On the use of the Radon transform to estimate longshore currents from video imagery

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On the use of the Radon transform to estimate longshore currents from video imagery

In nearshore applications, the estimation of longshore currents is of primary importance since it controls the alongshore sediment transport and coastal evolution. Direct estimation of longshore currents using in-situ instruments is difficult and costly, especially under highly energetic wave climates. Low cost remote sensing systems based on video observations constitute a promising alternative when the drifting sea foam left after the passage of breaking waves is visible. In this paper we describe a method based on longshore timestacks that necessitates less data than approaches using the full video frames. Our approach uses the Radon transform applied on the time series derived from timestacks to produce an estimate of the longshore component of nearshore surface currents detected from the foam signature in video images. The Radon transform can be used to separate the wave crests from the drifting foam part. The identification of the longshore drift is enhanced with both a temporal and a spatial filters. The corresponding sinogram from the Radon transform is computed in order to find the angle of the alongshore drifting that is further converted into the longshore component of the surface currents. For the estimation of longshore currents, our approach is first tested using synthetic timestack examples created using anisotropic Gaussian random current fields. Comparisons between estimates derived by our algorithm and manual operator detection from videos are performed showing good agreement. These videos come from a field campaign conducted in the Mataquito River mouth area in the Maule region (Chile). Field test comparisons were also made against in situ current meter from the 2008 True Vert experiment in Aquitaine (France). It was taking place during an energetic event

Estimation of Multiple Inflows and Effective Channel by Assimilation of Multi-satellite Hydraulic Signatures: The Ungauged Anabranching Negro River

International audienceWith the upcoming SWOT satellite mission, which should provide spatially dense river surface elevation, width and slope observations globally, comes the opportunity to assimilate such data into hydrodynamic models, from the reach scale to the hydrographic network scale. Based on the HiVDI (Hierarchical Variational Discharge Inversion) modeling strategy (Larnier et al. [#Larnier2019]), this study tackles the forward and inverse modeling capabilities of distributed channel parameters and multiple inflows (in the 1D Saint-Venant model) from multisatellite observations of river surface. It is shown on synthetic cases that the estimation of both inflows and distributed channel parameters (bathymetry-friction) is achievable with a minimum spatial observability between inflows as long as their hydraulic signature is sampled. Next, a real case is studied: 871 km of the Negro river (Amazon basin) including complex multichannel reaches, 21 tributaries and backwater controls from major confluences. An effective modeling approach is proposed using (i) WS elevations from ENVISAT data and dense in situ GPS flow lines (Moreira [#DanielPhD]), (ii) average river top widths from optical imagery (Pekel et al. [#Pekel_Nature]), (iii) upstream and lateral flows from the MGB large-scale hydrological model (Paiva et al. [#paiva2013]). The calibrated effective hydraulic model closely fits satellite altimetry observations and presents real like spatial variabilities; flood wave propagation and water surface observation frequential features are analyzed with identifiability maps following Brisset et al. [#Brisset_2018]. Synthetic SWOT observations are generated from the simulated flowlines and allow to infer model parameters (436 effective bathymetry points, 17 friction patches and 22 upstream and lateral hydrographs) given hydraulically coherent prior parameter values. Inferences of channel parameters carried out on this fine hydraulic model applied at a large scale give satisfying results using noisy SWOT-like data at reach scale. Inferences of spatially distributed temporal parameters (lateral inflows) give satisfying results as well, with even relatively small scale hydrograph variations being inferred accurately on this long reach. This study brings insights in: (i) the hydraulic visibility of multiple inflows hydrographs signature at large scale with SWOT; (ii) the simultaneous identifiability of spatially distributed channel parameters and inflows by assimilation of satellite altimetry data; (iii) the need for prior information; (iv) the need to further tailor and scale network hydrodynamic models and assimilation methods to improve the fusion of multisource information and potential information feedback to hydrological modules in integrated chains

The topological gradient method : from optimal design to image processing

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Prevention of edema and flight microangiopathy with Venoruton (HR), (0-[beta-hydroxyethyl]-rutosides) in patients with varicose veins.

The aim of this open study was the evaluation of the effects of HR (Venoruton) at a dose of 1 g/day on the prevention and control of flight microangiopathy and edema in subjects with varicose veins and moderate chronic venous insufficiency flying for more than 11 hours. Patients with varicose veins, edema, but without initial skin alterations or complications, were included. Measurements of skin laser Doppler (LDF) resting flux (RF) venoarteriolar response (VAR), ankle swelling (RAS), and edema were made within 12 hours before and within 3 hours after the flights. The resulting edema after the flights was evaluated with a composite edema score (analogue scale line). A group of 20 subjects was treated with HR (1 g/day, starting 2 days before the flight and 1 g for every 12 hours on day of travel). Another group of 18 subjects formed the control group. The length of the flights was between 11 and 13 hours; all seats were in coach class. Fifty patients were enrolled and 38 patients were evaluable at the end of the trial. The 2 groups (treatment and control) were comparable for age and sex distribution. The decrease in RF was significant in both groups with a higher flux at the end of the flight in the HR group (p < 0.05). The venoarteriolar response was decreased at the end of the flights; the decrease was lower in the HR group (p < 0.05). The increase in RAS and the edema score were significantly lower in the HR group. In conclusion HR is useful for reducing the level of microangiopathy and the increased capillary filtration and in controlling edema in patients with venous disease in long flights. The higher level of flux and VAR and the reduction in edema indicate a positive effect of HR on the microcirculation. This study confirms that HR prophylaxis is effective to control flight microangiopathy associated with edema