Abstract
Up until the last ten years, remote sensing data and especially high-resolution satellite data and airphotos were mainly used in shallow water mapping. The evolution and low cost of unmanned aerial vehicles (UAVs) provides a new tool for coastal area monitoring. This paper presents the synergistic use of a small commercial UAV and an unmanned surface vehicle (USV) for beachrock mapping in Syros Island, Greece. RGB images collected with a quadcopter were processed using Structure from Motion (SFM) photogrammetry in order to create digital surface models (DSMs) and orthophotos of the coastline. A beachrock lying in shallow waters was detected and mapped using the UAV derived products. At the same time, a USV equipped with a compact side scan sonar (SSS) and bathymetric sonar system, provided the shape of the beachrock by mosaicking the backscatter strength of the SSS. In order to evaluate the results of the UAV and USV data derivatives, the beachrock perimeter and its depth were also mapped using a differential global navigation satellite system (GNSS) receiver. During the fieldwork, samples from the beachrock were collected and analyzed in the laboratory. The mineralogical composition of the bulk samples was determined by powder X-ray diffraction (XRD). Further petrographic study was also performed by petrographic polarizing microscope, macroscope, and scanning electron microscopy (SEM). Beachrock samples are classified as fine to medium grain sandstones and conglomerates. The mineral compositions of their grains and lithoclasts reflect the bedrocks of Syros Island (mainly metamorphic rocks) while a micritic high-Mg calcite constitutes the cement of these rocks.
Highlights
Beachrock is an intertidal beach deposit with a carbonate cement
The importance of beachrocks can be summarized in the following main topics: their impacts on coastal evolution [12], their role as sea-level indicators [6,7,8,9], the information they contain regarding the coastal processes of cementation and palaeo-environmental evolution [13,14,15], and the control that they exert on beach hydrodynamics [16,17]
The results show that the mol % of MgCO3 in cement phase of samples of area 1 ranges from 4% to 16%, characterizing this as high magnesium calcite (HMC)
Summary
Beachrock is an intertidal beach deposit with a carbonate cement. There are several processes involved in beachrock formation, including direct precipitation from meteoric waters, mixing of marine and meteoric waters, degassing of CO2 , evaporation, and microbial carbonate mineral precipitation [1,2,3,4,5]. As far as we know, for the first time, remote sensing data from an unmanned aerial vehicle (UAV) and an unmanned surface vehicle (USV) are combined with data derived from petrographic and mineralogical analyses in order to conduct a deep investigation of a beachrock formation in Lotos Gulf, Syros Island, Cyclades, Aegean Sea, Greece. The proposed integrated methodology seeks to answer two key issues that have been raised by the scientific community concerning the beachrocks; the accurate mapping and their consequent use as sea level change indicators and the processes of cementation which are indicative of the mechanism Minerals of their formation. This unit is mainly composed of marbles, schists, metabasites, and paragneisses [47], Massif
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