Techniques applicable to visualization and scalar measurements in large-scale hydrogen fires are highly desired, but lacking. In this research, planar thermal images of a buoyancy-driven unsteady laminar hydrogen/air flame and line images of a thin filament stretched across this flame were obtained using an infrared (IR) camera at a sampling frequency of 348Hz. A pulsing frequency of 11Hz was measured. Transient line measurements of temperature (T) and water vapor mole fraction (XH2O) have been achieved using inverse radiation calculations. Instantaneous XH2O and T distributions during a flame–vortex interaction cycle were obtained with temporal and spatial resolutions of 3ms and 1.7mm, respectively. The instantaneous distributions of XH2O and T were effected by preferential diffusion and the altered velocity field of the flame. Vortices caused more scalar fluctuations outside the flame surface than inside. The present XH2O and T measurements are consistent with detailed chemistry calculations of the flame and laser diagnostic measurements of similar flames. With some modifications, the thermal imaging based technique can be extended to large-scale hydrogen fire applications.