Enhancing subtle seafloor relief variation: relief visualisation techniques for bathymetric data 

2021 ◽  
Author(s):  
Ana Novak ◽  
Sašo Poglajen ◽  
Marko Vrabec
Keyword(s):  
Small Scale ◽  
View Factor ◽  
M Cell ◽  
Northern Adriatic ◽  
Bathymetric Data ◽  
Continental Shelves ◽  
Digital Elevation ◽  
Local Relief ◽  
Oriented Parallel ◽  
Local Dominance

<p>Bathymetric data is commonly visualized as a simple shaded relief, where features oriented parallel to the light source are prone to false topographic perception or are even obscured to the viewer. On the other hand, many relief visualisation techniques developed in past decades are extensively used in visualisation and analysis of high-resolution digital elevation models, especially in geomorphological and archaeological studies. We tested and assessed the suitability of relief visualisation techniques provided by the Relief Visualisation Toolbox (RVT) software for representation of bathymetric data. We used a multibeam-sonar derived bathymetric model with a 10 x 10 m cell size from the Gulf of Trieste (northern Adriatic) characterised by a shallow low-relief seabed. Our results clearly demonstrate the effectiveness of relief visualisation techniques for exposing subtle relief variation in bathymetric data. We find that small-scale features (outcrops, wrecks, pockmarks, reefs, etc.) and negative linear features are best highlighted by “visualization for archaeological topography” (VAT) and “openness” techniques. High-relief features and topographic infection points are pronounced by “hillshade from multiple directions” and “sky-view factor” (SVF). Finally, “principal components analysis” (PCA), “prismatic openness”, “simple local relief model”, “anisotropic SVF” and “local dominance” algorithms show best results when we want to highlight both high- and low-relief features in one image. The tested techniques are far superior to a simple hillshade visualisation especially when imaging low-gradient relief (common on continental shelves and abyssal plains) where topographic details are often not adequately pronounced by hillshading. To our knowledge, this study represents the first attempt to test and compare several relief visualisation techniques for bathymetric data.  </p>

scholarly journals Self-AdaptIve LOcal Relief Enhancer (SAILORE): A New Filter to Improve Local Relief Model Performances According to Local Topography

Geomatics ◽  
2021 ◽  
Vol 1 (4) ◽  
pp. 450-463
Author(s):  
Jean-Pierre TOUMAZET ◽  
François-Xavier SIMON ◽  
Alfredo MAYORAL
Keyword(s):  
Low Frequency ◽  
View Factor ◽  
Digital Elevation ◽  
Local Relief ◽  
Optimal Values ◽  
Elevation Model ◽  
Filtering Effect ◽  
Steep Slopes ◽  
Natural Slopes ◽  
Self Adaptive

The use of Light Detection and Ranging (LiDAR) is becoming more and more common in different landscape exploration domains such as archaeology or geomorphology. In order to allow the detection of features of interest, visualization filters have to be applied to the raw Digital Elevation Model (DEM), to enhance small relief variations. Several filters have been proposed for this purpose, such as Sky View Factor, Slope, negative and positive Openness, or Local Relief Model (LRM). The efficiency of each of these methods is strongly dependent on the input parameters chosen in regard of the topography of the investigated area. The LRM has proved to be one of the most efficient, but it has to be parameterized in order to be adapted to the natural slopes characterizing the investigated area. Generally, this setting has a single value, chosen as the best compromise between optimal values for each relief configuration. As LiDAR is mainly used in wide areas, a large distribution of natural slopes is often encountered. The aim of this paper is to propose a Self AdaptIve LOcal Relief Enhancer (SAILORE) based on the Local Relief Model approach. The filtering effect is adapted to the local slope, allowing the detection at the same time of low-frequency relief variation on flat areas, as well as the identification of high-frequency relief variation in the presence of steep slopes. First, the interest of this self-adaptive approach is presented, and the principle of the method, compared to the classical LRM method, is described. This new tool is then applied to a LiDAR dataset characterized by various terrain configurations in order to test its performance and compare it with the classical LRM. The results of this test show that SAILORE significantly increases the detection capability while simplifying it.

scholarly journals Short-term post-mortality scavenging and longer term recovery after anoxia in the northern Adriatic Sea

2013 ◽  
Vol 10 (11) ◽  
pp. 7647-7659 ◽  
Author(s):  
M. Blasnig ◽  
B. Riedel ◽  
L. Schiemer ◽  
M. Zuschin ◽  
M. Stachowitsch
Keyword(s):  
Adriatic Sea ◽  
Time Lapse ◽  
Hermit Crabs ◽  
Small Scale ◽  
Short Term ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Hexaplex Trunculus ◽  
Distinct Sequence ◽  
And Function

