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"Bertin, Stéphane"
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RTK GNSS-Assisted Terrestrial SfM Photogrammetry without GCP: Application to Coastal Morphodynamics Monitoring
2020
The present article describes a new and efficient method of Real Time Kinematic (RTK) Global Navigation Satellite System (GNSS) assisted terrestrial Structure-from-Motion (SfM) photogrammetry without the need for Ground Control Points (GCPs). The system only requires a simple frame that mechanically connects a RTK GNSS antenna to the camera. The system is low cost, easy to transport, and offers high autonomy. Furthermore, not requiring GCPs enables saving time during the in situ acquisition and during data processing. The method is tested for coastal cliff monitoring, using both a Reflex camera and a Smartphone camera. The quality of the reconstructions is assessed by comparison to a synchronous Terrestrial Laser Scanner (TLS) acquisition. The results are highly satisfying with a mean error of 0.3 cm and a standard deviation of 4.7 cm obtained with the Nikon D800 Reflex camera and, respectively, a mean error of 0.2 cm and a standard deviation of 3.8 cm obtained with the Huawei Y5 Smartphone camera. This method will be particularly interesting when simplicity, portability, and autonomy are desirable. In the future, it would be transposable to participatory science programs, while using an open RTK GNSS network.
Journal Article
Potential of Smartphone SfM Photogrammetry to Measure Coastal Morphodynamics
by
Bertin, Stéphane
,
Kervot, Matthieu
,
Delacourt, Christophe
in
Accuracy
,
Astronomical models
,
Beaches
2019
With recent advances in photogrammetric processing methods and sensor technologies, smartphones represent a new opportunity of mainstream, low-cost sensor, with a great potential for Structure-from-Motion (SfM) photogrammetry, and in particular for participatory science programs or citizen observatories. Keeping in mind the application in citizen observatories, three smartphone models (Galaxy S7®, Lumia 930® and iPhone 8®) and a bridge camera were compared (separately and in combination) for coastal applications: A coastal cliff and a sandy beach. Various acquisition protocols, at different distances from a cliff face and using “linear” or “fan-shaped” capture mode, were also assessed in their efficiency. A simultaneous Terrestrial Laser Scanner (TLS) survey provided a reference dataset to assess the quality of the SfM reconstructions. Satisfactory reconstructions (mean error < 5 cm) of the cliff face were obtained using all smartphone models tested. To measure the cliff face, fan-shaped capturing mode allowed a quicker image acquisition on site and better results (mean error of 1.3 cm with a standard deviation of 0.1 cm at 20 m from the cliff face) than linear capturing mode (mean error of 2.5 cm with a standard deviation of 21.8 cm), provided that the distance to the cliff face is sufficient to ensure a good image overlap. To obtain satisfactory results over beaches, we show that it is preferable to have high-angle shots of the study area, which may limit the applicability of the method for certain sites.
Journal Article
Assessment of RTK Quadcopter and Structure-from-Motion Photogrammetry for Fine-Scale Monitoring of Coastal Topographic Complexity
2022
Advances in image-based remote sensing using unmanned aerial vehicles (UAV) and structure-from-motion (SfM) photogrammetry continue to improve our ability to monitor complex landforms over representative spatial and temporal scales. As with other water-worked environments, coastal sediments respond to shaping processes through the formation of multi-scale topographic roughness. Although this topographic complexity can be an important marker of hydrodynamic forces and sediment transport, it is seldom characterized in typical beach surveys due to environmental and technical constraints. In this study, we explore the feasibility of using SfM photogrammetry augmented with an RTK quadcopter for monitoring the coastal topographic complexity at the beach-scale in a macrotidal environment. The method had to respond to resolution and time constraints for a realistic representation of the topo-morphological features from submeter dimensions and survey completion in two hours around low tide to fully cover the intertidal zone. Different tests were performed at two coastal field sites with varied dimensions and morphologies to assess the photogrammetric performance and eventual means for optimization. Our results show that, with precise image positioning, the addition of a single ground control point (GCP) enabled a global precision (RMSE) equivalent to that of traditional GCP-based photogrammetry using numerous and well-distributed GCPs. The optimal model quality that minimized vertical bias and random errors was achieved from 5 GCPs, with a two-fold reduction in RMSE. The image resolution for tie point detection was found to be an important control on the measurement quality, with the best results obtained using images at their original scale. Using these findings enabled designing an efficient and effective workflow for monitoring coastal topographic complexity at a large scale.
Journal Article
Correction of Refraction Effects on Unmanned Aerial Vehicle Structure-from-Motion Bathymetric Survey for Coral Reef Roughness Characterisation
2025
Coral reefs play a crucial role in tropical coastal ecosystems, even though these environments are difficult to monitor due to their diversity and morphological complexity and due to their shallowness in some cases. This study used two approaches for acquiring very-high-resolution bathymetric data: underwater structure-from-motion (SfM) photogrammetry collected from a low-cost platform and unmanned/uncrewed aerial vehicle (UAV)-based SfM photogrammetry. While underwater photogrammetry avoids the distortions caused by refraction at air/water interface, it remains limited in spatial coverage (about 0.04 ha in 1 h of survey). In contrast, UAV photogrammetry allows for covering extensive areas (more than 20 ha/h) but requires applying refraction correction in order to accurately compute bathymetry and roughness values. An analytical approach based on Snell laws and an empirical approach based on linear regression (calibrated using a batch of points whose depths are representative of the depth range of the surveyed areas) are tested to correct the apparent depth on the raw UAV digital elevation model (DEM). Comparison to underwater photogrammetry shows that correcting refraction reduces the root mean square error (RMSE) by more than 50% (up to 62%) on bathymetric models, with RMSE lower than 0.13 m for the analytical approach and down to 0.09 m for the regression method. The linear-regression-based refraction correction proved most effective in restoring accurate seabed roughness, with a mean error on roughness lower than 17% (vs. 30% for analytical refraction correction and 48% for apparent bathymetry).
Journal Article
CYP450 Genotype—Phenotype Concordance Using the Geneva Micrococktail in a Clinical Setting
by
Bertin, Stéphane
,
Samer, Caroline F.
,
Rollason, Victoria
in
Analgesics
,
Antidepressants
,
Caffeine
2021
Pharmacokinetic variability is a major source of differences in drug response and can be due to genetic variants and/or drug-drug interactions. Cytochromes P450 are among the most studied enzymes from a pharmacokinetic point of view. Their activity can be measured by phenotyping, and/or predicted by genotyping. Depending on the presence of drugs and/or diseases that can affect their in vivo activity, both approaches can be complementary. In 2014, the Geneva cocktail using dried blood spots was validated in healthy volunteers for CYP450 phenotyping. Since its clinical implementation, it has been used in approximately 500 patients in various clinical situations. Our study aims to report the concordance between CYP450 genotype and phenotype in real-life patients. The prospectively collected data from patients who were genotyped and/or phenotyped between January 2014 and December 2020 were reviewed. A total of 537 patients were genotyped and/or phenotyped for CYP450 during this period, and 241 underwent simultaneous genotyping and phenotyping allowing for genotype/phenotype concordance assessment. Genotyping correctly predicted poor metabolizer phenotypes for most CYPs isoenzymes studied, whereas agreement was more variable for intermediate, normal, and ultrarapid metabolizers. Discrepancies between the phenotype predicted on the basis of genotyping and the measured phenotype were not always explained by concurrent medication (phenotypic switch). Therefore genotyping and phenotyping tests are complementary approaches when aiming to individualize drug therapy. In the 537 patients, the majority of clinical situations were observed with analgesic/anesthetic drugs ( n = 187), followed by antidepressants ( n = 153), antineoplastics ( n = 97), and immunosuppressants ( n = 93). Inefficacy (or low drug levels) and adverse drug reaction (or high drug levels) were the main reasons for testing. Genotype and/or phenotype results explained or at least contributed to the clinical event in 44% of cases.
