IR Scene Research Articles

Infrared scene projector (IRSP) for cryogenic environments based on a light-driven blackbody micro cavity array (BMCA)

An infrared scene projector (IRSP) that can operate at an ambient temperature lower than 190 K is developed for the hardware-in-the-loop (HIL) simulation of space-borne IR detection systems. The IRSP is composed of a visible scene generator (VSG), a visible to IR converter, and an IR projection system optimized for cryogenic environments. The core component of the IRSP is a light-driven blackbody micro cavity array (BMCA). The BMCA is a photothermal conversion device. It can transform visible light images into IR images. The BMCA can operate properly in an ultralow temperature environment, and the temperature of the BMCA is the same as the ambient temperature. This property allows the BMCA to generate IR scenes with a pure low temperature background, which is crucial for the ground testing of space-borne IR detection systems. The performance of the IRSP was tested in a vacuum cold chamber. In the cryogenic environment with an ambient temperature of 187.75K, the observed highest temperature of the generated IR scene was 426.15 K, the lowest temperature was 187.75 K, the dynamic range of the IR scene was 38.69 db, and the frame rate of the IR scene reached 76 Hz. The average visible to IR conversion efficiency of BMCA was about 10.6%∼3.1% under different ambient temperatures. The radiation spectrum of the IRSP is close to the standard blackbody radiation spectrum both in the MWIR band and the LWIR band. The IRSP has been applied in a HIL simulation test of a space-borne IR detection system.

온도 손실의 최소화를 위해 Sub-Frame 제어 기법을 적용한 적외선 영상 투사기용 신호입력회로

본 논문에서는 30 ㎐의 프레임률로 동작하는 적외선 영상 투사기 (IR scene projector, IRSP)에서 투사되는 적외선 영상의 유효온도 감소를 최소화하기 위해 sub-frame 제어 기법을 적용한 IRSP용 신호입력회로 (read-in integrated circuit, RIIC)를 제안한다. 제안하는 sub-frame 제어 기법은 단위 프레임을 8개의 sub-frame으로 나누어 동일한 영상 데이터를 8회 refresh함으로써 픽셀 내 커패시터에 sampling된 영상 데이터가 유지 기간 동안 MOSFET 스위치를 통한 누설 전류로 인해 손실되는 정도를 감소시킨다. Emitter에서 투사되는 적외선 영상의 높은 유효온도를 위해 전류 구동형 RIIC를 설계하였으며, 외부의 DAC로부터 아날로그 전압 형태의 영상 데이터를 전송 받는다. 시제품 64 × 32 RIIC array 칩은 매그나칩/SK하이닉스 0.35 ㎛ 2-poly 4-metal CMOS 공정으로 제작되었으며, 출력 가능한 최대 데이터 전류는 230.3 ㎂이다. 이를 15 kΩ의 저항 값을 갖는 시제품 emitter 소자에 인가할 시 mid-wavelength IR (MWIR) 대역을 기준으로 최대 366.2 ℃의 유효온도를 갖는 적외선 영상의 투사가 가능하다.

GPU-based high-precision real-time radiometric rendering for IR scene generation

Aiming at the problem that traditional infrared scene real-time radiometric rendering method leads to greater calculation error for securing real-time purpose, this article studies the IR rendering comprehensive optimization method, which secures real-time performance as well as calculation accuracy. Firstly, based on the effective average value principle, the spectrum coupling thermal emission and reflected radiations in the spectral radiometric equation are decomposed into physical quantities, and the spectral radiometric equation is improved to become a simpler calculation between “primer” radiance terms and effective average factors. Secondly, the parameter processing method is proposed to cope with the situation when index parameters of effective average factors exceed the maximum dimensionalities of graphics processing unit (GPU) look-up-table (LUT); and pre-calculation method is applied to promote the real-time evaluation efficiency of the physical quantities in the radiometric equation. Finally, concurrent computation of radiometric equation is achieved with GPU IR scene generation software and the precise and real-time rendering of three-dimensional IR scene is realized.

스트랩다운 적외선 영상센서를 위한 관성센서 기반 강인최소자승 움직임 훼손영상 복원 기법

This paper proposes a new robust motion deblurring filter using the inertial sensor measurements for strapdown image IR applications. With taking the PSF measurement error into account, the motion blurred image is modeled by the linear uncertain state space equation with the noise corrupted measurement matrix and the stochastic parameter uncertainty. This motivates us to solve the motion deblurring problem based on the recently developed robust least squares estimation theory. In order to suppress the ringing effect on the deblurred image, the robust least squares estimator is slightly modified by adoping the ridge-regression concept. Through the computer simulations using the actual IR scenes, it is demonstrated that the proposed algorithm shows superior and reliable motion deblurring performance even in the presence of time-varying motion artifact.