Abstract. The northern Adriatic Sea is one of nearly 500 areas worldwide suffering widespread mortalities due to anoxia. The present study documents post-anoxia macrofauna dynamics after experimentally inducing small-scale anoxia in 24 m depth (2 plots, each 50 cm × 50 cm). Time-lapse camera deployments examined short-term scavenging of the moribund and dead organisms (multi-species clumps consisting of sponges and ascidians) over two 3-day periods (August 2009: 71.5 h, September 2009: 67.5 h). Longer term recovery (days to 2 yr) in the same two plots was examined with an independent photo series. Scavengers arrived quickly and in a distinct sequence: demersal (Gobius niger, Serranus hepatus) and benthopelagic fishes (Diplodus vulgaris, Pagellus erythrinus), followed by hermit crabs (Paguristes eremita, showing a clear day/night rhythm in presence) and gastropods (Hexaplex trunculus). This sequence is attributed to the relative speeds and densities of the organisms. The sessile fauna was largely removed or consumed within seven (August plot) and 13 (September plot) days after anoxia, confirming our first hypothesis that decaying organisms are quickly utilised. The scavengers remained in dense aggregations (e.g. up to 33 P. eremita individuals at one time) as long as dead organisms were available. No recovery of sessile macroepibenthos macroepibenthos occurred in the experimental plots one and two years after anoxia, undermining our second hypothesis that small denuded areas are more rapidly recolonised. This study underlines the sensitivity of this soft-bottom community and supports calls for reducing additional anthropogenic disturbances such as fishing practices that further impede recolonisation and threaten benthic community structure and function over the long term.

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored ADCP

2019 ◽  
Author(s):  
Rob Hall ◽  
Barbara Berx ◽  
Gillian Damerell
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Low Frequency ◽  
Internal Tide ◽  
Small Scale ◽  
Potential Density ◽  
The North ◽  
Model Study ◽  
Continental Shelves ◽  
Alternative Approach

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide, to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring-neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being fished-out by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimise these risks, with u measured by a low-frequency ADCP moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the M2 internal tide radiating from the Wyville Thompson Ridge in the North Atlantic. The observed energy flux (4.2 ± 0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by sub-sampling potential density in an idealised internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

scholarly journals Predicting Channel Conveyance and Characterizing Planform Using River Bathymetry via Satellite Image Compilation (RiBaSIC) Algorithm for DEM-Based Hydrodynamic Modeling

2020 ◽  
Vol 12 (17) ◽  
pp. 2799
Author(s):  
Md N M Bhuyian ◽  
Alfred Kalyanapu
Keyword(s):  
Mean Squared Error ◽  
Satellite Image ◽  
Shuttle Radar Topography Mission ◽  
Willamette River ◽  
Bathymetric Data ◽  
Digital Elevation ◽  
Channel Slope ◽  
Dem Accuracy ◽  
Landsat Satellite ◽  
Discharge Estimation

Digital Elevation Models (DEMs) are widely used as a proxy for bathymetric data and several studies have attempted to improve DEM accuracy for hydrodynamic (HD) modeling. Most of these studies attempted to quantitatively improve estimates of channel conveyance (assuming a non-braided morphology) rather than accounting for the actual channel planform. Accurate representation of river conveyance and planform in a DEM is critical to HD modeling and can be achieved with a combination of remote sensing (e.g., satellite image) and field data, such as water surface elevation (WSE). Therefore, the objectives of this study are (i) to develop an algorithm for predicting channel conveyance and characterizing planform via satellite images and in situ WSE and (ii) to estimate discharge using the predicted conveyance via an HD model. The algorithm is named River Bathymetry via Satellite Image Compilation (RiBaSIC) and uses Landsat satellite imagery, Shuttle Radar Topography Mission (SRTM) DEM, Multi-Error-Removed Improved-Terrain (MERIT) DEM, and observed WSE. The algorithm is tested on four study areas along the Willamette River, Kushiyara River, Jamuna River, and Solimoes River. Channel slope and predicted hydraulic radius are subsequently estimated for approximating Manning’s roughness factor. Two-dimensional HD models using DEMs modified by the RiBaSIC algorithm and corresponding Manning’s roughness factors are employed for discharge estimation. The proposed algorithm can represent river planform and conveyance in single-channeled, meandering, wandering, and braided river reaches. Additionally, the HD models estimated discharge within 14–19% relative root mean squared error (RRMSE) in simulation of five years period.

scholarly journals Ecological regime shift preserved in the Anthropocene stratigraphic record

