An experimental method is reported for the evaluation of the transmittance, in the wavelength range, of the hypersonic flow of the SCIROCCO Plasma Wind Tunnel. The experimental setup for the measurements consists of a thermocamera and a black body placed on opposite sides of the facility, with hypersonic plasma in the middle of them. The situation is representative of the conditions at which thermographic acquisitions are performed in SCIROCCO, when the medium between the target object and the sensor is the flowfield inside the test chamber. Moreover, in this way it has been possible to evaluate the transmittance in the wavelength range of interest of three different types of medium: environmental air, hypersonic freejet, and shock wave region around a body.