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Remote sensing has been used to map river bathymetry for several decades. Non-contact methods are necessary in several cases: inaccessible rivers, large-scale depth mapping, very shallow rivers. The remote sensing techniques used for river bathymetry are reviewed. Frequently, these techniques have been developed for marine environment and have then been transposed to riverine environments. These techniques can be divided into two types: active remote sensing, such as ground penetrating radar and bathymetric lidar; or passive remote sensing, such as through-water photogrammetry and radiometric models. This last technique which consists of finding a logarithmic relationship between river depth and image values appears to be the most used. Fewer references exist for the other techniques, but lidar is an emerging technique. For each depth measurement method, we detail the physical principles and then a review of the results obtained in the field. This review shows a lack of data for very shallow rivers, where a very high spatial resolution is needed. Moreover, the cost related to aerial image acquisition is often huge. Hence we propose an application of two techniques, radiometric models and through-water photogrammetry, with very high-resolution passive optical imagery, light platforms, and off-the-shelf cameras. We show that, in the case of the radiometric models, measurement is possible with a spatial filtering of about 1 m and a homogeneous river bottom. In contrast, with through-water photogrammetry, fine ground resolution and bottom textures are necessary.

Airborne lidar systems (ALS) provide 3D point clouds of the topography by direct time measurement of a short laser pulse after reflection on the Earth surface. For the last decade, this technique has proved to be the ideal remote sensing tool for delivering very accurate digital terrain model (DTM) of the Earth surface, and then for answering main environmental issues such as natural hazard prevention and natural ressource management. Moreover, such active systems, also called multiple echo lidar, allow to detect several return signals for a single laser shot. It is particularly relevant in case of vegetation areas since a single lidar survey allows to acquire not only the canopy top (the only visible layer from passive sensors), but also points inside the vegetation layer and on the ground underneath. Thus, among the different remote sensing techniques, airborne laser scanning has also proved to be the most efficient technique to characterize both forest structure and ground topography. For a few years, new airborne laser scanning systems called full-waveform lidar systems have emerged, providing not only 3D point clouds as classical ALS systems, but entire altimeter profiles of reflected energy from the Earth surface. These profiles represent the laser backscattered energy as a function of time. They give to the end-user more control and flexibility on the signal processing steps and enable to extract more information than classical multi-echo lidar data. A detailed state-of-the-art of such systems can be found in [1]. However, managing these data with spacial and time dependency is much more complex than images or 3D point clouds : raw full-waveform lidar data are sets of range profiles of various lengths that are stored in the sensor geometry following both the scan angle of the lidar system and the chronological order along the flight track. Moreover, the data volume is drastically larger than 3D point clouds: it takes about 140 GB for an acquisition time of 1.6 h with a pulse repetition frequency (PRF) of 50kHz. Furthermore, there is neither commercial nor opensource toolkit to handle full-waveform lidar data, but some constructor solutions, that are black boxes, can only extract 3D point clouds from raw data and are designed to their own sensors. Finally, there is not standard file format for full-waveform data (such as the LAS format for multi-echo data). Managing full-waveform lidar data is therefore a challenging task, and we adress this issue by developping a specific research tool: FullAnalyze.

The East Demerara Water Conservancy (EDWC) and east coast drainage and irrigation systems provide water storage and flood control mechanisms for Guyana's most populous region, including the capital city of Georgetown. In 2005, extreme rainfall caused devastang flooding along these coastal lowlands, with many areas remaining inundated for up to three weeks. The flood highlighted the vulnerability of the EDWC dam to overtopping and potential breaching. The Conservancy Adaptation Project (CAP) was conceived in the wake of the 2005 flood to help the Government of Guyana adapt to the threats posed by future climate change. The aim was to reduce the likelihood of catastrophic flooding along Guyana's low-lying coastal areas, also threatened by sea level rise. The project identified key investments totaling over US$ 123 million. These are being used by the Government to update the national master-plan strategy for drainage and irrigation and to plan future investment programs for reducing flood risk.

Estimating river discharge from in situ and/or remote sensing data is a key issue for evaluation of water balance at local and global scales and for water management. Variational data assimilation (DA) is a powerful approach used in operational weather and ocean forecasting, which can also be used in this context. A distinctive feature of the river discharge estimation problem is the likely presence of significant uncertainty in principal parameters of a hydraulic model, such as bathymetry and friction, which have to be included into the control vector alongside the discharge. However, the conventional variational DA method being used for solving such extended problems often fails. This happens because the control vector iterates (i.e., approximations arising in the course of minimization) result into hydraulic states not supported by the model. In this paper, we suggest a novel version of the variational DA method specially designed for solving estimation-under-uncertainty problems, which is based on the ideas of iterative regularization. The method is implemented with SIC2, which is a full Saint-Venant based 1D-network model. The SIC2 software is widely used by research, consultant and industrial communities for modeling river, irrigation canal, and drainage network behavior. The adjoint model required for variational DA is obtained by means of automatic differentiation. This is likely to be the first stable consistent adjoint of the 1D-network model of a commercial status in existence. The DA problems considered in this paper are offtake/tributary estimation under uncertainty in the cross-device parameters and inflow discharge estimation under uncertainty in the bathymetry defining parameters and the friction coefficient. Numerical tests have been designed to understand identifiability of discharge given uncertainty in bathymetry and friction. The developed methodology, and software seems useful in the context of the future Surface Water and Ocean Topography satellite mission.

This report is the primary output from the climate change impact and adaptation study for the Bangkok Metropolitan Region (BMR) produced for the Bangkok Metropolitan Administration (BMA) with financial support provided by the World Bank. The report concerns climate change, and provides an analysis of climate change impacts and adaptation options for the BMR. In addition to the more general matters on the physical setting and socioeconomics of BMR, the report considers a number of issues related to climate change in detail. These are: changes in the inundation pattern, and impact on the population and socioeconomics, and coping mechanisms to deal with the changed situation.

During the past few years there was an increasing demands of needs for mapping the bottom of water, either because it was needed for Navigation Safety, Nautical charts, or for Pollution controlling, mineral and fish industries. Over the years the methods of bathymetry and mapping showed a huge improvement especially in the last 40 years where a rapid growth occurs in this part of science. Particular growth occurs in the bathymetry area using satellite data which continuously presented and exported new models in order to create maps in a shorter time period and with fewer expenses. Additionally there is an increasing improvement in the accuracy of the results of the maps over time and it is accomplished with smaller errors. For export of maps and finding data followed a fairly complicated process which needs to take into account many parameters are either located in the constituents of water, either the nature of the water bottom, or in the atmosphere and beyond. The method of remote sensing is divided into two main categories imagine methods and the Non imagine methods. Both are widely known, in conclusion, the methodology of remote sensing comparatively with the eco-sounding method is more efficient in a matter of time, financial budget, data accuracy than any other method exists, and usually is recommended for use. Πάντα υπήρχε η ανάγκη της χαρτογράφησης του πυθμένα του νερού, είτε ο λόγος αυτός αφορούσε την ασφαλή ναυσιπλοία είτε αφορούσε τον έλεγχο της στάθμης του νερού ή αφορούσε περιβαλλοντικούς λόγους. Κατά την πάροδο των χρόνων οι μέθοδοι της βυθομέτρησης και της χαρτογράφησης εξελίσονταν και βελτιώνονταν, ειδικά τα τελευταία 40 χρόνια όπου παρουσιάζεται μία ραγδαία ανάπτυξη στον τομέα αυτό. Ιδιαίτερη ανάπτυξη παρουσιάζεται στον τομέα της βυθομετρίας με την χρήση δορυφορικών δεδομένων όπου συνεχώς παρουσιάζονται νέοι τρόποι εξαγωγής χαρτών σε συντομότερο χρόνο και με λιγότερες δαπάνες. Επιπρόσθετα διακρίνεται μία συνεχής βελτίωση στην ακρίβεια των αποτελεσμάτων καθώς με τον καιρό επιτυγχάνεται η εξαγωγή αποτελεσμάτων με μεγαλύτερες ακρίβειες συνεπώς με μικρότερα σφάλματα. Για την εξαγωγή των χαρτών και την εύρεση των δεδομένων ακολουθείται μία αρκετά περίπλοκη διαδικασία όπου χρειάζεται να λαμβάνονται υπόψη πολλοί παραμέτροι είτε αυτοί βρίσκονται στα συστατικά του νερού, είτε στο είδος του πυθμένα του νερού, είτε στην ατμόσφαιρα και όχι μόνο. Η μέθοδος της τηλεπισκόπησης διακρίνεται σε δύο βασικές κατηγορίες η μέθοδος απικόνησης και η μέθοδος μη απικόνησης. Είναι και οι δύο ευρέως γνωστές. Εν κατακλείδι, η μέθοδολογία της τηλεπισκόπησης είναι πιο αποδοτική σε θέμα χρόνου, οικονομικού προυπολογισμού, ακρίβεια δεδομένων σε σχέση με οποιαδήποτε άλλη μέθοδο υπάρχει, και συνήθως είναι αυτή που συστήνεται για χρήση. Completed

The knowledge of bathymetry and topography immerged surfaces, is crucial point in improvement knowledge of surroundings aquatic seashore and continental (modeling ecosystem, mapping, modeling hydrology system). For the purpose of estimate topography on river's long linear, LiDAR Bathymetric appears as specially adapted technological. However,there are some references on the precision of this technique within the framework of the littoral zones, but there is little of references precises on continental waters. To estimate from the theoretical point of view the limits of the LiDAR Bathymetric is a first approach to a appreciate the transfer of this technique towards continental waters. This evaluation has to concern for rivers the limit of discrimination of the blade of water for very weak depthes, and it for blades of water which can be pent. To make these theoretical studies through the analysis of wave trains laser return feigned (power return according to time) with the peculiarities of rivers, appears as the most adapted approach. The made study took place in two phases : the first one concerned the modelling then the simulation of wave trains for various parameters of rivers ; one second was interested in the inversion of wave trains feigned to find the thickness of water. This inversion was realized by estimate of a mixture of laws of probability. For the part simulation, we notice on the feigned wave trains that the roughness of the surface and the bottom of the river, pull a modification of the amplitude of the power, allowing a better distinction between surface and bottom ; on the other hand the maximal hillsides of the surface and the bottom of the river, have no important effects on the shape of the wave train, what facilitates the detection. For the part inversion, the limit obtained from discrimination of the blade of water, for a surface and a flat bottom, is situated as deep as 50 cm ; on the other hand for a surface and a rough bottom, it is situated as deep as 30 cm. We also observe that the measures of detection of the depth, are little sensitive to the parameters of the system LiDAR. / La connaissance de la bathymétrie et de la topographie des surfaces immergées est un point d'entrée incontournable dans l'amélioration de la connaissance des milieux aquatiques littoraux et continentaux (modélisation des écosystèmes, cartographie, modélisation des hydrosystèmes). Pour l'estimation de la topographie sur de grands linéaires de fleuves et rivières, le LiDAR bathymétrique apparaît comme une technique particulièrement adaptée. Cependant, s'il existe quelques références sur la précision de cette technique dans le cadre des zones littorales, peu de références précises existent sur les eaux continentales. Evaluer du point de vue théorique les limites du LiDAR Bathymétrique est une première approche pour apprécier le transfert de cette technique vers les eaux continentales. Cette évaluation doit porter pour les fleuves et rivières sur la limite de discrimination de la lame d'eau pour de très faibles profondeurs, et ce pour des lames d'eau qui peuvent être pentues. Effectuer ces études théoriques à travers l'analyse de trains d'ondes laser retour simulés (puissance retour en fonction du temps) avec les particularités des rivières, apparaît comme l'approche la plus adaptée. L'étude effectuée s'est déroulée en deux phases : une première a porté sur la modélisation puis la simulation de trains d'ondes pour différents paramètres de rivières ; une seconde s'est intéressée à l'inversion de trains d'ondes simulés pour retrouver l'épaisseur d'eau. Cette inversion a été réalisée par approximation d'un mélange de lois de probabilités. Pour la partie simulation, on s'aperçoit sur les trains d'ondes simulés que la rugosité de la surface et du fond de la rivière, entraînent une modification de l'amplitude de la puissance, permettant une meilleure distinction entre surface et fond ; en revanche les pentes maximales de la surface et du fond de la rivière, n'ont pas d'effets importants sur la forme du train d'ondes, ce qui facilite la détection. Pour la partie inversion, la limite obtenue de discrimination de la lame d'eau, pour une surface et un fond plat, se situe à 50 cm de profondeur ; en revanche pour une surface et un fond rugueux, elle se situe à 30 cm de profondeur. On observe également que les mesures de détection de la profondeur, sont peu sensibles aux paramètres du système LiDAR.

Space-borne instruments can measure river water surface elevation, slope and width. Remote sensing of river discharge in ungauged basins is far more challenging, however. This work investigates the estimation of river discharge from simulated observations of the forthcoming Surface Water and Ocean Topography (SWOT) satellite mission using a variant of the classical variational data assimilation method "4D-Var". The variational assimilation scheme simultaneously estimates discharge, river bathymetry and bed roughness in the context of a 1.5D full Saint Venant hydraulic model. Algorithms and procedures are developed to apply the method to fully ungauged basins. The method was tested on the Po and Sacramento Rivers. The SWOT hydrology simulator was used to produce synthetic SWOT observations at each overpass time by simulating the interaction of SWOT radar measurements with the river water surface and nearby land surface topography at a scale of approximately 1 m, thus accounting for layover, thermal noise and other effects. SWOT data products were synthesized by vectorizing the simulated radar returns, leading to height and width estimates at 200 m increments along the river centerlines. The ingestion of simulated SWOT data generally led to local improvements on prior bathymetry and roughness estimates which allowed the prediction of river discharge at the overpass times with relative root-mean-squared errors of 12.1% and 11.2% for the Po and Sacramento rivers respectively. Nevertheless, equifinality issues that arise from the simultaneous estimation of bed elevation and roughness may prevent their use for different applications, other than discharge estimation through the presented framework.

