Habitat mapping and morphological characterization of extremely shallow environments through spectral and textural analysis of high resolution bathymetric and backscatter data

Among the coastal systems, transitional environments, like lagoons, deltas and estuaries, are often extremely shallow (of the order of 1 m deep or less) and morphologically complex. These environments often undergo strong natural and human-induced actions that need constant monitoring. The changes of these environments can be assessed using acoustic bathymetric surveys. Bathymetric surveys with multibeam echosounders (MBES) and interferometric systems allow to collect at the same time bathymetric and backscatter data that can be employed for geomorphologic studies and habitat mapping. These instruments have become a very important tool to study the evolution trends of the highly dynamical coastal areas. However, transitional environments represent a challenge for acoustic bathymetric surveys. To assess the potentiality and the limits of acoustic surveys in extremely shallow environments, we carried out two surveys in the Lagoon of Venice, Italy, with an interferometric sonar and a MBES. As a case study we focused on a natural channel in the northern part of the lagoon (Figure 1) combining the data from the different surveys. In particular we carried out a two-dimensional (2D) spectral and textural analysis of the high resolution bathymetric and backscatter data collected. As a result of the 2D spectral analysis on the elevation data, we were able to identify and parameterize the geometrical characteristics of the main morphological features of the channel, like dunes, scours, crests and troughs and sedimentation areas and to extract the channel bottom roughness. We then performed an unsupervised classification of the backscatter data. As a result, we were able to identify different backscatter areas where several grab samples were collected for ground truthing. With the help of this sampling we calibrated a textural analysis and obtained a classification of the different kinds of substrate. Within this multidisciplinary approach, we could map the main morphological and sedimentological features of the seabed trying to relate them to the habitats of an extremely shallow water dynamical environment.