The paper presents the current status of the Maritime Aerosol Network (MAN), which has been developed as a component of the Aerosol Robotic Network (AERONET). MAN deploys Microtops handheld Sun ...photometers and utilizes the calibration procedure and data processing (Version 2) traceable to AERONET. A web site dedicated to the MAN activity is described. A brief historical perspective is given to aerosol optical depth (AOD) measurements over the oceans. A short summary of the existing data, collected on board ships of opportunity during the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project is presented. Globally averaged oceanic aerosol optical depth (derived from island‐based AERONET measurements) at 500 nm is ∼0.11 and Angstrom parameter (computed within spectral range 440–870 nm) is calculated to be ∼0.6. First results from the cruises contributing to the Maritime Aerosol Network are shown. MAN ship‐based aerosol optical depth compares well to simultaneous island and near‐coastal AERONET site AOD.
Regions Of Freshwater Influence (ROFI) are of particular interest in a source-to-sink approach in terms of sediment advection, settling, and deposition in the coastal zone. An experiment was carried ...out in the ROFI of the Rhône River in February 2016 to describe the properties of suspended particulate matter (SPM) during a flood event. A digital holographic camera (LISST-HOLO, 20–2000 μm) was used to estimate the variability of fine sediment floc properties (size, nature and shape) formed in the Rhône mouth. An automatic image toolbox was developed to classify the different constituents of the SPM (as diatoms, bubbles and flocs) and to describe the diversity of floc shapes existing in the material in suspension. We estimated the fractal dimension (DF3D), the aspect ratio (AR) and the settling velocity of flocs (Ws). The estimated DF3D ranged between 2.0 and 2.5 highlights the complexity of floc shape, which was used as a proxy of the flocculation mechanism functioning in the Rhône mouth. Additionally, we performed a sensitivity analysis on the estimate of Ws using different shape-related coefficients (α/β) and primary particle size (dP). The results highlighted the impact of the flocculation of fine sediments on the increase of Ws from 0.01 to 3 mm s−1 when floc sizes increase from 30 to 500 μm. Ws showed a decrease of 41% considering the sphericity of flocs that emphasized the need to consider the floc shape to properly estimate their settling velocity. We showed that an increase of dP from 1 to 12 μm induces a fivefold increase of Ws that showed the need for an adequate system to properly estimate the size of primary particles. These results emphasized the need to take into account such variability in future model of floc dynamics in ROFI to properly estimate plume sinking rate and SPM dynamics.
•Description of fine sediment floc properties in the Rhône River ROFI.•Evidence of the diversity of floc shapes existing in the material in suspension.•Flocculation increases of two orders the settling velocity of fine sediments.•Evidence of the decrease of floc settling velocities considering floc shapes.
Abstract
The study of the suspended particulate matter (SPM) transport is essential to understanding oceans and rivers, for their presence can impact the environment, from marine habitats or water ...quality degradations to important changes of the seabed morphology. Among a large number of surrogate techniques in traditional water sampling, acoustical methods have the advantage of providing nonintrusive measurements, with high spatial and temporal resolutions. However, the ability of fine-grained sediments to aggregate under the process of flocculation complexifies the interpretation of acoustical measurements. The objective of this paper is to design a simple backscattering model for flocculated sediment suspensions, in order to interpret the information provided by a multifrequency profiler and to retrieve both the concentration and the dominant size of a suspension of flocculated sediments in an estuarine context. In situ granulometry laser data, collected in the Aulne macrotidal estuary (France), showed that over the size distribution observed, a mean porosity of apparent particles in suspension can be used directly as input for model generation. The in situ acoustic signal was concurrently recorded at 0.5, 1, 2, and 4 MHz, and then inverted using the nonnegative least squares algorithm after constraining the model with an optimal porosity, allowing for a discrete representation of the mass concentration distributed over several equivalent spherical radii. The inversion results are in good agreement with the in situ mass concentration obtained through in situ water samplings.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The study of the suspended particulate matter (SPM) transport is essential to understanding oceans and rivers, for their presence can impact the environment, from marine habitats or water quality ...degradations to important changes of the seabed morphology. Among a large number of surrogate techniques in traditional water sampling, acoustical methods have the advantage of providing nonintrusive measurements, with high spatial and temporal resolutions. However, the ability of fine-grained sediments to aggregate under the process of flocculation complexifies the interpretation of acoustical measurements. The objective of this paper is to design a simple backscattering model for flocculated sediment suspensions, in order to interpret the information provided by a multifrequency profiler and to retrieve both the concentration and the dominant size of a suspension of flocculated sediments in an estuarine context. In situ granulometry laser data, collected in the Aulne macrotidal estuary (France), showed that over the size distribution observed, a mean porosity of apparent particles in suspension can be used directly as input for model generation. The in situ acoustic signal was concurrently recorded at 0.5, 1, 2, and 4 MHz, and then inverted using the nonnegative least squares algorithm after constraining the model with an optimal porosity, allowing for a discrete representation of the mass concentration distributed over several equivalent spherical radii. The inversion results are in good agreement with the in situ mass concentration obtained through in situ water samplings.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Due to complex natural and anthropogenic forcings, the dynamics of suspended sediments within the ocean water column remains difficult to monitor. Nowadays however, more and more available ...information is coming from in situ and satellite measurements, as well as from simulation models. Data assimilation methods propose to combine all this information to produce the most precise results, allowing better analyzes of the processes in play. Here a comparison of data-driven methods is presented. Optimal Interpolation (OI), Empirical Orthogonal Function (EOF) based and Kalman Filter based methods are compared to a new one using neural networks. The latter is a Data Interpolation method based on convolutional AutoEncoders (DinAE). Present results show that DinAE better performs compared to other methods, having the lowest error budget and the highest learning of high frequency events.
