Towards common file formats and data standards for seafloor geodesy - Community Whitepaper for UNAVCO’s “Future Directions for Seafloor Geodesy” Committee, September 2020 (revision of July 13, 2021)

Seafloor geodesy experiments have been expanding considerably in recent years. More and more research teamsaround the globe are conducting projects to monitor the tectonic or volcanic deformation of the seafloor. Theseexperiments are commonly based on limited-duration experiments, but increasingly, permanent observatories arealso being installed. This dynamic development is very encouraging for the establishment of a strong community which arguably willlead to the emergence of a worldwide scientific and technical synergy. However, data andknowledge transferbetween the different groups working on similar topics are still limited at the present time. This can be partlyexplained by the fact that the instruments, infrastructure, and processing software developed are custom-made andthus various file formats are used, although the fundamental observables are most of the time identical. One wayto overcome this limitation is to set up exchange standards in the form of standardized file formats. These fileswould gather and store all the physical quantities observed and will prove useful for the processing simplificationand, in the end, the extraction of the geodetic signal sought. Furthermore, uniformized formats would allow muchmore easily the comparison of software and processing methods between research groups, whether during tests oroperational measurement campaigns. Standardized data will eventually provide a base for the activities of potentialfuture national or international observation services. They would also make it possible to envisage the datadissemination similar to geodetic data recorded on land

Nouméa: a new multi-mission calibration and validation site for past and future altimetry missions?

Today, monitoring the evolution of sea level in coastal areas is of importance, since almost 11 % of the world's population lives in low-lying areas. Reducing uncertainties in sea level estimates requires a better understanding of both altimetry measurements and local sea level dynamics. In New Caledonia, the Nouméa lagoon is an example of this challenge, as altimetry, coastal tide gauge, and vertical land motions from global navigation satellite systems (GNSSs) do not provide consistent information. The GEOCEAN-NC 2019 field campaign addresses this issue with deployments of in situ instruments in the lagoon (GNSS buoy, pressure gauge, etc.), with a particular focus on the crossover of one Jason-series track and two Sentinel-3A missions tracks. In this study, we propose a method to virtually transfer the Nouméa tide gauge at the altimetry crossover point, using in situ data from the field campaign. Following the philosophy of calibration and validation (Cal/Val) studies, we derive absolute altimeter bias time series over the entire Jason and Sentinel-3A periods. Overall, our estimated altimeter mean biases are slightly larger by 1–2 cm compared to Corsica and Bass Strait results, with inter-mission biases in line with those of Bass Strait site. Uncertainties still remain regarding the determination of our vertical datum, only constrained by the three days of the GNSS buoy deployment. With our method, we are able to re-analyse about 20 years of altimetry observations and derive a linear trend of −0.2 ± 0.1 mm yr−1 over the bias time series. Compared to previous studies, we do not find any significant uplift in the area, which is more consistent with the observations of inland permanent GNSS stations. These results support the idea of developing Cal/Val activities in the lagoon, which is already the subject of several experiments for the scientific calibration phase of the SWOT wide-swath altimetry mission.</p

Spectroscopie de pertes d'énergie d'électrons. Application a l'étude de la chimisorption de l'oxygène sur la face (100) du molybdène

We describe results of a study of the adsorption of oxygen on the (100) molybdenum face by électron energy loss spectroscopy. New transitions appear which confirm the values obtained by photoemission from the same system. The comparison between the two techniques is extended to other metal-adsorbed gas systems and there is a fair agreement.Les résultats d'une étude de l'adsorption d'oxygène sur la face (100) du molybdène par spectroscopie de pertes d'énergie d'électrons sont décrits. De nouvelles transitions apparaissent confirmant les valeurs obtenues par photoémission sur le même système. La comparaison des deux techniques est étendue à d'autres couples métal-gaz adsorbé et montre la bonne concordance des résultats

Geometrical reliability of overconstrained mechanisms with gaps

Reliability design relates generally to simulation of fatigue strength, thermal effects, etc. not to simulation of geometrical variations, i.e. tolerancing. The variables for geometrical reliability are manufacturing, gap and functional deviations. In case of isoconstrained mechanisms, the linear expression of dependencies between these variables allows to calculate failure probability. For overconstrained mechanisms, these linear expressions are not applicable for the whole behaviour of the mechanism; nevertheless, they are applicable for each particular configuration of contacts. The different configurations represent events taken into account in a numerical evaluation assumed by the Form–Sorm method. A case study, with numerical results, illustrates and validates the chosen process

Typology of geometrical defects in Electron Beam Melting

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Present‐day subsidence in the Ganges‐Brahmaputra‐Meghna Delta: eastern amplification of the Holocene sediment loading contribution

International audienceThe subsidence of the Ganges-Brahmaputra-Meghna Delta (GBMD) drastically increases the adverse impacts of coastal flooding and exacerbates the vulnerability of populations from ongoing rapid sea level rise. We focus here on estimating the present-day subsidence rates induced by the loading of sediments continuously deposited within the GBMD over the past 11,000 years. By constructing a realistic GBMD 3-D numerical model with laterally variable mantle and lithospheric structure, we demonstrate for the first time that the presence of the strong Indian Craton and the weakened Indo-Burma margin results in significant amplification of subsidence driven by sediment loading in the eastern part of the delta, where the population density is the highest (>1,000 habitants per km 2). Although uncertainties remain regarding the amplitude of subsidence, the rate estimates (2-3 mm/year) are found to be comparable to the present-day global mean sea level rise

Contributions of a Strengthened Early Holocene Monsoon and Sediment Loading to Present-Day Subsidence of the Ganges-Brahmaputra Delta

International audienceThe contribution of subsidence to relative sea level rise in the Ganges‐Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal Basin populations to sea level rise and storm surges. This paper focuses on estimating the present‐day subsidence induced by Holocene sediment in the Bengal Basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present‐day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present‐day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the twentieth century global mean sea level rise (1.1–1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations

Contributions of a strengthened early Holocene monsoon and sediment loading to present-day subsidence of the Ganges-Brahmaputra Delta

The contribution of subsidence to relative sea-level rise in the Ganges-Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal basin populations to sea level rise and storm surges. This paper focuses on estimating the present-day subsidence induced by Holocene sediment in the Bengal basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in-situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present-day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present-day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the 20th century global mean sea level rise (1.1-1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations