Limits of a comparative evaluation of the performance of a conventional X-band marine radar (MR) sigma S6 WaMoS® II used for surface current measurements are dicussed. Main focus of the paper is to address challenges when comparing current measurements from different measuring devices for evaluation purpose. Although the current measurement principles of MRs and acoustic Doppler current profilers (ADCPs) are disparate, they are often used to validate the quality of MR current measurements. In fact, differences in MR and ADCP derived currents can have a variety of physical reasons and do not necessarily indicate measurement errors. One possible cause of deviation is the comparison of dissimilar quantities. While MR radars yield spatially (∼km2) and temporally averaged (minutes) surface currents, ADCPs deliver subsurface and compared to MRs small scale measurements referring to different coherent intervals in time and space. The difference in spatial and temporal sampling strategies, in combination with the inhomogeneity of ocean current fields with horizontal and vertical shears caused e.g. by local eddies, fronts or internal waves [1], yield to a misalignment, and hence to a decorrelation of the MR and ADCP data sets. Nevertheless, several studies have reported good agreement between surface current MR data and subsurface current ADCP data. Typically, MR surface current speeds are reported stronger than those measured by ADCPs. With increasing depth from the surface, a clockwise (Northern Hemisphere) rotation between MR surface current and ADCP subsurface currents was also reported [2]. Therefore, a direct comparision between MR and ADCP current measurements per se cannot reveal the quality and accuracy of the measurements nor the general performance of measurment device. Only in cases where vertical and horizontal homogeneity can be assumed, a direct comparison is scientfically meaningful. This paper presents a comparison and discussion of sigma S6 WaMoS® II MR derived surface currents and subsurface (20-50m water depth) ADCP current observerations, acquired onboard the German polar research vessel Polarstern during the 2015-2016 expedition ANT-XXXI. To stress the different measurement conditions, specific periods covering different current characteristics are presented and discussed. During periods selected to represent vertically homogenous conditions, surface and subsurface currents can be assumend to be similar enough to be compared directly. Under those conditions, the sigma S6 WaMoS® II and ADCP measurements show excellent agreement with a correlation of r > 0.9, verifing the general precision of sigma S6 WaMoS® II surface current measurements. Under conditions with significant vertical current shear the current observation by sigma S6 WaMoS® II and ADCP show different results. This was the case when Polarstern was crossing the equatorial current system. The equatorial under current (EUC) which is located in about 100m water depth was observed by the ADCP and not by sigma S6 WaMoS® II observations. However, this deviation does not reflect erroneous or inaccurate current measurements. As the EUC does not extent to the surface it can not be observed there. In fact, this investigation further demonstrates the potential of MR surface current measurements to fill in missing surface current information from ADCPs, as ADCPs are not used to measure surface currents of the ocean [2].