관성센서를 이용한 스트랩다운 탐색기 훼손영상 복원기법

본 논문에서는 스트랩다운 영상탐색기 개발을 위해 각속도계 정보를 이용한 실용적인 움직임 훼손영상 복원 필터링 기법을 제안한다. 각속도계 편향오차가 움직임 훼손을 기술하기 위한 점확산 함수 파라미터의 불확실성으로 작용한다는 점에 착안하여, 이를 놈 제한조건을 만족하는 파라미터 불확실성으로 가정한 후 움직임 훼손 영상을 불확정 선형 상태 공간 방정식으로 모델링한다. 각속도계 편향오차에 의한 파라미터 불확실성 행렬이 놈 제한 조건을 만족한다는 가정 하에, 순환 선형 강인 칼만필터에 기반한 움직임 훼손영상 복원필터가 설계된다. 실제 IR 영상을 이용하여 제안된 영상훼손 복원 필터가 각속도계 편향 오차가 존재하는 상황에서도 신뢰할만한 영상복원 성능을 제공함을 확인한다. This paper proposes a practical linear recursive robust motion deblurring filter using the inertial sensor measurements for strapdown image seekers. The angular rate information obtained from the gyro mounted on the missile is used to define the PSF(point spread function). Since the gyro output contains a unknown but bounded bias error. the motion blur image model can be expressed as the linear uncertain system. In consequence, the motion deblurring problem can be cast into the robust Kalman filtering which provides reliable state estimates even in the presence of the parametric uncertainty due to the gyro bias. Through the computer simulations using the actual IR scenes, it is verified that the proposed algorithm guarantees the robust motion deblurring performance.

Thermal Event Recognition Applied to Protection of Tokamak Plasma-Facing Components

Magnetic confinement fusion tokamaks are complex devices where a large amount of power is required to make the fusion reactions happen. In such experimental conditions, plasma-facing components (PFCs) are subjected to high heat fluxes that can damage them. Machine protection functions must then be developed to operate current and future devices like ITER in the safest way. In current tokamaks like Tore Supra, IR thermographic diagnostics based on image analysis and feedback control are used to measure and monitor the heating of the PFCs during plasma operation. The system consists of detecting a high increase of the IR luminance signal beyond fixed qualitative levels for a set of predefined regions of interest (ROIs). The detection of overheating regions is then fully dependent on the settings of the ROIs and of the qualitative thresholds. This ROI-based approach must be improved to fit with ITER requirements and operation, where the IR scene complexity (many components monitored at the same time) will be a real challenge for the real-time PFC protection. In this paper, we propose a new vision-based approach for the automatic recognition of thermal events. This ROI-free approach, which relies on intelligent vision system concepts, is composed of two main tasks: hot spot detection and thermal event recognition. We present the results of our approach for the recognition of one critical thermal event and compare its performance with that of the previous system.

HgCdTe negative luminescence devices for cold shielding and other applications

Negative luminescence (NL) refers to the suppression of infrared blackbody emission, and hence an apparent temperature reduction, due to free carrier extraction from a reverse-biased p-n junction. A number of applications are envisioned for NL devices, including cold shielding of background-limited uncooled and cryogenic focal-plane arrays, dynamic nonuniformity correction for ir imaging, and ir scene simulation. High-performance NL devices have recently been demonstrated. For example, a HgCdTe/CdZnTe photodiode with 4.8-µm cutoff wavelength achieved an internal NL efficiency of 95% at room temperature. This means that the blackbody emission was suppressed by a factor of 20 and that the apparent temperature of the device surface decreased by 60 K. The corresponding reverse-bias saturation current density was 0.11 A/cm2. Even HgCdTe devices (λco=5.3 µm) grown on large-area silicon substrates with substantial lattice mismatch displayed 88% internal NL efficiency and saturation current densities no larger than 1.3 A/cm2. These results indicate a clear path toward a negative-luminescence device technology that is efficient, operates at low power, and is inexpensive.

