere, a DIRCM laser’s beam may be exposed to time-varying intensity fluctuations, which may dramatically reduce the effective J/S at the seeker’s aperture compared to the one at the platform. In addition, previous studies have generally focused on the signal processing stages of seeker heads while ignoring diffractive and aberrative properties of the missile optics. In this study, we employ a wave-optics approach for estimating the jamming code effectiveness under turbulence. Specifically, we investigate time-varying influence of several degrees of optical turbulence on DIRCM laser beams with specified beam quality factors (M2) that are modulated with various jamming patterns. In our model, the DIRCM laser beam first passes through a highly turbulent region, which is caused by the rotor downwash of the exhaust plume of a rotary-wing platform. Next, the DIRCM laser beam propagates in an atmospheric turbulence region for much longer distances (on the order of few km’s) until it reaches the missile. Laser beam propagation in both turbulence regimes is simulated using the split-step method. Subsequently, using the ZEMAX software and its wave-optics-based Physical Optics Propagation (POP) package, we employ a generic model for the optical system of a first-generation spin-scan seeker and obtain the time-dependent intensity profiles of the laser beam at the focal point. Generic models for an uncooled lead-sulfide detector and the following signal processing stages have also been included in the model.

Modeling the Electro-Optical Performance of High Power Mid-Infrared Quantum Cascade Lasers

Performance modeling of the characteristics of mid-infrared quantum cascade lasers (MIR QCL) is an essential element in formulating consistent component requirements and specifications, in preparing guidelines for the design and manufacture of the QCL structures, and in assessing different modes of operation of the laser device. We use principles of system physics to analyze the electro-optical characteristics of high power MIR QCL, including thermal backfilling of the lower laser level, hot electron effects, and Stark detuning during lasing. The analysis is based on analytical modeling to give simple mathematical expressions which are easily incorporated in system-level simulations of defense applications such as directed infrared countermeasures (DIRCM). The paper delineates the system physics of the electro-optical energy conversion in QCL and the related modeling. The application of the performance model to a DIRCM QCL is explained by an example.

Numerical laser beam propagation using large eddy simulation of a jet engine flow field

In certain directed infrared countermeasure (DIRCM) situations, the laser beam path may have to pass close to the engine exhaust plume of the aircraft and models of plume turbulence are needed for DIRCM performance simulations. The jet engine plume was modeled using large eddy simulation (LES), providing time resolved information about the large scale turbulent eddies. The refractive index data from the LES calculations were integrated along the propagation path to produce time resolved phase screens for optical beam propagation. The phase screens were used to calculate laser beam parameters including beam wander and power-in-bucket (PIB). Numerical beam propagation resulted in a root-mean-square beam wander of 200 μrad for the small turbojet engine studied. The PIB was calculated for beams with 80 μrad and 2 mrad divergence having equal beam diameter when passing through the plume. For the beam with low divergence, the average PIB was reduced from 0.23 to 0.040, while the beam with wider divergence showed no significant reduction. In both cases, the plume introduced significant temporal variation of the instantaneous PIB. The beam wander is not affected by the divergence, but only depends on beam size.

Modeling and Simulation of the Active Jammer Effect in the Crossed Array Detectors Infrared Seeker

IR active jammers or the directed infrared counter measures(DIRCM)generate IR signals which attack the guidance signals passed to the sensors in IR-guided weapons. They provide IR signals with appropriate frequency, phase and intensity which will be superposed on those produced by the IR energy of the target passing through the reticle. When both the jamming signal and the modulated target energy signals are received by the missile‟s IR sensor, they cause the tracker to produce incorrect guidance commands and push the target out of the field of view (FOV). In this paper, the seeker signals of a crossed four slits or crossed array detectors (CAT) infrared seeker will be simulated. Then the active jammer signal is modeled and simulated. After that, the effect of all the active jammer parameters will be discussed and simulated. Finally, the conditions or the ranges of these parameters in which the active jammer can affect the seeking process will be stated.

Jamming effect analysis of infrared reticle seeker for directed infrared countermeasures

In directed infrared countermeasures (DIRCM), the purpose of jamming toward missiles is making missiles miss the target (aircraft of our forces) in the field of view. Since the DIRCM system directly emits the pulsing flashes of infrared (IR) energy to missiles, it is more effective than present flare method emitting IR source to omni-direction. In this paper, we implemented a reticle seeker simulation tool using MATLAB-SIMULINK, in order to analyze jamming effect of spin-scan and con-scan reticle missile seeker used widely in the world, though it was developed early. Because the jammer signal has influence on the missile guidance system using its variable frequency, it is very important technique among military defense systems protecting our forces from missiles of enemy. Simulation results show that jamming effect is greatly influenced according to frequency, phase and intensity of jammer signal. Especially, jammer frequency has the largest influence on jamming effect. Through our reticle seeker simulation tool, we can confirm that jamming effect toward missiles is significantly increased when jammer frequency is similar to reticle frequency. Finally, we evaluated jamming effect according to jammer frequencies, by using correlation coefficient as an evaluation criterion of jamming performance in two reticle missile seekers.

