Single beam echo-sounding dataset and digital elevation model of the southeastern part of the Baltic Sea (Russian sector)

We present the bathymetric dataset of a single beam sounding. Surveys were conducted in 25 expeditions of the Atlantic branch of Shirshov Institute of Oceanology RAS in the Russian EEZ area of the southeastern part of the Baltic Sea in the period from 2004 to 2018. Acoustic data were acquired by echo sounders Simrad EA-400SP and Furuno FS-700. The raw sounding data were filtered and corrected by sound velocity values. The dataset is presented as spreadsheets (*.xslx) and GIS point-class shapes (*.shp). The digital elevation model (DEM) of 1: 500 000 scale has been constructed for the entire Russian EEZ on base of the original array of sounding profiles and an open sources bathymetry [1]. DEM is presented by XYZ-grid (*.txt) and GeoTIFF raster (*.tif).


Data
The presented dataset includes: -The spreadsheets (*.xlsx) of processed data of single-beam sounding obtained by Simrad EA400SP (Fig. 1) and Furuno FS-700 ( The structure of the spreadsheets (*.xlsx) and the attribute tables of the shapefiles (*.shp) is presented in Table 1.

Study area and expeditions
The study area is the Russian EEZ and territorial waters in the southeastern part of the Baltic Sea (Fig. 3).
The bottom relief of the Baltic Sea is characterized by series of depressions and sills between them, narrow troughs and shallow banks. The Gdansk basin is the most part of the study area. There is the Gdansk-Gotland Sill on the north of the study area. It separates the Gdansk Deep from the Gotland Deep (Fig. 3) Type of data Spreadsheets (*.xslx), GIS feature classes (*.shp), Geotiff raster (*.tif), XYZ-grid (*.txt) How data was acquired Continuous profiles of the bathymetric data acquired in marine surveys with using by the single-beam echo-sounders -Simrad EA 400 SP (Kongsberg Maritime, Norway) and Furuno FS-700 (Furuno, Japan).

Data format
Calibrated and processed spreadsheets, GIS layers, interpolated raster and XYZ-grid Experimental factors The raw XYZ data of echo sounding (*.txt) were converted into MS Excel spreadsheets (*.xlsx). Data preprocessing included filtering and sorting. The spreadsheets were converted in the point shapefiles with depth marks. We digitized isobaths from Ref. [1] for the areas of insufficient data. The dataset also includes coastline zero marks. The bathymetric raster surface was calculated by linear interpolation.  Fig. 4. The soundings were acquired by narrowbeam high-frequency echo-sounder Simrad EA400SP (Kongsberg, Norway) (Fig. 1) and the shipinstalled echo-sounder Furuno FS-700 (Fig. 2).
The Simrad EA400SP is hydrographic two-frequency echo-sounder operated at 38 and 200 kHz frequency channels. As a rule, we used the frequency of 200 kHz because it gives more exact depth then lower frequencies. We used the frequency of 38 kHz as on dense sediments and with the absence of the technical possibility of using the frequency of 200 kHz (Fig. 4). The accuracy of depth measurements is 1 cm at 200 kHz frequency and 5 cm at 38 kHz. The echo-sounder Furuno FS-700 was operated at 50 and 200 kHz frequency channels (Fig. 4). It was used in the absence of the Simrad EA400SP on a board. The accuracy of the Furuno FS-700 is 0.1 m or 2% of the depth.
The measured depths and coordinates from DGPS were recorded in the echo-sounders console in the digital format. The depths were measured from the echo-sounder transducer. The echograms and depth values were recorded in *.raw format which was converted into XYZ tables (*.txt) for further processing. We measured the temperature and salinity profiles for the sound velocity parameters (SVP) corrections in each expedition.

Processing of the sounding data
The processing of raw data was performed in the MS Excel software. The raw data were converted from the XYZ data files using macros written in the Visual Basic for Applications (VBA). The data were filtered for outliers and spurious depth values. The SVP and position of the transducer below water level were used for the depths correction. The processed data were compounded in spreadsheets (*.xlsx) as shown in Table 1. These data were thinned through 150e200 m using a VBA macros and saved in another spreadsheets (*.xlsx). The spreadsheets of thinned data were converted into ArcGIS in point-class shapefiles (*.shp) of WGS1984 UTM Zone 34 N projection for further use and construction of the DEM.

The DEM construction
The dataset for DEM construction includes: -the echo sounding data presented in this article; -the digitized isobaths of the bathymetric map of the Central Baltic Sea [1]; -the digitized isobaths of the coastal nautical charts.
The shapefiles of the sounding data were plotted in ArcGIS. The areas with insufficient data were determined (Fig. 5). Isobaths from Ref. [1] and nautical charts were digitized and net of regular depths were calculated for these areas. These depth values were converted to the point shapefiles. We also added coastline zero marks as point shapefile to the general array for correct interpolation. All shapefiles of general data array were combined into ArcGIS dataset. From that one we created a terrain   dataset by using the ArcGIS 3D Analyst module (Terrain To Raster). In this instrument, natural neighbor interpolation is applied through the triangulated terrain surface. The DEM has a spatial resolution of 50 m and a horizontal scale of 1:500 000 (Fig. 3). The obtained DEM of the bottom relief is presented as the GeoTIFF raster (*.tif), ASCII XYZ-grid (*.txt) and the ESRI ASCII Grid (*.txt).