Acoustic Doppler Current Profiler Measurements Research Articles

Estimation of Suspended Sediment Concentration by Using Mobile ADCP Instrument

The measurement of suspended sediment concentration (SSC) by using Acoustic Doppler Current Profiler (ADCP) instrument still not widely used in Indonesia. The application of this technology uses sound wave by four direction transducers placed in the vessel, and this ADCP measured the intensity of backscatter from sediment particles. This study is equipped with RD Instruments WorkHorse Mariner 307.2 kHz ADCP, and the water sample collected from Lembeh Strait, North Sulawesi by using van Dorn bottle sampler. Beyond the experimental purpose of this installation, the interest in having wide area data at different tidal condition is that it provides the possibility of determining the effect of tidal to the SSC. The losses of sound signal were corrected to get more accurate results. Simple linear regression analysis performed to obtain the estimates of the SSC. Estimation of SSC of ADCP measurement was then compared with SSC on water analysis in the laboratory, and the result showed that insignificantly different by statistical analysis. From this research, it showed that the concentration of suspended sediment ranged between 60-73 mg L−1 on location near the Port of Bitung, and 50-62 mg L−1 at a location away from the port. The result also observed that the highest concentration is in the region below the water column, and tidal condition was affected the condition of SSC. Based on all analysis, the mobile ADCP can provide a suitable measurement of suspended sediment concentration.

A Deep Eastern Boundary Current in the Chile Basin

AbstractHydrographic data and tracers from several ship‐based sections show the location and structure of a deep eastern boundary current in the Chile Basin. The current is centered above the Peru‐Chile Trench at 2,500–3,400 m and transports up to 6 Sv of low‐potential vorticity, high‐silicate water south toward Drake Passage. Deep current velocities from direct Lowered Acoustic Doppler Current Profiler measurements are up to about 15 cm/s southward. The hydrographic data, as well as potential vorticity and silicate distributions, show that the current is comprised to a large extent of flow from the west moving along the southern flank of the Sala y Gomez Ridge and Nazca Ridge, and to a lesser extent from a flow along the eastern boundary entering directly from the Panama Basin. At the southern edge of the Chile Trench, the current weakens and partly turns offshore to cross the Chile Ridge through a complex region of passages. Above the southern flank of the Chile Rise the flow joins a broader eastward flow; together, these waters return to the eastern boundary before entering Drake Passage.

Intraseasonal-to-Interannual Variability of the Upper-Layer Zonal Currents in the Tropical Northwest Pacific Ocean

The upper-layer circulation in the Tropical Northwest Pacific Ocean (TNWP) is characterized by the alternating zonal currents, such as North Equatorial Current (NEC) and Subtropical Countercurrent (STCC). The variabilities of the upper-layer zonal currents in the TNWP, which were obtained directly from 75 kHz acoustic Doppler current profiler (ADCP) measurements and indirectly from geostrophic calculations, were investigated on intraseasonal to interannual timescales from 2006 to 2014. Surface geostrophic current derived from sea surface height anomaly (SSHA) approximated well to the in-situ measurements with ADCP that was slightly better than the absolute geostrophic current obtained from AVISO. The interannual signals related to the El Nino-Southern Oscillation (ENSO) were quite apparent, especially near the boundary (about 17.5°N–19°N) between NEC and STCC. We found that the eastward-flowing southern STCC develops during the decaying phase of ENSO and weakens during La Nina. Strong easterlies during strong La Nina (e.g., 2010 La Nina event) seem to influence NEC to expand further north to the southern STCC region and this coincides with the meridional migration of the Sverdrup streamfunction. The southern STCC region is profoundly influenced by the mesoscale/sub-mesoscale eddy activities, which can intensify the eastward flow of STCC and ultimately contribute to the intraseasonal signal. We found that this intraseasonal signal weakened when La Nina happened in 2010, which is presumably associated with the northward expansion of NEC. Possible factors related to the discrepancies between surface geostrophic current and sub-surface ADCP data are discussed.

Structure of the Deep Spillway in the Western Part of the Romanche Fracture Zone

AbstractStructure of the deep spillway was studied on the basis of conductivity‐temperature‐depth, lowered acoustic Doppler current profiler, and mooring measurements in 2011–2014 in the Romanche fracture zone (22°27′–22°32′W). The spillway exists quasi‐permanently in the regime of hydraulic control overflow and consists of two flows in the layer θ < 1.20 °C (deeper than 4,150 m). The first flow enters the fracture from the south through a gap in the Southern Wall. The second flow is directed to the east along the narrow valley of the fracture. The sill depths of these passages are 4,570 and 4,430 m, respectively. The depths over the surrounding ridges are shallower than 4,100 m. Both flows descend to the local depression of the fracture with 5,000‐m depth. Bottom potential temperatures over both sills were 0.51 °C, and the measured velocities were 20–40 cm/s. When the flows descend down the slope, they accelerate in supercritical regime. Maximal measured velocities were up to 65 cm/s. Analysis of the 189‐day time series of velocities on the mooring deployed in the flow descending from the gap showed a very high level of fluctuation energy: 10 times greater than the energy of the barotropic tide at this point. The only energy source of these fluctuations is the available potential energy of the deep thermocline in the West Atlantic transforming to the kinetic energy of the deep spillway. The total transport of the bottom water below θ = 1.2 °C based on the lowered acoustic Doppler current profiler measurements is estimated at 0.29–0.35 Sv, which agrees with the predicted values.

Characteristics of coastal currents based on High Frequency radar and ADCP observations in the Strait of Georgia

A good understanding of the water body movement in Strait of Georgia is of great importance and significance for a variety of economic and environmental applications. Circulation of surface currents in this region is influenced by a variety of factors such as tide, wind and river discharge. Hourly maps of surface currents are obtained through combining the radial currents from more than two stations. In order to explore performance of High Frequency (HF) CODAR radar system, currents observed by HF radars were compared with ADCP (Acoustic Doppler Current Profile) measurements. Results indicated that surface current data from HF radars generally had similar trend as the ADCP data.

Annual Sediment Transport Dynamics in the Narayani Basin, Central Nepal: Assessing the Impacts of Erosion Processes in the Annual Sediment Budget

AbstractIdentifying the roles of erosional processes in the denudation of mountain ranges requires a better understanding of erosional sensitivity to climatic, topographic, or lithologic controls. We analyzed erosion in the Narayani River basin (draining central Nepal and presenting contrasted lithologic and geochemical signatures in its outcropping rocks and a wide variety of erosional processes and climatic conditions) to assess the relative contributions of erosion processes to the annual sediment export. By combining acoustic Doppler current profiler measurements with depth profiles and daily surface samplings of the suspended load, we propose a simplified model to precisely calculate sediment fluxes at the basin outlet. We estimate an equivalent erosion rate of mm/year for the year 2010, similar to the average value of mm/year estimated from 15 years of records and long‐term (~ky) denudation rates of 1.7 mm/year derived from cosmogenic nuclides. The stability of erosion is attributed to efficient buffering behavior and spatial integration in the drainage system. Strong relations between rainfall events and the sediment export suggest that the system is mainly supply limited. Combining physical calculation of sediment fluxes with grain size analyses and geochemical tracers (hydroxyl isotopic compositions, carbonate contents, and total organic carbon content), we estimate that glacial and soil erosion do not contribute more than 10% and a few percentage, respectively, to the total budget and are only detectable during premonsoon and early monsoon periods. During the monsoon, erosion by landslides and mass wasting events overwhelms the sediment budget, confirming the dominant role of these erosional processes in active mountain chains.

Spatial Uncertainty in Depth Averaged Velocity Determined from Stationary, Transect, and Longitudinal ADCP Measurements

This study builds upon established methods for using acoustic Doppler current profilers (ADCPs) to measure velocities to include another measurement technique—longitudinal measurements—which are increasingly being used in open channel flow studies. Longitudinal measurements are collected in paths that parallel the streamwise direction as opposed to transect measurements, which are collected perpendicular to the flow direction. This study analyzed ADCP data that were collected concurrently using stationary, transect, and longitudinal collection methods in order to determine which method can be used to most effectively develop interpolated velocity maps. Data from the Pecatonica River in Freeport, Illinois, and the St. Joseph River in Berrien Springs, Michigan, were used as case studies for comparing measurement techniques. To compare interpolated velocities calculated using the longitudinal data collection technique with a traditional transect data collection scheme, the variables of data density and data collection effort were systematically altered to investigate both methods. Data collection effort time was utilized to provide equivalent velocity comparison between the ADCP data collection techniques. Plots that compared interpolated transect and longitudinal velocities to transect and stationary data illustrated that the longitudinal interpolated velocities match the known data and mimic the cross section velocity trend better than the interpolated transect depth averaged velocities. The longitudinal measurement technique was substantially better at describing the depth averaged velocity variation for the river reaches investigated.

Long-Term Mean Circulation of the Baltic Sea as Represented by Various Ocean Circulation Models

The skill of the state-of-the-art ocean circulation models GETM (General Estuarine Transport Model), RCO (Rossby Centre Ocean model), and MOM (Modular Ocean Model) to represent hydrographic conditions and the mean circulation of the Baltic Sea is investigated. The study contains an assessment of vertical temperature and salinity profiles as well as various statistical time series analyses of temperature and salinity for different depths at specific representative monitoring stations. Simulation results for 1970-1999 are compared to observations from the Baltic Environmental Database (BED). Further, we analyze current velocities and volume transports both in the horizontal plane and through three transects in the Baltic Sea. Simulated current velocities are validated against ten years of Acoustic Doppler Current Profiler (ADCP) measurements in the Arkona Basin and five years of mooring observations in the Gotland Basin. Furthermore, the atmospheric forcing datasets, which drive the models, are evaluated using wind measurements from 28 automatic stations along the Swedish coast. We found that the seasonal cycle, variability, and vertical profiles of temperature and salinity are simulated close to observations by RCO with an assimilation setup. All models reproduce temperature well near the sea surface. Salinity simulations are of lower quality from GETM in the northern Baltic Sea and from MOM at various stations. Simulated current velocities lie mainly within the standard deviation of the measurements at the two monitoring stations. However, sea surface currents and transports in the ocean interior are significantly larger in GETM than in the other models. Although simulated hydrographic profiles agree predominantly well with observations, the mean circulation differs considerably between the models highlighting the need for additional long-term current measurements to assess the mean circulation in ocean models. With the help of reanalysis data ocean state estimates of regions and time periods without observations are improved. However, due to the lack of current measurements only the baroclinic velocities of the reanalyses are reliable. A substantial part of the differences in barotropic velocities between the three ocean models and reanalysis data is explained by differences in wind velocities of the atmospheric forcing datasets.

Airborne Remote Sensing of Surface Velocities in a Tidal River

The global optimal solution (GOS) has proven to be very accurate for deriving water surface velocities from contemporaneous image pairs, but previous studies have used shore-based radars or satellite measurements with resolutions on the order of a kilometer or tens of meters to establish this. In contrast, the objective of this paper is to derive a GOS velocity field from infrared (IR) (3–5 $\mu \text{m}$ ) images having a 1-m pixel size. Because IR images can frequently exhibit a low signal-to-noise ratio, a newly developed GOS technique with a local similarity metric is used to retrieve velocities from such low-contrast data sets. To demonstrate the utility of this new method, we use airborne data collected in the tidal Potomac River over 11 days and spatially varying flood, ebb, and slack conditions. The resulting GOS-derived velocity estimates are compared against acoustic Doppler current profiler (ADCP) measurements taken simultaneously with the airborne collections. Velocity magnitudes and directions are found to have GOS versus ADCP correlations of 0.93 and 0.99, respectively. This high correlation suggests that the GOS technique may be applicable to a variety of lower contrast imagery that can now be collected by a low-altitude remotely controlled aircraft.

PARTICLE SIZE CHARACTERISTICS OF RIVERBED SEDIMENTS TRANSPORTED BY TIDAL BORE ‘BONO’ IN KAMPAR ESTUARY, RIAU-INDONESIA

The presence of tidal bore in the Kampar River (locally known as ‘bono’) may influence sedimentation in the Kampar River and its estuary. Understanding sedimentation mechanisms (e.g., erosion, deposition) is important to communities along the Kampar River, which can be studied by analyzing characteristics of grain size distribution. Here, we study riverbed sediment samples collected from 17 stations using an Ekman grab sampler, accompanied by bathymetry and acoustic Doppler current profiler (ADCP) measurements. Grain size data show that the sediments are coarser upstream and gradually finer downstream. Silty sands are predominant in the upstream section of the river, sands in its river body and sandy silts in the downstream. The results indicate the influence of undular bores on grain size characteristics. We also found that the propagation of bono and Kampar River’s funnelshaped morphology cause intense scouring events of riverbed sediments. Sortation values that range between 0.332.14 suggest unstable currents that result in randomly deposited sediments. The sediment mass transfer per area is positively towards downstream at the low tidal condition. However, after the passage of the bores, the sediment mass transfer area becomes negatively towards upstream.

Intrusions of Kuroshio and Shelf Waters on Northern Slope of South China Sea in Summer 2015

The northern slope region of the South China Sea (SCS) is a biological hot spot characterized by high primary productivity and biomasses transported by cross-shelf currents, which support the spawning and growth of commercially and ecologically important fish species. To understand the physical and biogeochemical processes that promote the high primary production of this region, we conducted a cruise from June 10 and July 2, 2015. In this study, we used fuzzy cluster analysis and optimum multiparameter analysis methods to analyze the hydrographic data collected during the cruise to determine the compositions of the upper 55-m water masses on the SCS northern slope and thereby elucidate the cross-slope transport of shelf water (SHW) and the intrusions of Kuroshio water (KW). We also analyzed the geostrophic currents derived from acoustic Doppler current profiler measurements and satellite data. The results reveal the surface waters on the northern slope of the SCS to be primarily composed of waters originating from South China Sea water (SCSW), KW, and SHW. The SCSW dominated a majority of the study region at percentages ranging between 60% and 100%. We found a strong cross-slope current with speeds greater than 50 cm s−1 to have carried SHW into and through the surveyed slope area, and KW to have intruded onto the slope via mesoscale eddies, thereby dominating the southwestern section of the study area.

Deflection of natural oil droplets through the water column in deep-water environments: The case of the Lower Congo Basin

Numerous recurrent seep sites were identified in the deep-water environment of the Lower Congo Basin from the analysis of an extensive dataset of satellite-based synthetic-aperture radar images. The integration of current data was used to link natural oil slicks with active seep-related seafloor features. Acoustic Doppler current profiler measurements across the water column provided an efficient means to evaluate the horizontal deflection of oil droplets rising through the water column. Eulerian propagation model based on a range of potential ascension velocities helped to approximate the path for rising oil plume through the water column using two complementary methods. The first method consisted in simulating the reversed trajectory of oil droplets between sea-surface oil slick locations observed during current measurements and seep-related seafloor features while considering a range of ascension velocities. The second method compared the spatial spreading of natural oil slicks from 21 years of satellite monitoring observations for water depths ranging from 1200 to 2700 m against the modeled deflections during the current measurement period. The mapped oil slick origins are restricted to a 2.5 km radius circle from associated seep-related seafloor features. The two methods converge towards a range of ascension velocities for oil droplets through the water column, estimated between 3 and 8 cm s−1. The low deflection values validate that the sub-vertical projection of the average surface area of oil slicks at the sea surface can be used to identify the origin of expelled hydrocarbon from the seafloor, which expresses as specific seafloor disturbances (i.e. pockmarks or mounds) known to expel fluids.

Advanced 3D Mapping of Hydrodynamic Parameters for the Analysis of Complex Flow Motions in a Submerged Bedrock Canyon of the Tocantins River, Brazil

Validation and scaling of sophisticated physical and numerical fluvial hydraulic models to real field conditions are limited by temporal and spatial constraints of field measurement technologies. These limitations increase when analyzing hydraulic properties of complex river forms such as submerged bedrock canyons. The analysis of flow under these conditions has demonstrated non-linear behavior, strong secondary circulation and a high level of turbulence. The objective of this paper is to obtain and analyze turbulence and secondary current information for flow analysis, by evaluating the spatial distribution of bed shear stress and eddy viscosity with acoustic Doppler current profiler (ADCP) measurements. The real field-scale case study was the Lourenço Rock Canyon in Tocantins River, Brazil. A total of 10,531 velocity profiles were measured with an ADCP adapted to a moving boat. The data were post-processed by decomposing the velocity data measurements and calculating the standard deviations. Three different methods are compared for bed shear stress: total kinetic energy (TKE), law of the wall and the depth–slope product. The eddy viscosity was estimated with the Boussinesq approach. The initial data processing confirmed turbulence and flow velocity characteristics described in similar literature findings. The results for the bed shear stress for the canyon area were 8 times greater than the outside and for eddy viscosity, 10 times higher. For the surroundings area, the eddy viscosity showed reasonable results with values around the regular 1.0 m2/s used for rivers. It is concluded that turbulent values can be calculated to better represent physical processes with the intention to improve hydrodynamic numerical models calibrations.