Region-of-interest-based algorithm for automatic target detection in infrared images

We present a region-of-interest-based segmentation (ROI-S) algorithm and apply it for automatic target detection. The proposed algorithm requires no templates or a priori knowledge of the targets. An automatic ROI extraction approach based on localized texture and statistical features is used to locate targets in an IR scene without any prior knowledge of their type, exact size, and orientation. Two locally adaptive histogram-based segmentation techniques are applied to extract the target signature. The Bayes decision rule is applied for a bimodal histogram while entropic correlation is used for all other cases. Geometric and statistical features are automatically extracted for each suspected ROI. We suggest a unique variance-based metric for discriminating targets from clutter and for evaluating the probability of correct detection. The proposed system is successfully tested on several hundred single-frame IR images that contain multiple examples of military vehicles, with various sizes and brightness levels and in various background scenes and orientations. A high probability of correct detection (greater than 90%) with a low false alarm rate is achieved.

Bayesian inference of thermodynamic state incorporating Schwarz-Rissanen complexity for infrared target recognition

University of IllinoisCoordinated Science Laboratory1308 W. MainUrbana, Illinois 61801E-mail: lanterma@ifp.uiuc.eduAbstract. The recognition of targets in IR scenes is complicated by thewide variety of appearances associated with different thermodynamicstates. We represent variability in the thermal signatures of targets via anexpansion in terms of ‘‘eigentanks’’ derived from a principal componentanalysis performed over the target’s surface. Employing a Poisson sen-sor likelihood, or equivalently a likelihood based on Csiszar’sI-divergence (a natural discrepancy measure for nonnegative images),yields a coupled set of nonlinear equations which must be solved tocompute maximum a posterioriestimates of the thermodynamic expan-sion coefficients. We propose a weighted least-squares approximation tothe Poisson loglikelihood for which the MAP estimates are solutions oflinear equations. Bayesian model order estimation techniques are em-ployed to choose the number of expansion coefficients; this preventstarget models with numerous eigentanks in their representation fromhaving an unfair advantage over simple target models. The Bayesianintegral is approximated by Schwarz’s application of Laplace’s method ofintegration; this technique is closely related to Rissanen’s minimum de-scription length criteria. Our implementation of these techniques on Sili-con Graphics computers exploits the flexible nature of their renderingengines. The implementation is illustrated in estimating the orientation ofa tank and the optimum number of representative eigentanks for bothsimulated and real data.

Review of infrared scene projector technology-1993

The importance of testing IR imagers and missile seekers with realistic IR scenes warrants a review of the current technologies used in dynamic infrared scene projection. These technologies include resistive arrays, deformable mirror arrays, mirror membrane devices, liquid crystal light valves, laser writers, laser diode arrays, and CRTs. Other methods include frustrated total internal reflection, thermoelectric devices, galvanic cells, Bly cells, and vanadium dioxide. A description of each technology is presented along with a discussion of their relative benefits and disadvantages. The current state of each methodology is also summarized. Finally, the methods are compared and contrasted in terms of their performance parameters.

Thermal scene projectors using microemitters

A number of techniques are under development for creating dynamic IR scenes for testing IR imaging systems. Comparison of these techniques may be misleading if appropriate performance parameters are not used. One straightforward method is the thermal emission from microemitters fabricated in an array. The small mass leads to good response times if crosstalk between elements and to any substrate can be limited. Silicon micromachining can create good performance in arrays of this type because of the excellent thermal isolation of the elements

Directional effects on scene complexity in oblique thermal imagery and photographs of a deciduous forest

This paper presents an examination of thermal IR images and photographs of a mixed-specie deciduous forest in eastern Tennessee. Changes of scene complexity with changes of depression angle and azimuth relative to the sun are examined. Ground-based temperature measurements and canopy structure information are used to support the interpretation of view and solar geometry effects on thermal imagery. The green band of digitized oblique photographs from three azimuths are compared to thermal IR images obtained at similar view directions. Thermal IR scenes of the forest are most complex at small phase angles (angle between vectors to the sensor and to the sun) where photographic images were least complex. At these angles, sunlit subcanopy (nonfoliage) components are visible and much warmer than the leaves. At other directions, visible subcanopy materials are more shaded, and their temperatures are similar to leaf temperature. As view azimuth becomes more aligned with the sun, the transition to the more complex and warmer images is rapid. For visible light in this forest, scene complexity is primarily the result of crown illumination and shadowing. Viewing of shadows is minimized at small phase angles so the uniformly illuminated canopy appears simple.

Poles Apart?

In a recent essay for the German news magazine Der Spiegel, Rolph Dahrendorf, head of the London School of Economics, as something of an “outsider” to the British IR scene, stated: