New systems and methods to access the temperature of the melt pool in welding processes have been developed to study phenomena, monitor behaviours, and even be used in closed-loop control strategies. Concerning arc welding processes, the arc radiation might impose a challenge to measure the temperature. However, heat input is the key point for welding quality. This work aims to evaluate the feasibility and detect potentialities of accessing the thermal field from the rear weld pool in the GTAW process by using in-house developed equipment. The original system was conceptualized based on a previous bichromatic method. Experiments were carried out with and without the wire feed addition, and welding parameters were varied to explore its impacts on the temperature measurement. A strategy to select the regions of interest (ROIs) within the weld pool was created, and the mean temperature was calculated and correlated to the weld bead features. This strategy was able to overcome the challenges imposed by the electrode/nozzle reflection and the arc radiation during the welding. The rear weld pool thermal field was shown to be an important source of data to provide hints of the weld bead features. The mean temperature can indicate geometrical changes in the weld bead. Furthermore, the technique has the potential to be used as a promising real-time process monitoring tool.