Seamounts are isolated elevations in the seafloor with circular or elliptical plans, comparatively steep slopes, and relatively small summit areas (Menard, 1964). The vertical gravity gradient (VGG), which is the curvature of the ocean surface topography derived from satellite altimeter measurements, has been used to map the global distribution of seamounts (Kim and Wessel, 2011). We used the latest grid of VGG to update and refine the global seamount catalog; we identified 10,796 new seamounts, expanding the catalog by 1/3. 739 well-surveyed seamounts, having heights ranging from 421 m to 2500 m, were then used to estimate the typical radially-symmetric seamount morphology. First, an Empirical Orthogonal Function (EOF) analysis was used to demonstrate that these small seamounts have a basal radius that is linearly related to their height – their shapes are scale invariant. Two methods were then used to compute this characteristic base to height ratio: an average Gaussian fit to the stack of all profiles and an individual Gaussian fit for each seamount in the sample. The first method combined the radial normalized height data from all 739 seamounts to form median and median-absolute deviation. These data were fitted by a 3-parameter Gaussian model that explained 99 percent of the variance. The second method used the Gaussian function to individually model each seamount in the sample and further establish the Gaussian model. Using this characteristic Gaussian shape, we show that VGG can be used to estimate the height of small seamounts to an accuracy of about 270 m.

The knowledge of immerged surfaces bathymetry and topography is a crucial point for sustainable management of seashore and continental aquatic areas. Bathymetric LiDAR appears as an adapted technology for river measurement. Nevertheless, evenif it exists some references on this technique's precision on costal areas, few exist on continental waters. This study took place in Cemagref, in a sustainable management of continental water context, in order to make compatible biodiversity conservation and human use. Its objective is to look forward a transfert of LiDAR technology to rivers. The study in parsed in four stages. The rst one is the nalisation of a bathymetric LiDAR waveforms modeling tool developed in the R software. With this tool, we deduced a minimum depth detectable by LiDAR at 42 cm, and bring to the light the existance of an optimal water surface roughness in terms of measure quality. In a second time, I present my work on visualisation tools développement for bathymetric LiDAR data and waveforms in a contract framework with the French national hydrographic service (SHOM). Data were gathered in 2005 on the Golfe du Morbihan with a SHOALS system. It represents for us a rst approach of bathymetric LiDAR measurement. Third, I present my work on signal processing. I developed algorithms in order to re-estimate non detected depths. Whereas shallow waters detection was not the main objective of the Morbihan gathered, my algorithms enhanced the minimum depth detection limit of 80 cm, without reducing precision. Then, we I introduce the LiDAR test we did on 2 km of Gardon river with an HawkEye system. It shows the LiDAR ability to map the river with a precision of 32,1 cm and a minimum detectable depth around 40 cm. / La connaissance de la bathymétrie et de la topographie des surfaces immergées est primordiale en vue d'une gestion durable des milieux aquatiques littoraux et continentaux. Par sa rapidité d'exécution, le LiDAR bathymétrique apparaît comme une technique particulièrement adaptée à la mesure de rivières. Cependant, s'il existe de nombreuses références sur la précision de cette technique sur les zones littorales, peu existent sur les eaux continentales. L'étude présentée dans ce rapport a pris place au Cemagref, dans un contexte de gestion durable de eaux continentales, an concilier conservation du patrimoine biologique et prise en compte des dirents usages. Elle a pour objectif de se pencher sur un éventuel transfert de la technologie LiDAR vers les rivières. Elle est composée de quatre parties. Dans la première, je présente mon travail sur la nalisation d'un outil de modélisation de trains d'ondes LiDAR bathymétrique. Cet outil, développé sous le logiciel R a permis d'estimer à 42 cm le profondeur d'eau minimale détectable par le LiDAR, et de montrer l'existence d'une rugosité de surface optimale pour la qualité de la mesure. Dans la seconde je présente mon travail sur le développement d'outils de visualisation de données et trains d'ondes LiDAR bathymétrique dans le cadre d'un contrat avec le Service Hydrographique et Océanographique de la Marine (SHOM). Ces données ont été acquises en 2005 sur le Golfe du Morbihan avec un capteur SHOALS et représentent pour nous une première approche de la mesure par LiDAR bathymétrique. Dans la troisième, je me penche sur l'analyse du signal LiDAR que j'ai ectuée. Pour cela j'ai développé des algorithmes de traitement avec pour objectif de ré-estimer des profondeurs non détectées par les algorithmes du prestataire. Bien que les zones faiblement profondes n'étaient pas la priorité du levé, mes algorithmes améliorent de 80 cm la limite minimale détectée, avec la même pré-cision de mesure. Enn, je présente les résultats de l'essai LiDAR que nous avons ectué sur 2 km du Gardon à l'aide du capteur suédois HawkEye. Ils font ressortir une capacité du système à cartographier le lit de la rivière avec une précision de 32,1 cm et une profondeur minimale détectable aux alentours de 40 cm.