The REP 18 is centered on 2 main scenarios which will aggregate series of objectives. By doing this we’re able to focus resource use and maximize the benefit of having PT Navy vessels at our disposal while, at the same time, trying to reduce the inherent costs of those resources. The scenarios will take place on the areas represented on the map.
Impact of Tidal Variability on Coastal Stratification
This scenario centers on the collection of hydrographic data (CTD) using a LAUV (Xplore-2) during the course of 5-6 days along a specific transect in a region close to the navigation channel in the mouth of Sado estuary. The scenario days will be spread out along all the REP-Atlantic 17, and its focus is to have various samples of the same area over the course of a 10-15 day period in order to study the vertical structure and short-temporal variability of the region of influence of Sado estuary outflow during summer and the impact of warmer estuarine water in the coastal stratification. Moreover, all collected data should be used a posteriori to calibrate and validate numerical models implemented in the Sado estuary and adjacent coast. The possibility of the chlorophyll and turbidity sensors installation in the LAUV (Xplore-2) should be studied in a sense of convenience to maximize scientific opportunities, covering potential links between hydrographic and biological parameters.
The LAUV will perform the transect, present in Figure 1, over the course of 13 continuous hours. By doing so the data collected has the coverage of a full tidal period in the selected section of the ocean (about 12 hours and 25 minutes).
Additionally, in order to study the vertical structure of the velocity magnitude and direction in the region of influence of the Sado estuarine outflow, an Acoustic Doppler Current Profiler (ADCP) will be anchored along the planned transect. Again, this will allow to characterize in depth the temporal variations and vertical velocity structure, the surface and bottom currents changes within tidal cycles over the course of the mission and, afterwards, will also allow examining the accuracy of numerical models implemented in this region.
As an added feature there will also be deployed an ASV (Caravela) with an EchoSounder, a CTD and, if feasible, an ADCP covering the same transect, although not at the same time, with the purpose of studying small-scale differences of velocity profiles and evaluate sea surface temperature and salinity changes along the transect.
Moreover, a UAV (X2O-01) will be deployed from the PT Navy vessel in order to capture thermal imaging from the transect area during the LAUVs operation cycle. High-resolution data from X20-01 will constitute a detailed improving in the sea surface temperature observation during this scenario. Furthermore, it is possible other type of imaging payload will be on-board the UAV. This will be reliant on specific invited partners. Nevertheless, due to the endurance limit of the UAV, this vehicle’s operation will be limited to flights of 40min total with even less amount of “time-on-target”. Still since all data will be collected within known timeframes and will be georeferenced and timestamped it can then be correlated with the data collected from the LAUV.
Finally, if the LAUV deployments coincide with opportunistic passages from Sentinel satellites missions from ESA:
And other NASA EOS missions such as:
Then it will be possible to have an idea of the synoptic ocean conditions of the survey (i.e. upwelling/downwelling events) and/or to examine in detail structures observed in the transect that were generated offshore (i.e. internal waves) or in other remote locations.
On the generation of nonlinear internal waves in the Sado Estuary ROI
This scenario will take place south east from Portinho da Arrabida and will encompass multiple system deployment, seen on the map, to maximize quality data collection. It centers on unique observations of nonlinear internal solitary waves in the region of influence of the Sado Estuarine outflow using new and emergent oceanographic instrumentation.
Internal solitary waves (ISWs), generated by strong nonlinearity where internal waves can develop into sharp solitons wherein the thermocline dramatically shoals tens or hundreds of meters in only a few minutes, appear to be a key contributor because of turbulence they produce when they propagate and/or break (St. Laurent et al., 2011). These ISWs play an important role in transferring heat, energy, and momentum in the ocean and the turbulence they produce when they break is now recognized as a vital aspect of the ocean's meridional overturning circulation. Because numerical circulation models cannot simultaneously resolve climate and internal wave scales, IW breaking must be parameterized in these models. The magnitude and distribution of IW-driven mixing is then of critical importance to ocean models, and hence a major motivation for the study of oceanic internal waves.
In this scenario high-resolution observations will be performed to study the front vertical and surface structure, including measurements of velocity, salinity, water temperature, turbulence, turbidity and optical backscatter throughout the water column, using a synergetic network between LAUVs, Wavy’s, UAVs, and remote sensing platforms.
Moreover, utilizing the latest technology available installed onboard LAUVs (OMST), we intend to measure shear microstructure and coincident density structure from which we derive the dissipation rate of turbulent kinetic energy (ε) (Palmer et al., 2015). These measurements will be the first attempt to characterize the turbulence properties in the study region and one of the first turbulence direct observations taken from an internally recording microstructure instrument mounted to an autonomous platform, such a LAUV.
