Three-dimensional structure of coral reef boulders transported by stormy waves using the very high resolution WorldView-2 satellite

Coral reef boulders have been showed to reliably characterize the amount of wave energy related to cyclone, storm or tsunami events. The wave height and current velocity have been successfully explained by the variability in the boulder individual (morphology) and population (distribution) spatial patterns. Even if a single boulder may include a substantial amount of information, it may be highly challenging to characterize it given the access difficulty at the local and regional scales. Moreover, a boulder population is meaningful to robustly and continuously depict the energetic event that drove the sediment transportation. Recently the very high resolution satellite remote sensing has been demonstrated to help classify and measure the horizontal patterns (A- and B-axes) of the boulders at the submeter scale. Here we focus on the vertical dimension (C-axis) of the boulders. Based on boulder fieldwork measurements of the three axes and geographic locations, we constrain various spectral parameters of the remotely sensed datasets (WorldView-2) to retrieve the three axes of the boulders, reaching a very satisfactory agreements (R-2) of 0.95, 0.88 and 0.75, respectively. The innovative C extraction combined with the A and B information will allow geomorphologists to rapidly and extensively collect boulder data so that the underlying energy can be computed in a more expanded and accurate way, at the population scale.