High-resolution bathymetric data (ASCII format) of the head of Martínez Channel and of Steffen fjord (Chilean Patagonia, 48°S)

The bathymetry was mapped with an ELAC Seabeam 1050 multibeam system in austral winter 2016. A mounting frame holding two 50 kHz transducers at a 120-degree angle, was installed at the bow of the R/V Sur Austral (COPAS Sur-Austral, Chile). In order to correct for roll, pitch, and heave movements, an Octans Motion Sensor (IXSEA) was placed on the mounting pole above the transducers. CTD measurements were continuously recorded at the water surface (approximately 1 m depth) using a Valeport Modus CTD. To correct for sound velocity changes with depth, a total of 24 vertical CTD profiles were taken with an RBR Maestro, operated at a sampling rate of 6 Hz and vertical speed of 1 m/s. The multibeam data were processed with Caris HIPS and SIPS v9.1, including tide correction based on tide tables at Caleta Tortel (maximum tidal range of 1.9 m). The final bathymetric maps and grids were created using Fledermaus v7 and GMT. The data file is in ASCII XYZ format.