The development of most energy conversion systems is focused on increased efficiency and decreased pollutant emissions. However, the diesel engine combustion process suffers from the systematic trade-off between soot-oxidation and NOR-formation in the vicinity of the diffusion-flame surface. Since this process is influenced by the local flame surface temperatures, it is of great importance to investigate and understand the factors influencing the surface temperature distribution itself. For this reason, a new combination of measurement techniques called "stereoscopic 3-color high-speed ratio-pyrometry" has been developed at RWTH Aachen University. This system provides a double-redundant quantification of the temperature, topology and emissivity distributions of an optically opaque diesel-flame with a temporal and spatial resolution of 10,000 images/s and 16 Pixels/mm(2) in this set-up. Still, the system only consists of a high-speed camera, a stereoscopic double-row adapter and three optical filters. The first part of this paper includes a brief description of the theoretical fundamentals, experimental hardware, required calibration procedures and post processing algorithms to provide a general understanding about the developed measurement technique. Based on this, the second part of this paper is used to present the results of the first experimental investigations conducted on a continuously scavenged high-pressure chamber test-bench. These results indicate a general dependency between the local surface temperature and optical density, caused by several parallel processes. (c) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.