Characterization of suspended sediment dynamics in the coastal ocean provides essential information for scientific studies and operational challenges concerning, among others, turbidity, water ...transparency and the development of microorganisms using photosynthesis, which is critical for primary production. The complexity of the processes involved in sediment dynamics makes it difficult to predict surface dynamics. In the continuity of previous experiments, the 4DVarNet model having shown encouraging results with SSSC interpolations, it is tested in a 20-day forecasting problem. In addition to the learning architecture including the missing observation data, a protocol has been conceptualized to integrate different types of forcing to improve the reconstructions. The results of the method show that it is possible to produce satisfactory results. The results of the method show that it is possible to produce satisfactory results. The contribution of the input forcing is notable improving of 20% precision horizons. The study also highlights a characterization of the different input forcing and their effect on the system.
Many different instruments directly or indirectly observe the oceanic tidal movements. Among them, we consider here the coastal tide gauge and deep‐sea pressure recorder which provide at least the ...principal spectral constituents of the tidal height, the gravimeter which indirectly observes the oceanic tides through the gravitational effect generated by the deformation of the solid Earth under the ocean tidal mass load, and the satellite altimeter which samples the tides in the time domain and over the nearly whole ocean. Our present paper deals with an empirical method for the recovery of the oceanic tides by inversion of heterogeneous data sets. The aim is to take advantage of the different kinds of information coming from the measurement instruments in order to complete more accurate empirical solutions. First, tide gauge and gravity loading data are separately and jointly inverted to provide global charts of the major semidiurnal M2 wave. The results prove that the tide gauge data have a major contribution in the tidal mapping but also suggest that the gravity loading data distort the information. This is certainly due to unmodelled geophysical phenomena and instrumental errors. Second, tide gauge and satellite altimeter data are considered in a separate and a joint inversion computation to provide tidal estimations along a predefined geographical line in the North Atlantic. The results are accurate enough to make provision for the boundary conditions of an hydrodynamical tidal model. As an intrinsic advantage of the inversion method, a posteriori standard deviations and error covariances for all the solutions displayed are provided and analyzed.
Optical remote sensing is increasingly used to assess various sea surface biogeochemical parameters (e.g., Chl-a 1 , turbidity 2 ). If today's systems offer a better spatiotemporal coverage, it still ...depends on both the satellite revisit period and the cloud cover at the time of the acquisition. The resulting sea surface observations generally present large proportions of missing data, limiting their use. Typically, in our experiments, we worked with datasets containing up to 98% of missing data.
Among the various missions assigned to the SHOM and responding to the French Navy and public administration requests (involved in environmental affairs), one of the recent objectives is to ensure ...better knowledge of the continental maritime area. Among coastal projects, the one we deal in this study consists in evaluating the optical properties of shelf waters. This project called "Turbidity" focuses more particularly on turbidity processes having an impact on submarine visibility. This project is structured around three topics: (1) spatial and in-situ observations of the turbidity, (2) acoustic measurements for detection of particles loads and (3) a modelling approach. The modelling theme, presented here, involves development of simulation tools coupling hydrodynamics (the physical frame is provided by the MARS3D model developed by Ifremer), biological and sedimentary dynamics (provided by the model SiAM3D developed by Ifremer). An optical model completes this tool, in order to convert the turbidity parameters in terms of submarine visibility. The actual configuration of the model simulates the turbid waters above the French Atlantic continental shelf. The project includes also an adaptation of this framework to the Persian gulf area. The model takes into account the mineral and organic (living and non-living) particles which influence the optical properties of water. The biological production follows specific conditions of light, nutrients inputs and ocean dynamics. And the mineral particles are coming from river discharges and exchanges fluxes with the sediment (erosion and deposit). The complexity of the processes requires a modelling approach. At this complexity of particles origin, adds the complexity of the circulation of waters masses and particulate transport in coastal area (dynamic of freshwater plumes, gradients of water's density, influence of mixing by winds, tides and waves, and interactions of these processes with coastline and bathymetry). Consistent with the observations, the model reproduces reasonably well the main algal and mineral seasonal structures. The two mains axes planned to improve quantitative assessment are (1) the modelling of particulate structures and (2) the optical model: (1) modelling presents encouraging results but is actually limited by a coarse spatial resolution of the model, by simplified forcing fluxes (wave, wind and sunshine) and by simplified hydro-sedimentary and biological schemes; (2) the optical module is based on empirical laws coming from literature and is limited to a monochromatic approach; however, in-situ measurements cruises are planned in order to be suited to the specific characteristics of the study areas. The difficulty of this feasibility study is based on the fact that neither in-situ measurements, nor model estimations are directly linked to the visibility parameters. In-situ, visibility is assessed with the measurement of inherent optical properties. With the model, it is deduced from the particles concentrations. Moreover, the biological and sedimentary transport models are not able to reproduce the whole nature and multitude of particles and molecules influencing the optical properties. All this makes the visibility distances difficult to assess.
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