Upper Ocean Response to Typhoon Kalmaegi and Sarika in the South China Sea from Multiple-Satellite Observations and Numerical Simulations

We investigated ocean surface and subsurface physical responses to Typhoons Kalmaegi and Sarika in the South China Sea, utilizing synergistic multiple-satellite observations, in situ measurements, and numerical simulations. We found significant typhoon-induced sea surface cooling using satellite sea surface temperature (SST) observations and numerical model simulations. This cooling was mainly caused by vertical mixing and upwelling. The maximum amplitudes were 6 °C and 4.2 °C for Typhoons Kalmaegi and Sarika, respectively. For Typhoon Sarika, Argo temperature profile measurements showed that temperature response beneath the surface showed a three-layer vertical structure (decreasing-increasing-decreasing). Satellite salinity observations showed that the maximum increase of sea surface salinity (SSS) was 2.2 psu on the right side of Typhoon Sarika’s track, and the maximum decrease of SSS was 1.4 psu on the left. This SSS seesaw response phenomenon is related to the asymmetrical rainfall on both sides of the typhoon track. Acoustic Doppler Current Profilers measurements and numerical simulations both showed that subsurface current velocities rapidly increased as the typhoon passed, with peak increases of up to 1.19 m/s and 1.49 m/s. Typhoon-generated SST cooling and current velocity increases both exhibited a rightward bias associated with a coupling between typhoon wind-stress and mixed layer velocity.

Sensitivity analysis of sediment flux derived by laser diffraction and acoustic backscatter within a reservoir

A combination of two indirect methods to measure sediment flux is presented in this study to evaluate suspended sediment transport in a hydropower reservoir. The acoustic backscatter signal (ABS) from an Acoustic Doppler Current Profiler (ADCP) is therefore applied in pre-defined transects within the reservoir in combination with a Laser In-Situ Scattering Transmissometry – stream lined device (LISST-SL). The stationary LISST-SL derived suspended sediment concentration (SSC) measurements are used to calibrate the ABS. From the LISST-SL measurements a time series of SSC is obtained. This enables, in addition, a comprehensive data analysis to evaluate the influence of natural fluctuations of the SSC on the calculated sediment flux, which should be taken into account when assessing sediment transport. Furthermore SSC measurements are done with the LISST-SL close to the reservoir bed. In areas close to the bed no information regarding the ABS is available from the ADCP measurements due to the side-lobe interference. In various studies the information from the last three valid cells is used for extrapolation. However, as result of a comparison of the LISST-SL measurements with extrapolated SSC values from the ADCP measurements it can be seen that, especially in deep reservoirs, this method has to be adapted to the in-situ conditions.

Seasonality of the Mindanao Current/Undercurrent System

AbstractSeasonality of the Mindanao Current (MC)/Undercurrent (MUC) system is investigated using moored acoustic Doppler current profiler (ADCP) measurements off Mindanao (8°N, 127.05°E) and ocean model simulations. The mooring observation during December 2010 to August 2014 revealed that the surface‐layer MC between 50–150 m is dominated by annual‐period variation and tends to be stronger in spring (boreal) and weaker in fall. Prominent semiannual variations were detected below 150 m. The lower MC between 150 and 400 m is stronger in spring and fall and weaker in summer and winter, while the northward MUC below 400 m emerges in summer and winter and disappears in spring and fall. In‐phase and out‐of‐phase current anomalies above and below 150 m were observed alternatively. These variations are faithfully reproduced by an eddy‐resolving ocean model simulation (OFES). Further analysis demonstrates that seasonal variation of the MC is a component of large‐scale upper‐ocean circulation gyre, while current variations in the MUC layer are confined near the western boundary and featured by shorter‐scale (200–400 km) structures. Most of the MC variations and approximately half of the MUC variations can be explained by the first and second baroclinic modes and caused by local wind forcing of the western Pacific. Semiannual surface wind variability and superimposition of the two baroclinic modes jointly give rise to the enhanced subsurface semiannual variations. The pronounced mesoscale eddy variability in the MUC layer may also contribute to the seasonality of the MUC through eddy‐current interaction.

