  The paper introduces a multi-scale processing method for quantitative study
and visualization of convective heat transfer using diffractive optical element
based background-oriented schlieren technique. The method relies on robust
estimation of phase encoded in the fringe pattern using windowed Fourier
transform and subsequent multi-scale characterization of the obtained phase
using continuous wavelet transform. As the phase is directly mapped to the
refractive index fluctuations caused by the temperature gradients, the
multi-scale inspection provides interesting insights about the underlying heat
flow phenomenon. The performance of the proposed method is demonstrated for
quantitative flow visualization.
