Processed Autonomous Underwater Vehicle (AUV) multibeam bathymetry and backscatter data collected during RRS Discovery cruise DY200 in Haig Fras and Whittard Canyon, Atlantic Ocean, 2025

Multibeam Echosounder (MBES) bathymetry and backscatter data were acquired in the Haig Fras and Whittard Canyon Marine Conservation Zones (MCZs), Atlantic Ocean, using the Autonomous Underwater Vehicle (AUV) Autosub5-mounted Norbit WBMS-bathy MBES during RRS Discovery Cruise DY200 between 23/09/2025 and 12/10/2025. The AUV was used to map in high resolution: the Greater Haig Fras MCZ (mission AS5M124), and the Whittard Canyon MCZ (Dangeard Interfluve, missions AS5M127 and AS5M131). Mission AS5M127 left a gap in coverage due to the AUV prematurely surfacing; mission AS5M131 was subsequently conducted to fill this gap, completing the full survey of the target area. Bathymetric data were processed using Quality Positioning Services (QPS) Qimera 2.7.6, while backscatter data were subsequently processed using QPS FMGT 7.11.2. Tidal corrections were derived separately for the Greater Haig Fras and Whittard Canyon sites using the Polpred online application (NOC Innovations), based on the GTM_16HC tidal model, and applied to the respective datasets. CTD-derived sound velocity profiles (SVPs) were then used to further refine the acoustic corrections, and the TU Delft Sound Speed Inversion Tool was additionally applied to correct residual refraction errors. Semi-automatic and manual cleaning procedures were carried out to remove erroneous soundings, particularly along the outer swath edges. Mission AS5M131 was spatially adjusted relative to AS5M127 through the identification of common seafloor features, to ensure consistent alignment between the two surveys. For each site, bathymetric grids were generated at 1 m resolution in WGS84 UTM Zone 29N projection, using the CUBE (Combined Uncertainty and Bathymetry Estimator) algorithm. Processed .gsf files were then exported to QPS FMGT to produce backscatter mosaics at 0.20 m resolution. Both backscatter and bathymetry data are supplied in .xyz format. Additionally, bathymetry is supplied in ESRI ASCII Raster format, and backscatter as GeoTIFF files. These datasets were collected by scientists from the National Oceanography Centre, Southampton, UK, as part of two funded projects: the NERC National Capability programme AtlantiS (Atlantic Climate and Environmental Strategic Science), which supports long-term repeat surveys of deep-water benthic habitats at UK Marine Conservation Zones, and the Horizon Europe-funded project REDRESS (Restoration of Deep-sea habitats to Rebuild European Seas), which aims to demonstrate the feasibility and value of deep-sea ecosystem restoration.