Repetitive bathymetric surveys in the Lütschine delta (Lake Brienz, Switzerland)

Description

This dataset includes Multibeam Echo Sounder Digital Bathymetric Models (DBMs or DEMS) and their associated Digital Uncertainty Models (DUMs) from the proximal Lütschine Delta of Lake Brienz, Switzerland. Surveys were performed in 2018 and 2023. By subtracting the DBMs within a GIS software (QGIS or ArcGIS) , a DBM of Difference (DoD) reveals the changes in the lakefloor over a five-year period. These surfaces contain a few areas with missing data, therefore an interpolated surface for 2018 is also included for mapping purposes.

Steps to reproduce

The two Digital Bathymetric Models (DBMs) were acquired in 2018 and 2023 to assess bathymetric changes occuring in the Lütschine Delta (Lake Brienz, Switzerland). The 2018 survey covers the whole Lake Brienz except areas shallower than 5 meters water depth. Additionnally, a more recent DBM was obtained in the proximal Lütschine Delta in 2023. Both hydrographic surveys utilised a Kongsberg EM2040 multi-beam echosounder (Kongsberg Maritime, Horten, Norway) operating at a frequency of 300 kHz with a maximum angular coverage of 148° (74° to each side). Survey lines were spaced to ensure an overlap. Vessel motion and orientation was determined with a Seatex MRU5+motion sensor (Kongsberg Seatex, Trondheim, Norway), heading with a Trimble SPS361 heading sensor (Trimble Navigation Limited Sunnyvale, CA, USA). A Leica GX1230 GNSS receiver (Leica Geosystems, Heerbrugg, Switzerland) in combination with the swipos-GIS/GEO real-time positioning service (Swiss Federal Office of Topography, Wabern, Switzerland) was used for positioning. Before the survey, the Sound Speed Profile (SSP) of the water column was measured using a sound-velocity sensor (Vale-port Limited, Totnes, UK). Sound Speed Surface (SSS) was permanently monitored during the survey using a Valeport MiniSVS sensor (Valeport Limited, Totnes, UK). The software CARIS HIPS/SIPS 10.4.37 (Caris, Fredericton, Canada) was used to process the datasets. Gridded georeferenced surfaces were generated using CUBE (Combined Uncertainty and Bathymetric Estimator) algorithm. CUBE creates a depth model (the DBM) and simultaneously provides an estimate for depth uncertainty . This surface containing an absolute value of uncertainty for each cell (pixel-wise uncertainty) is referred here to as Digital Uncertainty Model (DUM) Two estimates of uncertainties were done, one theoretical another more conservative. Georeferenced surfaces were computed as a structured grid with a cell size of 2x2 m in the Swiss coordinate system (ESPG:25065 – CH1903+LV95) and exported as tif format.

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