Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs.     

DEPTH-AVERAGED 2-D CALCULATION OF TIDAL FLOW,SALINITY AND COHESIVE SEDIMENT TRANSPORT IN ESTUARIES

A depth-averaged 2-D numerical model for unsteady flow, salinity and cohesive sediment transport in estuaries is established using the finite volume method on the non-staggered, curvilinear grid. The convection terms are discretized by upwind schemes, the diffusion terms are by the central difference scheme, and the time derivative terms are by the three-time-level implicit scheme. The coupling of flow velocity and water level in the 2-D shallow water equations is achieved by the SIMPLEC algorithm with the Rhie and Chow's momentum interpolation method. The sediment model calculates the settling, deposition, erosion and transport of cohesive sediment, taking into account the influence of sediment size, sediment concentration, salinity and turbulence intensity on the flocculation of cohesive sediment. The flow model is first tested against the measurement data in the Tokyo Bay and San Francisco Bay, showing good agreements. And then, the entire model of flow, salinity and sediment transport is verified in the Gironde Estuary. The water elevation, flow velocity, salinity and sediment concentration are well predicted.     

Estimation of hydrodynamic coefficients for flow around cylinders in side-by-side arrangement with variation in separation gap

A finite-volume method (FVM) using a multi-block grid technique has been applied to investigate the hydrodynamic coefficients and to categorize the two-dimensional flow pattern around a pair of adjacent cylinders (known here after as double cylinders). Matching grids were used at the interface between blocks (cylinders), and the boundary conditions are imposed around the periphery to exchange physical values across the interface. To validate the developed numerical method, a case with laminar viscous flow around a single cylinder was carried out, the results showed good agreement compared to previously published data. Hydrodynamic coefficients, Strouhal number, and stagnation point change were thoroughly investigated as a function of the separation between the two cylinders. It is found that the changes of hydrodynamic coefficients due to variations in separation are well characterized by the five different vortex flow patterns, which can also be used to explain the flow and vortex pattern around the double cylinders.     

COMPUTATIONAL SIMULATION OF RIVER SEDIMENTATION AND MORPHOLOGY - A REVIEW OF THE STATE OF THE ART

In this paper, the state-of-the-art computational simulation technologies for river sedimentation and morphology are comprehensively reviewed. Emphasis is on computational modelling, which includes mathematical modelling equations and closures, numerical solution methods, verification and validation, model integration, and applications. Several important areas of future research are recommended.     

Machine learning innovations in address matching: A practical comparison of word2vec and CRFs

Record linkage is a frequent obstacle to unlocking the benefits of integrated (spatial) data sources. In the absence of unique identifiers to directly join records, practitioners often rely on text‐based approaches for resolving candidate pairs of records to a match. In geographic information science, spatial record linkage is a form of geocoding that pertains to the resolution of text‐based linkage between pairs of addresses into matches and non‐matches. These approaches link text‐based address sequences, integrating sources of data that would otherwise remain in isolation. While recent innovations in machine learning have been introduced in the wider record linkage literature, there is significant potential to apply machine learning to the address matching sub‐field of geographic information science. As a response, this paper introduces two recent developments in text‐based machine learning—conditional random fields and word2vec—that have not been applied to address matching, evaluating their comparative strengths and drawbacks.     

A high speed photometer in the optical region for lunar occultation studies

High speed photometry during the lunar occultation of a stellar system provides an effective means of achieving high angular resolution in one dimension at the sub arc second level which is well suited for resolving close binary projected separations in the range of 10–100 milliarc seconds. An optical fast photometer designed for such a purpose is described and some results from the initial observations taken with the system including the resolution of a projected separation of 55 milli arcsecond in one binary system are detailed.     

