這是老外寫的：

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.

頭暈了吧，簡單來說，我們可以這樣來測試物體的熱輻射率：

• 找一塊已知輻射率的物體，比如黑色絕緣膠布，其輻射率0.97,把它貼到待測物體上面，同時(shí)用熱電偶貼到膠布的位置測試溫度，然后用紅外熱像儀去拍攝，如果熱電偶的溫度和膠布的溫度不同，則需要調(diào)整熱像儀里面的輻射率設(shè)置，直到相同為止。這是校正儀器步驟。
• 校正完成后，用沒有貼膠布位置的溫度與貼膠布位置的溫度相除，得出一個(gè)比值，這就是被測物體的輻射率了。（這個(gè)是錯(cuò)誤的）
• 把膠布去除掉，溫度沒變，這時(shí)候儀器力的溫度肯定會(huì)變化，和有膠布時(shí)不同，再調(diào)整儀器里的輻射率，知道溫度恢復(fù)到和原來有膠布的時(shí)候一致，此時(shí)的輻射率值就是待測物體的實(shí)際輻射率。