This online page at The Pyrometer Instrument Company website, discusses the emissivity correction techniques employed in their products, the very narrow waveband devices called the Pyrolaser® (Shown here), the Pyrofiber® & the Optitherm® III Emissivity Technology.
(Notes: 1. The article speaks about “emissivity” but the spectral emissivity is implied due to the fact that these devices operate in very narrow wavebands at 865nm, 905nm or 1550nm, according to the model.
2. The article also provides a calculation and describes the radiant power of the laser as “energy”.)
Here’s an edited quote from the page:
“The emissivity is measured by firing a pulsed laser of monitored output energy to the target and measuring the reflected laser energy. Assuming that no energy is transmitted through the target (opaque material) the impinging energy must either be absorbed or reflected.
“The unknown absorbed energy can be calculated from the two measured quantities outgoing energy and reflected energy.
“Since absorptivity and emissivity are equal…the target emissivity (e) is known as soon as the absorptivity is known.
The temperature is measured by collecting the radiance in a narrow band (10-50nm) at the same wavelength (865nm, 905nm or 1550nm depending on the specific instrument) where emissivity is measured with the laser.”