Quantitative interrogation of a fossilized carbonate sand body – The Pleistocene Miami oolite of South Florida

Exposures of the Pleistocene Miami oolite in South Florida provide excellent examples of preserved primary sedimentary features and subsequent diagenetic changes of a ‘fossilized’ ooid sand body that has been subaerially exposed in a tropical climate since its deposition during the last interglacial highstand – Marine Isotope Stage 5e. Using a robust airborne light detection and ranging digital terrain model and select outcrops, a detailed analysis of the morphologies and dimensions of the different portions of the Miami oolite was conducted. The sand body, extending 95 km north to south and approximately 15 km wide, consists of shoals (or bars) separated by tidal channels and is partly bounded on the ocean‐facing side by a prograding barrier bar that collectively cover an area of approximately 1000 sq. km. Results of the quantitative interrogation of the Miami oolite are compared with those of previously published work from modern sand bodies on Great Bahama Bank including the Exumas, Schooners Cays and Tongue of the Ocean. Digital terrain models developed for these modern sand bodies on the Great Bahama Bank and the ancient Miami oolite were used as the basis for the definition of shoals, shoal crests (peaks) and channels which were examined with respect to their size, shape and orientation. The Exumas sand body is the best morphometric match when analysing the bars and the channels, and the Joulter Cays area is an analogue for the formation of the barrier bar and for burrow reworking of cross‐bedding within stabilized sand shoals. The Exumas is a particularly compelling analogue for the Miami oolite with respect to length and overall visual comparison between the morphologies of the sand bodies, shoal (or bar) shape, number of tidal channels, channel length and width, and high areas parallel to the strike trend of the sand body (islands in the Exumas and possible islands as part of the Miami oolite barrier bar). Despite ca 115 kyr of subaerial exposure and meteoric diagenesis including karst, the morphology of the Miami oolite is still relatively intact to the point where it can be easily analysed and meaningful comparisons to modern systems can be made. The Miami oolite serves as a key reference example for comparison to Holocene sand units in the Bahamas – it validates the concept of comparative sedimentology and in particular emphasizes how results from the modern can improve the interpretation of a fossilized example.     

The role of “excess” CO2 in the formation of trona deposits

The prevailing theory for the formation of trona [Na₃(CO₃)(HCO₃) · 2(H₂O)] relies on evaporative concentration of water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments. Given the abundance of closed drainage basins dominated by volcanics, it is puzzling that there are so few trona deposits and present-day lakes that would yield dominantly Na–CO₃ minerals upon evaporation. Groundwater in the San Bernardino Basin (southeastern Arizona, USA and northeastern Sonora, Mexico) would yield mainly Na–CO₃ minerals upon evaporation, but waters in the surrounding basins would not. Analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology, but the injection of magmatic CO₂. Many major deposits of trona and Na–CO₃-type lakes appear to have had “excess” CO₂ input, either from magmatic sources or from the decay of organic matter. It is proposed that, along with the presence of volcanics, addition of “excess” CO₂ is an important pre-condition for the formation of trona deposits.     

Multivariate analysis of sedimentary environments using grain-size frequency distributions

Multivariate statistics were used to characterize and test the effectiveness of grain-size frequencies as environmental discriminators. Sediment from the following two depositional systems along eastern Lake Michigan were studied: (1) a closed system with respect to available grain sizes (Little Sable Point), and (2) an open system (Sleeping Bear Point-Manitou Passage). Principal components analysis shows that grain-size distributions are composed of two or more subgroups that reflect surface creep bedload, mixed suspension bedload, and uniform suspension. Discriminant function and principal latent vector analyses of the Little Sable Point environments show that, when available sediment is limited with respect to grain size (0.5 φto 3.0 φ), similar size distributions can occur in environments supposedly characterized by different energy conditions. Sediment in the Sleeping Bear Point-Manitou Passage system is not restricted to available grain sizes and the environments discriminated very well (α < 0.001). The grain-size distributions are such that they reflect differences in energy conditions within the environments. It is apparent that the grain sizes available to a depositional system control to a great extent the effectiveness of environmental discrimination.