This data set contains raw data synchronously collected by various CTD instrument during the DAUNE experiment. The goal of this experiment was to reach a common understanding of how measurement uncertainty can be derived initially focusing on temperature data.After developing a strategy for measuring and implementing high-quality data, the collected data was analysed for the purpose of estimating measurement uncertainties. The resulting procedures were defined in a step-by-step process, taking into account the different perspectives of the authors as well as the special conditions for environmental measurements, which are collected while the observed volume/area is undergoing a constant change.In this context, the data available here were used to provide a universally applicable method for the systematic evaluation of in-situ measurement data with regard to the quantification of the uncertainty of the measurement results.