Journal Article
Effects of Extracorporeal Membrane Oxygenation Circuits on Drug Sequestration: A Review of Ex Vivo Experiments
by
Bertin, Stéphane
,
Di Paolo, Ermindo R.
,
Perez, Maria-Helena
in
Biocompatibility
,
Caspofungin
,
Circuits
2025
Background: Extracorporeal membrane oxygenation (ECMO) can affect the disposition of drugs, notably by sequestering them in a circuit. This review aimed to provide a comprehensive summary of existing ex vivo studies investigating the impact of contemporary ECMO circuits on drug sequestration, and to examine the associations between the physicochemical properties of drugs, the features and settings of ECMO devices, and the extent of drug sequestration. Method: A comprehensive search was conducted to identify ex vivo studies that determined drug concentrations in ECMO circuits. Studies that did not allow for the proper assessment of drug loss by degradation were excluded. Drug characteristics and experimental conditions were recorded. Drug sequestration in the circuit was calculated as the difference between the drug loss measured in the ECMO circuit and the drug loss due to spontaneous degradation measured under control conditions. To identify predictors of drug sequestration, a stepwise multiple linear meta-regression was applied by testing the physicochemical properties of drugs and ECMO device features/settings. Results: A total of 40 studies were identified, of which 21 were included in the analysis, covering 41 drugs. The Maquet membrane oxygenator was the most used brand (73%). About half of the circuits were adult and half were pediatric. Our final regression model retained lipophilicity, and to a lesser extent ionization at a physiological pH, as significant predictors of drug sequestration (R2 0.44, relative standard error 23%). Protein binding had no additional effect. Anti-infectives were the most studied class of drugs (n = 28). Antibiotics were overall not significantly sequestered, while lipophilic drugs such as posaconazole, voriconazole, paracetamol, fentanyl, sufentanil, propofol, thiopental, dexmedetomidine and amiodarone were highly sequestered (≥50%). However, this sequestration occurred mainly within the first few hours of the experiments, possibly reflecting a saturation effect. Conclusions: Lipophilic drugs are significantly sequestered in ex vivo ECMO circuits, although this effect may be limited by early saturation.
Journal Article
Surface proteins involved in the adhesion of Streptococcus salivarius to human intestinal epithelial cells
2018
The adhesion properties of 14 Streptococcus salivarius strains to mucus (HT29-MTX) and non-mucus secreting (Caco-2/TC7) human intestinal epithelial cells were investigated. Ability to adhere to these two eukaryotic cell lines greatly differs between strains. The presence of mucus played a major factor in adhesion, likely due to high adhesiveness to mucins present in the native human mucus layer covering the whole cell surface. Only one S. salivarius strain (F6-1), isolated from the feces of a healthy baby, was found to strongly adhere to HT-29 MTX cells at a level comparable to that of Lactobacillus rhamnosus GG, a probiotic strain considered to be highly adherent. By sequencing the genome of F6-1, we were able to identify 36 genes encoding putative surface proteins. Deletion mutants were constructed for six of them and their adhesion abilities on HT-29 MTX cells were checked. Our study confirmed that four of these genes encode adhesins involved in the adhesion of S. salivarius to host cells. Such adhesins were also identified in other S. salivarius strains.
Journal Article
Grain and bedform roughness properties isolated from gravel-patch DEMs
by
Friedrich, Heide
,
Bertin, Stephane
,
Groom, Jane
in
Autocorrelation functions
,
Bedforms
,
Digital Elevation Models
2018
Remote sensing of gravel-bed patches and resulting high-resolution digital elevation models (DEMs) allow for the identification of various spatial scales of surface roughness. Thus far, dimensions relating to grain and bedform roughness scales have been determined using semivariograms or equivalent structure/autocorrelation functions. However, it is difficult to clearly differentiate roughness scales and separate analysis of roughness properties is not possible. This study examines the use of moving-window detrending on gravel-patch DEMs for isolating grain and bedform roughness and their respective topographic signatures. An extensive dataset of water-worked gravel surfaces collected in both laboratory and field environments is used. The measured bed topography is separated into two distinct DEMs: one representing grains, the other representing bedforms, and roughness properties are determined separately for grain and bedform DEMs. The results show that both roughness scales are controlled by the size of the coarse sediment forming the bed surface, with positive linear relationships connecting bed composition and vertical roughness. Coarse sediment is controlling bedform development by forming humps on the surface, in the lee of which finer sediment is sheltered. We present synthesis relationships connecting vertical roughness of gravel patches to the vertical roughness of grains and bedforms.