Fast Model Predictive Control of the Nadir Singularity in Electro-Optic Systems

RECISION pointing and stabilization of the sightline are vital capabilities in all airborne electro-optic (EO) equipment. In traditional control theoryterminology,the pointingtask isatracking requirement,eitherofadynamictargetorsomeotherspecialpointof interest, and stabilization refers to the disturbance rejection capability of the sightline controller; typical disturbances are a combinationofownshipmotionandbearingfriction. Therelativeimportance between the pointing and stabilization tasks is a function of the intendedoperationoftheEOsystem;forexample,long-rangetargetingrequiresprecisestabilization,butanagilesightlineisessentialfor directed infrared countermeasures (DIRCM) systems [1], although both pointing and stabilization loops should be optimized for all systems. A DIRCM engagement occurs when the host platform is attacked by a surface-to-air missile, usually a shoulder-launched Man-Portable Air Defence missile, which is defeated when the DIRCM system positions a jamming signal onto the missile seeker. Obviously, accurate target tracking is essential over a full hyperhemispherical field of regard (FOR), as any tracking deficiencies are sure to be exploited by future missile guidance systems and tactics. Given the particular threat of global terrorism to the airline industry, future DIRCM systems should be small, lightweight, and costeffective for inclusion on commercial aircraft, which invariably limits the number of available axes for sightline control. A minimum of two axes are necessary to attain full hyperhemispherical FOR. The outer gimbal (OG) axis is usually constrained to rotate with respect to the platform z axis (through azimuth angle � ) and the inner gimbal (IG) with respect to the OG y axis (through elevation angle ). This is shown in Fig. 1. When the outerandinneraxesareorthogonal,thesightlinecanbepositionedto any orientation in space, as the IG and OG axes form an ideal orthogonal basis. However,whenthe innergimbal angleapproaches the nadir (defined as �� 90 deg) (i.e., the sightline becomes aligned with the axis of rotation of the outer gimbal), the pointing system experiences the loss of a degree of freedom known as gimbal

Laser dazzling of infrared focal plane array cameras

Modern weapons systems often use infrared imaging for acquisition and tracking of targets. In the acquisition phase, the operator uses the system to detect the target and aim the weapon. In the tracking phase, the images from the camera are used to guide the weapon to the target. One possible method of protection against such imaging systems is laser dazzling. The intended effect is to deny the imager a clear view of the target by saturating the detector and consequently preventing the weapon from making a hit. The problem of locating the threat and pointing the laser at it is closely connected to the countermeasure effectiveness. This has been investigated particularly for specific applications such as directed infrared countermeasure (DIRCM) systems for aircraft self-protection. Another application is sniper detection, which uses the ‘cat’s-eye’ or retro-reflection effect, which occurs when a searching laser beam is directed at the visor of the rifle. We currently aim to use the retro-reflection effect in a wider range of applications for locating optics.1 The aim of our dazzling work is to quantify the effects of laser countermeasures on mid-wave infrared (MWIR) imaging to predict the decrease in the detection and pointing capabilities of weapons systems. Dazzling with a continuous or quasicontinuous pulsed laser causes a reversible saturation effect on the detector array. Most of the current MWIR lasers provide output power levels that do not exceed saturation levels for practical applications. Permanent damage effects require much higher irradiance levels at the camera front optics. This might be within reach at shorter ranges with these lasers, but is not addressed in our current research. In our experiments we used a periodically poled lithium niobate optical parametric oscillator (PPLN OPO) laser pumped by an Nd:YVO4 (yttrium orthovanadate) laser to generate a 3.9μm laser wavelength.2 Figure 1 presents images of a standard 256×320 indium antimonide (InSb) camera irradiated by Figure 1. Impact of increasing laser irradiance on the InSb camera image.

Performance of laser tracking of small targets during turbulence and beam jitter

Small target detection and tracking are important for laser radars in many applications such as laser weapons, directed infrared countermeasures (DIRCM), fire control, target recognition, and free-space laser communications. The detection and tracking performance depends on the mode of detection, SNR, target signal statistics, beam jitter, and turbulence induced irradiance variations. We show results of the root mean square (rms) tracking error versus SNR primarily for direct detection systems using a strong glint return. For the general case of a certain signal and noise probability density functions (pdf) it is hard to obtain analytical solutions for the mean and variances of the estimates for the rms tracking error. We have therefore used numerical simulations to illustrate how the pdf and SNR will affect the tracking accuracy. Gamma functions and other pdf's can be used to characterize the signal distributions to get a first hand on tracking performance. The results are presented as tracking errors versus the angular spot size of the laser beam in the tracking detector plane. We also investigate the beam optimization problem for target detection and "power in bucket," which is maximizing the laser energy at the target. We find that there are optimum beam sizes (w) versus the rms jitter () and that optimum w/ (minimizing the false alarm rate for a given detection probability Pd) typically fall in regions 1 to 3 depending on probability of detection and the representative pdf for the application in mind.