The line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Both electronic and photographic methods are employed for specklegram recording. The subsequent specklegram treatment uses the Young's fringes method as well as the cross-correlation analysis of small interrogation regions of the recordings. For laminar flows, the local and global Nusslet numbers were determined via measuring local surface temperature gradients for convective heat transfer from vertical isothermal plates of different configurations. The results were compared with Ostrach's theory and with data obtained by Mach-Zehnder interferometer. The 3D temperature fields were reconstructed for axisymmetric convective flows around a suddenly heated vertical wire using single projection measurement and Radon inversion. For turbulent flows, the temperature field microstructure was analyzed with the help of the correlation and structural functions. The 2D correlation function (CF) of the deflection angles of probing light was transformed into 3D CF of temperature field using Erbeck-Merzkirch integral transformation. Both macro- and microscales of turbulence were evaluated using this CD. The variation of the turbulence microscales due to interaction of turbulence with a shock wave was studied and analyzed.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.