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为考核该方法是否具有良好工程适用性和较高的测量精度,通过辐射特性测量精度比对进行实验验证,实验选取对海作用距离试验中400 mm口径中波红外成像系统作为测试载体,其红外辐射测量系统参数设置如表1所示。另采用600 mm×600 mm的标准方形面源黑体作为真值目标,黑体架高固定在近海可移动的靶船上,黑体温度设置从60 ℃开始逐渐升温至130 ℃,每10 ℃设置为一个温度间隔,为减少外部环境影响,试验整体测量时间控制在1 h以内完成。
Parameter name Value Aperture/mm 400 Band/μm 3.7-4.8 Pixel number 640×512 Pixel size/μm 15 Bit depth/bit 14 Integration time/μs 1500/2500 Table 1. Parameter setting of infrared radiation measurement system
图5为实验中波红外实时拍摄目标截取图像,黑色方框内为传统图像二值化处理方法识别出的目标区域,圆形框内为瑞利分布法识别出的目标区域。并给出该基于瑞利分布方法处理该目标在X(Y)方向的灰度分布图,从图中可以看出两者很好的拟合在一起。
考虑目标成像清晰且便于分析与判断的原则,观测距离设置为3.5 km的高山上,经理论计算目标成像约为4×4,满足大于10倍的辐射源尺寸的要求,因此可以将此标准辐射源黑体看成点目标处理。图6为该黑体不同温度时刻呈现在MATLAB上的灰度变化,从图像上可以看出,选取出的点目标在1500 μs积分情况下的70 ℃、90 ℃、110 ℃和130 ℃成像能量分布均呈现出典型瑞利分布形式[13]。而且目标成像灰度值区间在4000~14000之间,满足中波红外成像系统最低灰度可探测值约1500,最高灰度可探测值约15000要求,且成像像元数来说满足点目标测量计算的要求。
为检验基于瑞利分布对弱小目标能量判断方法是否具备较好的测量精度,将应用传统图像二值化处理[14]得到的辐射强度与应用基于瑞利分布图像处理得到的辐射强度进行比对实验,在相同的外部环境条件下,采用同一的红外辐射特性测量设备,选取相同的积分时间和温度,以面源黑体辐射源作为测量真值,利用两种不同方法下辐射强度测量值与黑体标定真值之差作为测量偏差,即测量精度,得到数据结果如表2所示。
t/μs Temperature/℃ Blackbody radiation
intensity/×
10−2 W·sr−1Radiation intensity with
binaryzation/×
10−2 W·sr−1Error Radiation intensity with
Rayleigh distribution/×
10−2 W·sr−1Error 1500 60 3.0846 3.5106 13.81% 3.1572 2.35% 70 4.1615 4.5597 9.57% 4.1441 −0.41% 80 5.5209 5.9500 7.77% 5.5857 1.17% 90 7.2124 7.5829 5.14% 7.3901 2.46% 100 9.2898 9.7716 5.19% 9.3119 0.23% 110 11.8104 12.3958 4.96% 11.3885 −3.57% 120 14.8351 15.5974 5.14% 14.8336 −0.01% 130 19.1106 20.5432 4.42% 19.5578 0.70% 2500 60 3.0846 3.4156 10.73% 3.2901 6.66% 70 4.1615 4.4879 7.84% 4.2319 1.69% 80 5.5209 5.8564 6.08% 5.5331 0.22% 90 7.2124 7.5955 5.31% 7.0158 −2.72% 100 9.2898 9.8316 5.83% 9.3011 0.12% 110 11.8104 10.5275 −10.86% 11.9808 1.44% 120 14.8351 15.2391 2.72% 14.1766 −4.43% 130 18.4276 19.2415 4.42% 18.5578 0.70% Table 2. Comparison of measurement results of different calculation methods
通过对比和分析不难发现,应用基于瑞利分布方法的辐射强度测量偏差绝对值可控制在8%以下,而应用传统图像二值化处理方法得到的辐射强度值偏差绝对值高达20%以上;而且从图7也可以看出,应用基于瑞利分布的计算方法得到的测量数据离散程度更小,集中度更高[15]。因此在探测距离较远、大气情况复杂、目标弥散严重、整体图像对比度低等目标与背景边界区别不明显情况下,应用基于瑞利分布目标能量计算方法可有效提高特性测量精度。
Research on energy calculation method of weak and small targets based on Rayleigh distribution
doi: 10.3788/IRLA20220408
- Received Date: 2022-06-14
- Rev Recd Date: 2022-12-07
- Publish Date: 2023-02-25
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Key words:
- Rayleigh distribution /
- point target /
- measurement accuracy /
- infrared radiation characteristics measurement
Abstract: With the continuous progress of science and technology, military targets are developing towards miniaturization, ultra-high speed and low detectivity, so the detection and identification ability of targets is also put forward higher requirements. Based on the deep analysis of point target imaging process and on the basis of energy distribution, based on abnormal Rayleigh distribution of point target energy calculation method, the infrared radiation characteristics and has a better precision than the experimental verification, it is concluded that the measurement deviation of radiation intensity can be controlled under 8%, and measuring the degree of discrete numerical smaller, can effectively distinguish between the point target and background. It is proved that the calculation method has good engineering applicability, high measurement accuracy and wide application prospect.