The intensive development of remote sensing in the marine environment provides excellent bathymetric and substrate mapping opportunities on the southern Bulgarian Black Sea coast. The Bay of Chernomorets is a perfect opportunity to combine data from single-beam sonar, multi-beam sounding and drone imaging for the purpose of seabedforms and substrate mapping. This paper presents the second stages activity of the Project �Multidisciplinary study of Burgas Bay � MidBay. (Composition of a detailed digital model of the bottom relief with analysis of modern geomorphological conditions and archaeological forecasting modelling)� with a scientific goal of creating a substrate map and identification of seabed forms. The studied bay is strongly anthropogenically modified by the port in its southern part. In recent years, systematic studies of the landform changes have shown that the seabedforms, the beach and the shallowest part up to 2 meters in depth have changed. This is the main reason for choosing a solution that allows the 3D reconstruction of a coastal sector of Chernomorets. One of the purposes of the publication is to review the research through echo sounders and unmanned aerial systems along the Bulgarian Black Sea coast and analyse the methodology, equipment, and results obtained. The main task is to use good practices and successful methodology to combine echo-sounding and UAV surveys to derive a modern digital model of the terrain and raster data for the Bay of Chernomorets. Additionally, the process follows the good practices of using UAV and Sonar raster mosaic to detect borders between lithological varieties. The article aims to map seabed substrates in Folk 5 Classes and evaluate the accuracy of UAV-based DSMs, high-resolution orthomosaics and singlebeam echo sounding, which are fundamental for studying the most dynamic coastal landforms along the Bulgarian Black Sea coast.

Recently, the echosounder systems in the Bulgarian Black Sea shelf have become a standard method of seabed exploration. The paper presents the present-day field activity of bathymetric research, which revised available hydrographic data for the seabed. The study aims to combine and update archival bathymetric data from contemporary multibeam echo-sounding scanning and archive single-beam data. This work presents activity in the second stage of Project �Multidisciplinary study of Burgas Bay � MidBay. (Composition of a detailed digital model of the bottom relief with analysis of modern geomorphological conditions and archaeological forecasting modelling)� with a primary scientific goal to create an overall bathymetric model of the Burgas and Pomorie bays. The studied bay is strongly anthropogenically modified by the port in its southern part. The reconstruction of seafloor topography will allow the detection of substrate varieties and the identification of contemporary geomorphological bedforms and processes. A historical review of hydrographic research and geo base database was created for the seabed of the Bulgarian coastal zone in support of this study with different-year bathymetric surveys. The used data consolidate sonar mosaics, single beam, multibeam bathymetric data and raster satellite images, processed in PDS 2000, SonarWiz, and GIS environment. The coverage and density of the bathymetric data allowed the generation of a seabed digital bathymetric model with a horizontal resolution of 11 m. In addition, a bathymetric map with an interval of 0.5 m was created with high accuracy. Such a high-resolution model is an important advance in the highresolution mapping of the Bulgarian Black Sea coastal zone.

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