A methodology for the estimation of the soot volume fraction in a three-dimensional laminar diffusion flame is presented. All experiments are conducted in microgravity and have as objective producing quantitative data that can serve to estimate radiative heat transfer in flames representative of fires in spacecraft. The competitive nature of formation and oxidation of soot and its direct coupling with the streamlines (source of oxygen) require for these measurements to be conducted within the exact configuration. Thus three-dimensional measurements are needed. Ethylene is injected through a square porous burner and the oxidizer flows parallel to its surface. The methodology uses CH* chemiluminescence measurements to correct for three-dimensional effects affecting light attenuation measurements. Corrected local soot concentrations are thus obtained. All experiments are conducted during parabolic flights and the parameters varied are fuel and oxidizer flow rates.