2020 ◽  
Vol 287 (1929) ◽  
pp. 20200695 ◽  
Author(s):  
Adam Tomašových ◽  
Paolo G. Albano ◽  
Tomáš Fuksi ◽  
Ivo Gallmetzer ◽  
Alexandra Haselmair ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Fossil Record ◽  
Regime Shift ◽  
Benthic Communities ◽  
Ecological Change ◽  
Benthic Assemblages ◽  
Northern Adriatic ◽  
Ecological Release ◽  
Continental Shelves ◽  
Decadal Scale

Palaeoecological data are unique historical archives that extend back far beyond the last several decades of ecological observations. However, the fossil record of continental shelves has been perceived as too coarse (with centennial-millennial resolution) and incomplete to detect processes occurring at yearly or decadal scales relevant to ecology and conservation. Here, we show that the youngest (Anthropocene) fossil record on the northern Adriatic continental shelf provides decadal-scale resolution that accurately documents an abrupt ecological change affecting benthic communities during the twentieth century. The magnitude and the duration of the twentieth century shift in body size of the bivalve Corbula gibba is unprecedented given that regional populations of this species were dominated by small-size classes throughout the Holocene. The shift coincided with compositional changes in benthic assemblages, driven by an increase from approximately 25% to approximately 70% in median per-assemblage abundance of C. gibba . This regime shift increase occurred preferentially at sites that experienced at least one hypoxic event per decade in the twentieth century. Larger size and higher abundance of C. gibba probably reflect ecological release as it coincides with an increase in the frequency of seasonal hypoxia that triggered mass mortality of competitors and predators. Higher frequency of hypoxic events is coupled with a decline in the depth of intense sediment mixing by burrowing benthic organisms from several decimetres to less than 20 cm, significantly improving the stratigraphic resolution of the Anthropocene fossil record and making it possible to detect sub-centennial ecological changes on continental shelves.

scholarly journals Heterogeneidade da Rugosidade em Terrenos Complexos e Implicações para o Aproveitamento Eólico (Heterogeneity of Roughness in Complex Terrains and Implications for Wind Power)

2016 ◽  
Vol 9 (2) ◽  
pp. 546
Author(s):  
Thiago Lobão Cordeiro ◽  
Arcilan Trevenzoli Assireu ◽  
Ramon Moraes Freitas ◽  
Nandamudi Lankalapalli Vijaykumar ◽  
Reinaldo Roberto Rosa
Keyword(s):  
Wind Power ◽  
Roughness Length ◽  
Small Scale ◽  
Measuring Point ◽  
Wind Pattern ◽  
Displacement Height ◽  
Digital Elevation ◽  
Wind Profiles ◽  
Elevation Model ◽  
Plane Displacement

A demanda para a produção de energia renovável e de baixo impacto ambiental cresce a cada ano e, com isso, há também o aumento do interesse em turbinas eólicas de pequena escala a serem instaladas em relevos complexos que inclui áreas onde montanhas afetam o padrão de vento, como em grandes sistemas aquáticos localizados em regiões de planaltos. A influência da complexidade do relevo e da intensidade de turbulência foi investigada pela aplicação do método de Análise por Padrões de Gradientes em um modelo digital de elevação e uma série de dados histórica da direção e velocidade do vento. Os resultados indicaram que os padrões de fluxos são extremamente complexos e variam significativamente dependendo da direção do fluxo em sentido contrário. Esta variabilidade também torna difícil definir um plano zero de deslocamento ou um comprimento de rugosidade para um determinado ponto de medição, o que compromete a utilização do modelo de extrapolação vertical do vento baseado no coeficiente de rugosidade fixo.      ABSTRACT As the demand for environmentally friendly energy production grows, there is also an increased interest in small scale wind turbines located in more complex relief that includes areas where mountains affect the wind pattern, as in large inland aquatic system localized close to hills. Influence of complex relief on the turbulence intensity was investigated by means of time series of the wind direction and speed and digital elevation model. The results indicated that the flow patterns are highly complex and vary significantly depending on the direction of the oncoming flow. This variability also makes it difficult to define a general zero plane displacement height or a roughness length for a certain measuring point. The resulting consequence for the usual one-dimensional wind profiles models are then pointed out. Keywords: GPA. Roughness of the relief. Wind power.   

scholarly journals Application of the global SRTM and AW3D30 digital elevation models to mapping folds at cave sites

