主动法测量比辐射率是通过对方向半球反射率的测量而间接获得的,由于在2n空间中测点有限,且主动光源存在对目标物的加温现象而使测量结果误差较大。被动法测量比辐射率存在两个问题;一是被测物的温度无法获得;二是很难从传感器中分离出环境辐射经目标物反射的部分。为避免直接测量目标温度和排除环境辐射的影响而提出过“箱式法”、“双温度法”等比辐射率测量方法,然而所有这些方法都无法测量比辐射率的方向特性。为了能较精确地量化环境辐射项,制作了一个直径为3m多的球体,在背景辐射的普适性计算公式基础上,利用双通道热辐射仪在两个温度下用自动观测装置测量了抛光铝板方向热辐射亮度值,最后计算得到铝板的方向比辐射率值。

The active measurement method of emissivity is done by measuring the directional half-sphere reflectance,and it has big errors because of the limited measured points in 2π space and the object heated by the radiative resource.The passive measurement method of emissivity has two problems; it is hard to directly get the temperature of object and difficult to separate the radiance of environment reflected by object from the sensor. In order to avoid measuring the temperature of object and eliminate the radiance of environment, the "box" and "two-temperature" methods have been put forward, but it is impossible to measure directional emissivity. For calculating the radiance of background, we built a boll with more than 3 meter diameter, and in the boll we measured the radiance of aluminum slab in different view angle under two different temperatures using the two-channel sensor attached on automatic frame, then we got directional emissivities of aluminum slab based on the common equation about radiance of background.