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首先根据飞机红外辐射特性建立飞机排气系统和机体的红外辐射计算模型,然后考虑辐射传输路径上的大气衰减及探测器接收到的背景辐射,求解探测器视场内的目标和背景辐射亮度;最后将亮度值进行灰度量化,生成飞机的红外灰度图像,并根据所得图像求解飞机的红外辐射强度。
得到蒙皮温度场后,将蒙皮看作灰体,应用普朗克定律和基尔霍夫定律可得蒙皮自身辐射的红外辐射亮度,其计算公式为:
$$L_{\rm s}=\dfrac{\varepsilon}{\pi} \int_{\lambda_1}^{\lambda_2} \dfrac{c_1}{\lambda^5\left[{\rm e}^{c_2 /(\lambda T)}-1\right]}{\rm{ d}} \lambda $$ (1) 式中:ε为蒙皮发射率,与蒙皮材料和波长有关,对于飞机蒙皮材料通常可取ε=0.8;c1与c2为辐射常数。
蒙皮面元的红外辐射亮度等于自身辐射亮度与反射太阳辐射亮度之和,即
$$ L=L_{\rm s}+L_{\rm sun} $$ (2) 根据飞机的红外计算模型,分析计算结果得到飞机红外辐射的光谱特性、方位特性,以及发动机状态、飞行速度、高度等因素对飞机红外辐射的影响[6]。
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面源红外干扰弹投放后在载机附近迅速扩散开来形成红外干扰云团,其与被保护载机的红外图像相似,或改变载机的红外图像特征,欺骗红外成像制导导弹,继而诱使红外成像制导导弹偏离被保护的载机[7]。
面源红外干扰弹作为一种自燃金属箔片,其辐射模型受到材料的物理性能和化学反应、空气气流的热交换以及干扰弹扩散规律等决定。由于燃烧反应物质有限,干扰弹红外辐射随时间必然是一个先增大后减小的过程,红外辐射强度随时间的变化规律如图2所示。
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多点源红外干扰弹发射后形成多个分散的点源红外干扰弹,连续投放后形成多个点状发热体。采用多发齐射或多方位齐射时,可迅速在一定空域形成红外高辐射区,并在导引头瞬时视场内形成持续的多个干扰源,将目标信号淹没,导引头就必须处理多组脉冲信号,降低了导引头检测目标的概率,红外导引头即使启动了抗干扰措施,但因探测器的噪声几何级数增大,而难以提取有效的制导信号,从而起到保护载机的作用[8-11]。
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点面复合红外干扰弹是点源与面源红外干扰弹的物理组合,通过在单发干扰弹内同时装填点源/面源干扰载荷,发射后在一定空间区域形成辐射强度大于载机巡航态、辐射面积大于载机、能有效抑制红外制导导弹的多种抗干扰检测措施的面源红外诱饵辐射云团和红外辐射源。面源红外辐射云团和红外辐射源与载机同处于来袭导弹导引头的视场内,点红外辐射源与目标红外辐射逐渐融合,严重破坏目标红外辐射特征,通过强红外辐射干扰源对红外制导导弹实施压制、转移式干扰;面源红外辐射云团能够使导引头的跟踪中心逐渐偏向红外辐射源,并能够掩盖和歪曲红外成像探测系统所要观察的目标征候及信号特征,混淆目标的大小、位置和数量,从而有效降低导引头的目标识别与跟踪性能。
动力光谱红外干扰弹的运动特征为:发射后以发射时的初始绝对速度基本达到匀速平飞,装药燃尽后红外干扰弹减速下降。其速度、高度的变化如图3所示。图中,
$ V_{0} $ 和$ H_{0} $ 为发射时的初始绝对速度和高度;$ t_{m} $ 为动力光谱红外干扰弹的有效作用时间。 -
红外定向干扰属于光电有源干扰,通过红外激光光源和跟踪瞄准转台向导引头发射激光光束,持续对红外制导导弹进行主动干扰压制,在验证试验中,利用中波红外激光对数千米外中波导引头进行照射,可在导引头视场内形成一定面积的干扰耀斑,实现有效干扰[12-13],如图4所示。
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由于飞机、导弹在远距离时,其成像不能充满跟瞄系统的瞬时视场,可作为红外点源处理,跟瞄系统作用距离公式为:
$$ R=\left[\frac{\pi \cdot \delta \cdot \tau_{\rm a} \cdot \tau_{0} \cdot J \cdot D^{*} \cdot D_{0}^{2}}{4 \cdot \sqrt{A_{\rm d}} /\left(2 t_{\text {int }}\right) \cdot S N R}\right]^{1 / 2} $$ (3) 式中:
$ \delta $ 为信号峰值因子;$\tau_{\rm {a }}$ 为大气透过率,采用MOTRAN软件计算;$ \tau_{0} $ 为系统光学效率;D*为探测率;D0为跟瞄系统光学口径;Ad为探测器光敏元面积;$ t_{\text {int }} $ 为探测器积分时间;SNR为探测所需信噪比,取5;J为目标红外辐射强度。 -
大气相干长度为:
$$ r_{0}=\frac{C \lambda^{6 / 5}}{\left(C_{n}^{2} L\right)^{3 / 5}} $$ (4) 式中:
$ C $ 为常数,对于平面波,取0.185;${C}_{n}^{2}$ 为折射率结构特征参数,一般来说,近地面湍流强度可粗略分为三类:强湍流$ C_{n}^{2}=10^{-12} \mathrm{~m}^{+200} $ ,中湍流$ C_{n}^{2}=10^{-14} \mathrm{~m}^{+200} $ ,弱湍流$ C_{n}^{2}=10^{-16} \;{\rm{m}}^{-2 / 2} $ ;$ \lambda $ 为激光波长;$ L $ 为目标距离。在传输过程中受大气湍流影响,光斑发散角将放大,湍流放大系数为:
