这是老外写的：

Emissivity is the scientific term for a material’s ability to emit thermal radiation. Each material has different emissivity, and it can be quite a task to determine the appropriate emissivity for a subject. A material’s emissivity can range from a theoretical 0.00 (completely not-emitting) to an equally-theoretical 1.00 (completely emitting); the emissivity often varies with temperature.
An example of a substance with low emissivity would be silver, with an emissivity coefficient of .02.
An example of a substance with high emissivity would be asphalt, with an emissivity coefficient of .98.
A Black Body is a theoretical object which will radiate infrared radiation at its contact temperature. If a thermocouple on a black body radiator reads 50 °C, the radiation the black body will give up will also be 50 °C. Therefore a true black body will have an emissivity of 1.
Since there is no such thing as a perfect black body, the infrared radiation of normal objects will appear to be less than the contact temperature. The rate (percentage) of emission of infrared radiation will thus be a fraction of the true contact temperature. This fraction is called emissivity.
Some objects have different emissivities in long wave as compared to mid wave emissions. Emissivities may also change as a function of temperature in some materials.
To make a temperature measurement of an object, we refer to preset emissivity tables to choose the emissivity value of the object, which is then entered into the camera. The camera’s algorithm will correct the temperature by using the emissivity to calculate a temperature that more closely matches the actual contact temperature of the object.
During quantitative thermal imaging surveys, we try to test the emissivity of the object in question. This would be more accurate than attempting to determine the emissivity of the object via a table. The usual method of testing the emissivity is to place a material of known high emissivity in contact with the surface of the object. The material of known emissivity can be as complex as industrial emissivity spray which is produced specifically for this purpose, or it can be as simple as standard black insulation tape, emissivity 0.97. A temperature reading can then be taken of the object with the emissivity level on the imager set to the value of the test material. This will give an accurate value of the temperature of the object. The temperature can then be read on a part of the object not covered with the test material. If the temperature reading is different, the emissivity level on the imager can be adjusted until the object reads the same temperature. This then gives us a much more accurate emissivity reading. There are times, however, when an emissivity test is not possible due to dangerous or inaccessible conditions (i.e looking at plant chimneys or shielded buss bar units). In these situations we thus rely on tables.

头晕了吧，简单来说，我们可以这样来测试物体的热辐射率：

找一块已知辐射率的物体，比如黑色绝缘胶布，其辐射率0.97,把它贴到待测物体上面，同时用热电偶贴到胶布的位置测试温度，然后用红外热像仪去拍摄，如果热电偶的温度和胶布的温度不同，则需要调整热像仪里面的辐射率设置，直到相同为止。这是校正仪器步骤。
~~校正完成后，用没有贴胶布位置的温度与贴胶布位置的温度相除，得出一个比值，这就是被测物体的辐射率了。~~（这个是错误的）
把胶布去除掉，温度没变，这时候仪器力的温度肯定会变化，和有胶布时不同，再调整仪器里的辐射率，知道温度恢复到和原来有胶布的时候一致，此时的辐射率值就是待测物体的实际辐射率。