A method and apparatus for casting a molten metallic material in ingot form are provided wherein the molten metallic material is transported to the ingot mold and an upper surface temperature and temperature distribution of the molten metal pool in the casting mold are measured by an imaging radiometer which is disposed external to an inert gas filled chamber enclosing the ingot mold, and is disposed to view the ingot pool surface through a sight port. At least one plasma arc torch is employed to direct an arc at the ingot pool surface, the intensity of which is selectively modulated and the impingement of the arc is simultaneously selectively positioned in order to maintain a desired preselected mold pool surface temperature and temperature distribution thereby yielding a preselected metallurgical structure in the solidified ingot. The imaging radiometer may provide a video signal as an output, and may be connected to a video analyzer and video monitor which are used to provide an image of the surface temperature and temperature distribution, enabling an operator to control the plasma arc torch in performing the ingot casting method.