Techniques Improvement for Environmental Monitoring in Barrier-Island Systems on the Brazilian Equatorial Coast
Barrier-Island, Mophodynamics, Remote Sensing
The Brazilian Equatorial Coast comprises an extensive segment (≈ 5000 km) of a passive margin tectonic environment, in which the northernmost sector (Amapá to Maranhão) is wetter, presents high river discharge and is dominated by tidal forces (macrotidal). While in the southern sector (Maranhão to Rio Grande do Norte), the climate is more arid, river discharge is not significant and the modulation of the coastline is carried out by the joint action of tides (mesotidal) and wave energy. Despite the large extent, coastal studies are concentrated especially in the State of Rio Grande do Norte, many of which were financed by the oil industry attempting to deal with erosion problems. In this sector, the most studied morphological features are the barrier-island systems, which comprise the islands themselves, tidal channels, inlets, plains and associated deltas, as well the mangroves forests. For a long time, it was believed that barrier-island systems were exclusive to this coastal segment, however, today it is clear that they are relatively common features, capable of appearing even in macrotidal conditions. However, most barrier-island systems remain poorly studied, either from the point of view of their characterization or the lack of comparison with other similar features around the world. The study of these environments is not always a simple task, often access to field information is hindered by the natural conditions of the area and/or operational cost. In this sense, many works resort using remote sensing and digital image processing to overcome such limitations. Therefore, this work aims to study of barrier-island systems along the Brazilian Equatorial Coast in order to gather and reassess existing conceptualizations in the literature, establish parallels with their analogues around the world, and propose the improvement of techniques based on sensing remote for the environmental monitoring of its constituents (e.g. islands and mangroves). Therefore, the following hypotheses were proposed: i) the classic models of genesis and evolution of the barrier-islands do not fully describe the cases observed on the Brazilian Equatorial Coast; ii) satellite-extracted beach profile monitoring method can guarantee a faithful estimate of the sediment bypass in ephemeral features; iii) coastal aquifers in the semi-arid region contribute to maintaining the health of mangrove ecosystems in hypersaline estuaries. The methods employed aim to extract planimetric data and band indices of medium and high-resolution optical images (Landsat 8, Sentinel 2, Planet Tasking), as well as radar images (Sentinel 1). These data will be integrated with field information, such as geodetic surveys of beach profiles, tide gauge stations, vibracore logs and piezometers. Preliminary results reveal the necessity to analyze the morphodynamics of tidal-dominated barrier-island systems. In addition, it was observed that the models of genesis and evolution of barrier-island systems need to be adapted to the Brazilian reality. This work also proposes a new technique to quantify the volume of sediments remobilized between the shoreface, foreshore and backshore in an ephemeral barrier-island. The effectiveness of this method must be proven during the development of this research.