Observed sediment and solute transport from the Kangerlussuaq sector of the Greenland Ice Sheet (2006–2016)

ABSTRACT New measurements of Watson River sediment and solute concentrations and an extended river discharge record improved by acoustic Doppler current profiler (ADCP) measurements are used to calculate the total sediment and solute transport from a large ice-sheet sector in southern west Greenland. For the 2006–2016 period, the mean annual sediment and solute transport was 17.5 ± 7.2 × 106 t and 85 ± 30 × 103 t, respectively (standard deviation given). The highest annual transport occurred in 2010, attaining values of 29.6 × 106 t and 138 × 103 t, respectively. The corresponding annual average values of specific transport are 1.39 × 103 t km−2 a−1 for sediment and 6.7 t km−2 a−1 for solutes from the approximately 12,600 km2 (95% ice covered) catchment, yielding an area-average erosion rate of 0.5 mm a−1. The specific transport is likely several times higher under the ice sheet near the margin where all meltwater passes than it is in the interior where the ice sheet is frozen to the bed. We conclude that the Greenland Ice Sheet is a large supplier of sediment and solutes to the surrounding fjords and seas. We find that the proglacial area can be a net source of sediments during high floods and we confirm that an increased amount of meltwater-transported sediments can explain the expansion of deltas around Greenland, contradictory to delta erosion observed elsewhere in the Arctic in recent years.

Incorporating Wave Spectrum Information in Real-time Free-surface Elevation Forecasting: Real-sea Experiments

Real-time prediction of free-surface elevation is necessary for a variety of applications. Assuming a Gaussian wave field, the wave spectrum can be used to calculate the statistically-optimal predictor, for a given prediction configuration (i.e. for a given combination of measurement instants and spatial locations, relative to the instants and locations where and when the wave is predicted). More specifically, the optimal predictor is linear, and its coefficients need only be updated as the wave condition evolves. This spectrum-based prediction (SBP) approach encompasses, in a unified theoretical framework, both “time-series” and “spatially-distributed” prediction configurations. In this paper, the validity of the SBP theoretical framework is tested against real-sea wave data, which originate from a measurement campaign using an Acoustic Doppler Current Profiler (ADCP), and consist of free-surface elevation time series, at the corners and centre of a 25m-by-25m square. The directional wave spectra, corresponding to the sea states where the time series are provided, have also been calculated. The empirical SBP accuracy, obtained by applying the SBP in the real-sea time series, is assessed in various sea conditions and prediction configurations, and compared with the theoretical SBP accuracy, evaluated based on the wave spectra. Although the ADCP measurement layout is clearly not ideal for the purpose of wave forecasting, empirical results are physically and statistically consistent, and show good agreement with theoretical results, thus supporting the relevance of the SBP framework.

Hydrography and circulation west of Sardinia in June 2014

Abstract. In the frame of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD (conductivity, temperature, depth) instruments, towed devices, and vessel-mounted ADCPs (acoustic doppler current profilers), are presented and compared with previous knowledge. So far, the circulation is not well-known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m−3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72<σΘ/(kg m−3) < 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15′ E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s−1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transports of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition.

BAM: Bayesian AMHG‐Manning Inference of Discharge Using Remotely Sensed Stream Width, Slope, and Height

AbstractThe forthcoming Surface Water and Ocean Topography (SWOT) NASA satellite mission will measure water surface width, height, and slope of major rivers worldwide. The resulting data could provide an unprecedented account of river discharge at continental scales, but reliable methods need to be identified prior to launch. Here we present a novel algorithm for discharge estimation from only remotely sensed stream width, slope, and height at multiple locations along a mass‐conserved river segment. The algorithm, termed the Bayesian AMHG‐Manning (BAM) algorithm, implements a Bayesian formulation of streamflow uncertainty using a combination of Manning's equation and at‐many‐stations hydraulic geometry (AMHG). Bayesian methods provide a statistically defensible approach to generating discharge estimates in a physically underconstrained system but rely on prior distributions that quantify the a priori uncertainty of unknown quantities including discharge and hydraulic equation parameters. These were obtained from literature‐reported values and from a USGS data set of acoustic Doppler current profiler (ADCP) measurements at USGS stream gauges. A data set of simulated widths, slopes, and heights from 19 rivers was used to evaluate the algorithms using a set of performance metrics. Results across the 19 rivers indicate an improvement in performance of BAM over previously tested methods and highlight a path forward in solving discharge estimation using solely satellite remote sensing.