$$ A^{\prime}=\sqrt{\left(1+\left(\frac{D}{r_{0}}\right)^{2}\right.} $$ (5) 式中:
$ D $ 为激光发射装置的有效发射口径。激光束经敌方目标光学系统会聚后,照射到敌方探测器靶面上的光斑直径为:
$$ d^{t}=f \theta_{0} A^{t}+2.44 \lambda F $$ (6) 式中:
$ f $ 敌方光学焦距,$ f=D \times F $ ;$ \theta_{0} $ 为激光发射装置出射口的激光发散角;$ F $ 为敌方光学系统的F数。最终激光入射到敌方探测器上的激光功率密度为:
$$ E=P_{0} \tau_{\rm a} \tau_{0} \frac{A_{0} \cos \sigma}{\pi\left(L \theta_{0} A^{\prime} / 2\right)^{2} \times \pi\left(d^{\prime} / 2\right)^{2}} $$ (7) 式中:
$ P_{0} $ 为激光发射功率;$ \tau_{0} $ 为敌方光学系统的光学透过率;$ A_{0} $ 为敌方光学系统通光面积;$ \sigma $ 为攻击角。假设敌方光学目标的干扰阈值为
$E_{\text {th }}$ ,则当$E > E_{\rm th}$ 时,可成功干扰敌方目标。由上述各公式可迭代计算出红外定向干扰系统对目标的最大干扰距离$ L $ 。
Simulation of airborne terminal infrared countermeasure operational effectiveness
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摘要: 为研究飞机末端红外对抗作战效能,通过建立红外对抗仿真系统,分别对飞机红外特性、诱饵干扰特性、激光定向干扰特性进行建模仿真,通过红外特征实时解算的方法建立红外对抗场景,结合不同作战环境、干扰场景的飞机末端防御,进行红外图像渲染和模型解算,为红外干扰效能评估提供实时的红外对抗场景。结合典型的作战态势和飞机机动方式,仿真分析了导引头视场内的目标与诱饵动态红外场景,进行飞机末端防御的不同干扰手段干扰效能评估和干扰使用策略研究。仿真结果表明,飞机红外对抗仿真系统能有效地对末端红外对抗作战效能和干扰策略想定进行研究。Abstract: In order to study the operational effectiveness of aircraft terminal infrared countermeasure, the infrared countermeasure simulation system is established to model and simulate the aircraft infrared characteristics, decoy jamming characteristics and laser directional jamming characteristics respectively. The infrared countermeasure scene is established by the method of real-time calculation of infrared characteristics to combine the aircraft terminal defense of different operational environments and jamming scenes. Infrared image rendering and model solving are carried out to provide real-time infrared countermeasure scene for infrared jamming effectiveness evaluation. Combined with the typical combat situation and aircraft maneuver mode, the dynamic infrared scene of target and decoy in the seeker field of view is simulated and analyzed, and the jamming effectiveness evaluation and jamming use strategy research of different jamming means for aircraft terminal defense can be carried out. The simulation results show that the aircraft infrared countermeasure simulation system can effectively study the operational effectiveness and jamming strategy formulate of the terminal infrared countermeasure.
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