Journal Article
A long-term dataset of topography and nearshore bathymetry at the macrotidal pocket beach of Porsmilin, France
by
Deschamps, Anne
,
Prunier, Christophe
,
Belleney, Déborah
in
704/2151/210
,
704/2151/215
,
704/2151/2809
2022
Long-term datasets documenting the evolution of coastal forms and processes, through the provision of recurring beach as well as shoreface morphological observations and accompanying time-series of environmental controls, remain difficult to collect and are rarely made available. However, they are increasingly needed to further our understanding of coastal change and to improve the models that will help planning what our future coast will be. This data descriptor presents the results of topographic and bathymetric surveys at Porsmilin, a macrotidal embayed beach situated in Brittany, northwest France. The Porsmilin beach survey program was launched in January 2003 by the Institut Universitaire Européen de la Mer (IUEM/Univ. Brest) and is continuing today in the framework of the French coastal observation service SNO-DYNALIT. The dataset contains over 16 years of monthly beach profile surveys and a large collection of repeated high-resolution subtidal and subaerial digital elevation models (DEMs). The dataset is accompanied by time-series of inshore waves and water levels, and enriched metadata, that will facilitate its future reuse in coastal research.
Measurement(s)
Beach topography • Nearshore bathymetry
Technology Type(s)
RTK-GNSS • Terrestrial laser scanning • Digital photogrammetry • Multibeam echosounder
Factor Type(s)
Elevation
Sample Characteristic - Environment
shore
Sample Characteristic - Location
Bretagne Region
Journal Article
Analysis of Streptococcus agalactiae pan-genome for prevalence, diversity and functionality of integrative and conjugative or mobilizable elements integrated in the tRNALys CTT gene
by
Bertin, Stéphane
,
Guédon, Gérard
,
Payot, Sophie
in
Animal Genetics and Genomics
,
antibiotic resistance
,
Biochemistry
2015
Streptococcus agalactiae is the first cause of invasive infections in human neonates and is also a major bovine and fish pathogen. High genomic diversity was observed in this species that hosts numerous mobile genetic elements, in particular elements transferable by conjugation. This works aims to evaluate the contribution of these elements to GBS genome diversity. Focusing on genomic islands integrated in the tRNA(Lys) (CTT) gene, a known hotspot of recombination, an extensive in silico search was performed on the sequenced genome of 303 strains of S. agalactiae isolated from different hosts. In all the isolates (except 9), whatever their origin (human, bovine, camel, dog, gray seal, dolphin, fish species or bullfrog), this locus carries highly diverse genomic islands transferable by conjugation such as integrative and conjugative elements (ICEs), integrative and mobilizable elements (IMEs), CIs-mobilizable elements (CIMEs) or composite elements. Transfer of an ICE from an ST67 bovine strain to a phylogenetically distant ST23 human isolate was obtained experimentally indicating that there was no barrier to ICE transfer between strains from different hosts. Interestingly, a novel family of putative IMEs that site-specifically integrate in the nic site of oriT of ICEs belonging to Tn916/ICESt3 superfamily was detected in silico. These elements carry an antibiotic resistance gene (lsa(C)) already described to confer cross-resistance to lincosamides, streptogramins A and pleuromutilins. Further work is needed to evaluate the impact of these IMEs on the transfer of targeted ICEs and the mobility and the dissemination of these IMEs.
Journal Article