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.