This paper presents a spaceborne SAR mission concept in Ku-band for the measurement of the two-dimensional ocean surface current. The measurement concept is based on dual-beam along-track interferometry, which requires two highly squinted antennas each looking simultaneously in fore and aft direction. A single side-looking geometry and a ScanSAR imaging mode is chosen to complete the observational concept in order to achieve the requirements on revisit-time and coverage. The applied hybrid polarization is intended to increase the information level about different ocean scattering mechanisms. Furthermore a methodology of instrument requirement derivation is briefly discussed, ensuring the ocean current measurement accuracy requirements. Finally the instrument concept, including digital beamforming, and the SAR performance are presented.