An apparatus and process for a temperature measuring pyrometer probe that measures gas temperatures above the melting point of conventional thermocouple material. The apparatus is used to calculate radiation heat losses and compensate for pneumatic cooling from the thermocouple junction of the pyrometer probe. The pyrometer probe has an inner hollow body which defines an inner chamber. The inner hollow body has an open end and the inner chamber is in communication with ambient gas surrounding the pyrometer probe. The inner hollow body is mounted within an outer hollow body and such mounting defines cooling channels. The cooling channels accommodate fluid flow which cools the inner hollow body. The ambient gas is directed into a converging-diverging nozzle, mounted within the inner hollow body, toward a thermocouple junction. The converging-diverging nozzle has a wall suction channel through which a boundary layer of the ambient gas is drawn away from the thermocouple junction. The thermocouple junction is mounted within a throat section of the converging-diverging nozzle. The pyrometer probe is intermittently cooled with gas by pulsing reverse cooling gas flow through the pyrometer probe. A computing system is used to continuously acquire temperature signals from the thermocouple and alternate the cooling gas flow and the ambient gas flow through the inner chamber of the pyrometer probe based on the temperature response. The computing system calculates radiation heat transfer losses, pneumatic cooling of the pyrometer probe, and instantaneous gas temperatures.