The melt temperature is calculated

The melt temperature is calculated to within ± 4 °C by using an emissivity correcting
pyrometer. The pyrometer uses a pulsed laser to calculate the reflectivity of the surface that it is
measuring. The emissivity of the surface can then be calculated using Kirchhoff’s law of thermal
radiation and then used to correct the temperature readings based upon the changing emissivity
of the melt as its temperature varies. [8] An array of K-type shrouded thermocouples and an
Omega thermocouple DAQ are used to measure the temperature at the bottom of the substrate at
six different points along its axis.