We investigated a supersonic flowfield with transverse injection of air or helium by stereoscopic particle image velocimetry and calculated single-time two-point spatial correlations of velocity fluctuations. For both injection gases, the bow shock wave formed by the injection and its reflection from the upper wall could be seen in the mean velocity distribution. In the velocity fluctuation intensity distribution, we observed vibrating counter-rotating vortex pair and the Reynolds stress was formed along the track of the maximum mean velocity gradient. Correlations showed the scale structure of turbulence and the shapes of the correlation region changed with the selected velocity component. Differences were observed between the results obtained for the two injectant species.