Abstract
The human impact on the ecosystem has been particularly evident in the last century; it transforms the Earth’s surface on an unprecedented scale and brings about irreversible changes. One example is an oceanographic phenomenon known as a tombolo, i.e., a narrow belt connecting the mainland with an island lying near the shore formed as a result of sand and gravel being deposited by sea currents. The phenomenon contributes to an increase in the biogenic substance content in the littoral zone, which leads to increased cyanobacteria blooming in the summer period. Moreover, the debris accumulation in the littoral zone results in the mud formation, which makes the beach landscape less attractive. One of the main features of the tombolo phenomenon is its variability of shape, which includes the form of both the shore and the seabed adjacent to it. Therefore, to describe its size and spatio-temporal variability, it is necessary to apply methods for geodetic (the land) and hydrographic (the sea) measurements that can be carried out in different ways. The aim of the paper is to present the methodology for carrying out measurements of the tombolo oceanographic phenomenon using Unmanned Aerial Vehicles (UAV) and Unmanned Surface Vehicles (USV) on the example of a waterbody adjacent to the Sopot pier. It also presents the results of surveys carried out in November 2019 within this area. The study demonstrated that the integration of two measuring devices whose development began in the second decade of the 20th century, i.e., UAVs and USVs, enables accurate (even up to several centimeters) and reliable determination of the scale and variability of the phenomena occurring in the littoral zone.
Highlights
Until recently, the equipment and measurement methods used in hydrography were not accurate enough and characterized by insufficient coverage of the seabed with measurements
Current survey techniques used by hydrographers include, among others, the tachymetric method [1,3], the geodetic method that an operator conducting the measurement on the submerged beach at predefined depth with the use of a Global Navigation Satellite System (GNSS) receiver working in real time [4,5], as well as determining coastal water depths based on analysis of high-resolution images taken by Landsat and Sentinel satellites [6,7,8]
Unmanned surface vehicles are used in marine and inland hydrography [11,12], especially in waterbodies, on which shallows occur [13]
Summary
The equipment and measurement methods used in hydrography were not accurate enough and characterized by insufficient coverage of the seabed with measurements. They are used for tasks related to supporting the navigation process [14], in underwater photogrammetry [15], or in geological works [16] When it comes to unmanned aerial vehicles, they are used to: determine the terrain relief adjacent to the sea shore [17,18], monitoring coastline changes [19], in research on geomorphological processes occurring in the littoral zone [20,21], or in bathymetric surveys in shallow waters [22,23]. Experimental research was carried out in a waterbody adjacent to a pier in Sopot (Poland), where a tombolo had been formed as a result of the construction of a yacht marina near the shore [24,25,26] To this end, two unmanned vehicles were used: an UAV for photogrammetric measurements of the littoral zone land area, and an USV for hydrographic surveys of the shallow waterbody. The multi-sensory integration of data obtained during the study determined the scale and variability of the tombolo phenomenon occurring near the Sopot pier and its effects on the aquatic ecosystem
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