2021 ◽  
Vol 50 (1) ◽  
pp. 75-89
Author(s):  
Mark Abolins ◽  
Albert Ogden
Keyword(s):  
Cell Size ◽  
Forest Canopy ◽  
Digital Elevation Models ◽  
Digital Terrain Model ◽  
Surface Model ◽  
M Cell ◽  
Terrain Model ◽  
Digital Terrain ◽  
Digital Elevation ◽  
The Mean

A novel method to map and quantitatively describe very gentle folds (limb dip <5°) at cratonic cave sites was evaluated at Snail Shell and Nanna caves, central Tennessee, USA. Elevations from the global SRTM digital terrain model (DTM) were assigned to points on late Ordovician geologic contacts, and the elevations of the points were used to interpolate 28 m cell size natural neighbor digital elevation models (DEM’s) of the contacts. The global Forest Canopy Height Dataset was subtracted from the global 28 m cell size AW3D30 digital surface model (DSM) to create a DTM, and that DTM was applied in the same way. Comparison of mean and modal strikes of the interpolated surfaces with mean and modal cave passage trend shows that many passages are sub-parallel to the trend of an anticline. WithiSn 500 m of the caves, the SRTM- and AW3D30-based interpolated surfaces have mean strikes within 8° of the mean strike of an interpolated reference surface created with a high resolution (~0.76 m cell size and 10 cm RMSE) Tennessee, USA LiDAR DTM. This evaluation shows that the SRTM- and AW3D30-based method has the potential to reveal a relationship between the trend of a fold, on one hand, and cave passages, on the other, at sites where a geologic contact varies in elevation by >35 m within an area of <12.4 km2 and the mean dip of bedding is >0.9°.

scholarly journals A Modern Look at ‘Interstellar Clouds’

1974 ◽  
Vol 60 ◽  
pp. 13-44
Author(s):  
Carl Heiles
Keyword(s):  
Magnetic Field ◽  
Cloud Model ◽  
Scale Structure ◽  
Doppler Velocity ◽  
Small Scale ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Small Scale Structure ◽  
Oriented Parallel ◽  
Intercloud Medium

We compare past and present modes of investigation of the structure of the interstellar gas. Many aspects of the interstellar cloud model are invalid.Interstellar optical absorption lines and Hi21-cm emission lines show a number of very large aggregates with properties similar to those of ‘cloud complexes’. At nonzero velocities especially for b<0°, exist optical lines which have no Hicounterparts. These are almost certainly produced in low-density gas clouds; perhaps the intercloud medium is itself cloudy.Maps of Hicolumn density taken over large velocity ranges do not reveal much small-scale structure. This fact cannot easily be reconciled with the statistical analyses of interstellar reddening. The maps do reveal large, coherent gas structures which are often filamentary in shape and at least sometimes aligned parallel to the interstellar magnetic field.Maps of Hicolumn density over small velocity ranges show much small-scale structure, often filamentary in shape. The filaments are almost universally oriented parallel to the interstellar magnetic field and have Doppler velocity gradients along their lengths. In one area the geometry of the field and gas almost exclusively suggests Alfvén-type motions.

Prediction of soil salinity risk by digital terrain modeling in the Canadian prairies

2000 ◽  
Vol 80 (3) ◽  
pp. 455-463 ◽  
Author(s):  
I. V. Florinsky ◽  
R. G. Eilers ◽  
G. W. Lelyk
Keyword(s):  
Soil Salinity ◽  
Risk Index ◽  
Small Scale ◽  
Canadian Prairies ◽  
Digital Terrain ◽  
Terrain Models ◽  
Digital Elevation ◽  
Soil Salinisation ◽  
Elevation Model ◽  
Digital Terrain Modeling

Soil salinisation is a typical problem for the Canadian prairies. At macro-topographic scale, build-up of salts occurs in depressions. However, this relationship is not displayed on existing small-scale maps of soil salinity. To improve these maps, one can use a concept of accumulation, transition and dissipation zones of the landsurface. The concept allows one to reveal depressions (topographically expressed accumulation zones) using digital models of horizontal and vertical curvatures, or accumulation and mean curvatures derived from a digital elevation model. We applied the concept of accumulation, transition and dissipation zones to improve an existing small-scale map of the salinity risk index for the prairies and adjacent areas. A comparison of the old and the improved maps demonstrated that once data on depressions have been taken into account, areas marked by salinity risk decreased significantly. We suggest that the method used may prevent an overestimation in predictions of soil cover degradation due to salinisation. The method used can also reveal saline areas linked with discharges of saline aquifers. This is because sites marked by high discharges of groundwater usually relate to sites of intensive fracturing of geological materials, which are closely associated with topographically expressed accumulation zones. Key words: Digital terrain models, topography, soil salinisation, mapping

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