The Hydrographic Doppler Sonar System (HDSS), is now 20 years old and is getting upgraded when R/V Revelle undergoes her midlife refit this summer and fall. HDSS is a state-of-the-art system for measuring ocean currents. We are substantially upgrading and improving the old system, with enhancements including greater power and real-time beam forming that corrects for the roll and pitch of the ship, improving precision by keeping the beams much more constant orientation.