In this work, a measurement technique based on a single-beam coherent gradient sensing (CGS) interferometer is used to obtain line-of-sight projections of a 3-D temperature field in a convective fluid medium. Due to its inherent insensitivity to vibrations, simple and cost effective optical layout, and, most importantly, the absence of a separate reference beam, CGS is an attractive choice for measurements in convective fluids. In the present study, line-of-sight interferometric projections of a differentially heated water medium in a cylindrical cavity are presented for a cavity aspect ratio (diameter/height) of 3.9. The 3-D temperature field is then obtained using the line-of-sight interferometric projections with a 3-D tomographic reconstruction algorithm. The temperature field obtained shows the absence of a radial-symmetric pattern at a Rayleigh number of 1.6×10⁵, which is in agreement with observations from the literature.