Multibeam data were collected during R/V Polarstern cruise ANT-XXIII/1. Data recording was executed for calibration of sonar system Atlas Hydrosweep DS2 and for studies to minimize the acoustic impact of the Atlas Hydrosweep and Parasound echosounders on the marine environment in the Bay of Biscay. Data are unprocessed and may contain outliers and blunders. For that reasons the data should not be used for grid calculations and charting projects but need to be processed furthermore. One file contains a measurement period not exceeding eight hours. The dataset consists of 16 files in ATLAS SURF format which are compressed with GZIP to size of 182 MB. SURF data files can be processed using the software packages CARIS HIPS/SIPS or with the open source software package MB-System (http://www.ldeo.columbia.edu/res/pi/MB-System/). The source code for an application programming interface (API) to read and write SURF data is released by the Hydrosweep manufacturer Atlas Hydrographic, Bremen, and published under the GNU GPL. Contact mailto:infobathy@awi.de for data access.