Handheld directional reflectometer: an angular imaging device to measure BRDF and HDR in real time
Handheld directional reflectometer: an angular imaging device to measure BRDF and HDR in real time
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手持式定向反射仪：实时测量 BRDF 和 HDR 的角度成像设备
DOI：
10.1117/12.328461
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
B. C. Foos
中科院分区：
文献类型：
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作者：
Phillip R. Mattison;M. Dombrowski;James M. Lorenz;K. Davis;H. C. Mann;P. Johnson;B. C. Foos
许多应用需要对表面光散射进行定量测量，包括生产线的质量控制、油漆表面的检查、现场维修的检查等。用于测量表面散射的仪器通常分为两大类，即测量散射角分布的双向反射计和测量表面上方半球内的总散射的半球定向反射计。双向反射分布函数 (BRDF) 的测量可以最深入地了解光如何从表面散射。然而，BRDF 的测量通常是非常冗长的测量，通过移动源和探测器来绘制散射图。由于 BRDF 具有四个角度自由度，因此此类测量可能需要数小时至数天才能完成。尽管确实存在现场便携式双向反射计，但用于测量 BRDF 的仪器通常也是实验室设备。半球定向反射 (HDR) 是一种更容易进行的测量，但在超过 10 微米的波长下进行测量时必须注意使用正确的方法，因为积分球（通常用于进行此类测量）的能源效率非常低，并且在很长的波长下会失去其积分特性。确实存在一些现场便携式半球形定向反射仪，但通常仅在接近法线的角度测量 HDR。波音防务航天集团和表面光学公司根据空军研究实验室的合同，开发了一种新型手持式仪器，能够使用独特的专利角度成像技术测量 BRDF 和 HDR。半椭球面镜和附加透镜的组合将表面的角散射转换为二维空间分布，并由成像阵列记录。该配置通过超过 30,000 个角度解析点完整地映射了表面上方半球的散射，并将更新速率提高到每秒 60 次测量。然后，仪器根据测量的 BDR 计算 HDR。为了便于使用，该仪器还可以将 BRDF 和 HDR 与预设限制进行比较，生成 HDR 的通过/失败指示器以及 BRDF 的高可接受-低图像显示。光束入射高度可从法线入射（θ 等于 0 度）到掠射 5 度（θ 等于 85 度）变化，而散射测量结果为偏离法线近 90 度。这种能力对于任何需要了解倾斜视角下的表面外观的应用都极其重要。当前仪器的工作范围为 3 微米至 12 微米，并且可以扩展到可见光波段。
Many applications require quantitative measurements of surface light scattering, including quality control on production lines, inspection of painted surfaces, inspection of field repairs, etc. Instruments for measuring surface scattering typically fall into two main categories, namely bidirectional reflectometers, which measure the angular distribution of scattering, and hemispherical directional reflectometers, which measure the total scattering into the hemisphere above the surface. Measurement of the bi-directional reflectance distribution function (BRDF) gives the greatest insight into how light is scattered from a surface. Measurements of BRDF, however, are typically very lengthy measurements taken by moving a source and detector to map the scattering. Since BRDF has four angular degrees of freedom, such measurements can require hours to days to complete. Instruments for measuring BRDF are also typically laboratory devices, although a field- portable bi-directional reflectometer does exist. Hemispherical directional reflectance (HDR) is a much easier measurement to make, although care must be taken to use the proper methodology when measuring at wavelengths beyond 10 micrometer, since integrating spheres (typically used to make such measurements) are very energy inefficient and lose their integrating properties at very long wavelengths. A few field- portable hemispherical directional reflectometers do exist, but typically measure HDR only at near-normal angles. Boeing Defense and Space Group and Surface Optics Corporation, under a contract from the Air Force Research Laboratory, have developed a new hand-held instrument capable of measuring both BRDF and HDR using a unique, patented angular imaging technique. A combination of an hemi-ellipsoidal mirror and an additional lens translate the angular scatter from a surface into a two-dimensional spatial distribution, which is recorded by an imaging array. This configuration fully maps the scattering from a half-hemisphere above the surface with more than 30,000 angularly-resolved points and update rates to 60 measurements per second. The instrument then computes HDR from the measured BDR. For ease of use, the instrument can also compare both the BRDF and HDR to preset limits, generating a Pass/Fail indicator for HDR and a high-acceptable-low image display of BRDF. Beam incidence elevation is variable from normal incidence ((theta) equals 0 degrees) to 5 degrees off grazing ((theta) equals 85 degrees), while scattering is measured to nearly 90 degrees off normal. Such capability is extremely important for any application requiring knowledge of surface appearance at oblique viewing angles. The current instrument operates over the range of 3 micrometer to 12 micrometer, with extension into the visible band possible.