Non-penetrative thermal convection in a large-aspect-ratio container of water has been studied using stereoscopic Particle Image Velocimetry (PIV) to measure 3D velocity vectors in planar domains. The unique aspects of this work are the application of stereoscopic PIV in highly turbulent flow with significant small-scale energy, and the application of a liquid-filled test section which requires significant corrections for aberrations. Velocity data were obtained for three different cases of non- penetrative convection, corresponding to convective velocities, w*, of 3, 4, and 5 mm/s. For each case, a sequence of about 20 pairs of stereo-photographs were recorded in a vertical plane, with sufficient time separation between photographs to ensure statistical independence at least for the turbulent motions with time-scales on the order of z*/w*. The grid-spacing of the resulting velocity fields was adequate to resolve the smallest structures in the flow.