Littérature scientifique sur le sujet « Land Transition identification »

Regional land use transitions driven by the adaptive reconciliation of existing land use conflict with socioeconomic development can lead to positive economic effects as well as new land use conflict. Although research on land use transition has progressed considerably, limited studies have explored the spatiotemporal dynamic pattern of land use conflict during the land use transition period. Previous evaluation approaches on land use conflict that mainly focus on status or potential conflict lack conflict intensity evaluation during the land use transition process. A new spatially explicit evaluation framework of land use conflict that directly examines three aspects of conflict, namely, ecological and agricultural (EAC), agricultural and construction (ACC), and ecological and construction (ECC) land conflicts based on ecological quality and agricultural suitability, is proposed in this study. The spatiotemporal dynamic pattern and driving factors of land use conflict in the Yangtze River Economic Belt of China in the period of 2000–2018 are evaluated. The results indicated that comprehensive land use conflict (CLUC) intensity slightly decreased by 9.91% and its barycenter showed a trend toward the west during 2000–2018. ACC is the most drastic conflict among the three aspects of conflict. The mean intensity of ACC reduced remarkably by 38.26%, while EAC increased by 33.15% and ECC increased by 28.28% during the research periods. The barycenter of EAC moved toward the east while the barycenter of ACC and ECC moved toward the west. The changes in the intensity and spreading pattern of land use conflict indices demonstrated the changes in the pattern of territorial space development. Total population, population density, per capita GDP, number of mobile phone users, and road density were strong drivers that influenced the land use conflict of territorial space. Multiple policy recommendations including improving territorial space planning and governance ability, and improving land use efficiency, were proposed to manage and resolve the land use conflict of territorial space. The results and conclusions of this study will help improve future regional land use policies and reduce land use conflict.

Abstract Last decades of research have revealed the environmental impacts of Land-Use/Cover Change (LUCC) throughout the globe. Human activities’ impact is becoming more and more pronounced on the natural environment. The key activity in the LUCC projects has been to simulate the syntheses of knowledge of LUCC processes, and in particular to advance understanding of the causes of land-cover change. Still, there is a need of developing case studies regional models to understand LUCC change patterns. The aim of this work is to reveal and describe the main changes in LUCC patterns occurring in Poznań Lakeland Mesoregion according to CORINE Land Cover database. Change analysis was the basis for the identification of the main drivers in land cover changes in the study area. The dominant transitions that can be grouped and modelled separately were identified. Each submodel was combined with all submodels in the final change prediction process. Driver variables were used to model the historical change process. Transitions were modelled using multi-layer perceptron (MLP) method. Using the historical rates of change and the transition potential model scenario for year 2006 was predicted. Corine Land Cover 2006 database was used for model validation.

Land use conflicts are intensifying due to the rapid urbanization and accelerated transformation of social and economic development. Accurate identification of land use conflicts is an important prerequisite for resolving land use conflicts and optimizing the spatial pattern of land use. Previous studies on land use conflict using multi-objective evaluation methods mainly focused on the suitability or competitiveness of land use, ignoring land resource scarcity and the diversity of human needs, hence reducing the accuracy of land use conflict identification. This paper proposes a new framework for land use conflict identification. Considering land use multi-suitability, land resource scarcity and the diversity of human needs, the corresponding evaluation index system was constructed, respectively, and the linear weighted sum model was used to calculate the land use conflict index. Taking Jinan as the study area, the spatial distribution characteristics of land use conflicts are accurately identified and analyzed. The results show that: (1) Land use multi-suitability in Shanghe county and Jiyang district is high, but the intensity of land use conflict is not. This indicates that land use multi-suitability is the premise and basis of land use conflict, but it is not the only determinant, which is consistent with our hypothesis. (2) Land use conflicts in Jinan were dominant by medium conflict, accounting for 43.89% of the conflicts, while strong and weak land use conflicts accounted for 25.21% and 30.90% of the conflicts, respectively. The spatial distribution of land use conflicts is obviously different, with high conflicts in the north and low conflicts in the south. Strong land use conflicts are concentrated in the urban and rural transition zones of Tianqiao, Huaiyin and Shizhong districts and in the northern parts of Licheng and Zhangqiu districts. (3) Inefficient land use and land resource waste aggravated regional land use conflicts in Licheng and Zhangqiu districts. (4) The new framework for land use conflict identification proposed in this study can accurately identify land use conflicts, providing a scientific reference and new ideas for accurate identification of land use conflicts.

Biomass and bioenergy play a central role in Europe’s Green Transition. Currently, biomass is representing half of the renewable energy sources used. While the role of renewables in the energy mix is undisputed, there have been many controversial discussions on the use of biomass for energy due to the “food versus fuel” debate. Using previously underutilized lands for bioenergy is one possibility to prevent this discussion. This study supports the attempts to increase biomass for bioenergy through the provision of improved methods to identify underutilized lands in Europe. We employ advanced analysis methods based on time series modelling using Sentinel-2 (S2) data from 2017 to 2019 in order to distinguish utilized from underutilized land in twelve study areas in different bio-geographical regions (BGR) across Europe. The calculated parameters of the computed model function combined with temporal statistics were used to train a random forest classifier (RF). The achieved overall accuracies (OA) per study area vary between 80.25 and 96.76%, with confidence intervals (CI) ranging between 1.77% and 6.28% at a 95% confidence level. All in all, nearly 500,000 ha of underutilized land potentially available for agricultural bioenergy production were identified in this study, with the greatest amount mapped in Eastern Europe.

As the transition zone between urban and rural, the metropolis fringe is an area where various functions permeate and compete fiercely with each other. Understanding land use functions (LUFs) and their relationships are crucial for both urban and rural sustainable development. In this study, we established a conceptual framework of land use multifunctions in the urban fringe and proposed an improved evaluation method to quantify LUFs at the grid scale. The bivariate spatial autocorrelation method was used to explore the trade-offs among LUFs. Taking Qingpu District in Shanghai as a case study, we found that LUFs displayed pronounced spatiotemporal heterogeneity. The economic- and social-dominated functional trade-off mainly occurred in the east part of Qingpu, whereas the ecological function dominated in the west. Human preference and corresponding policies were the key factors leading to these trade-offs. Additionally, land use function zoning was proposed to resolve existing conflicts. These findings can provide scientific information for efficient land use management in the metropolis fringe.

The definition of shoreline is not the same for all contexts, and it is often a subjective matter. Various methods exist that are based on the use of different instruments that can determine and highlight a shoreline. In recent years, numerous studies have employed photogrammetric methods, based on different colours, to map the boundary between water and land. These works use images acquired by satellites, drones, or cameras, and differ mainly in terms of resolution. Such methods can identify a shoreline by means of automatic, semi-automatic, or manual procedures. The aim of this work is to find and promote a new and valid beach topography-based algorithm, able to identify the shoreline. We apply the Structure from Motion (SfM) techniques to reconstruct a high-resolution Digital Elevation Model by means of a drone for image acquisition. The algorithm is based on the variation of the topographic beach profile caused by the transition from water to sand. The SfM technique is not efficient when applied to reflecting surfaces like sea water resulting in a very irregular and unnatural profile over the sea. Taking advantage of this fact, the algorithm searches for the point in the space where a beach profile changes from irregular to regular, causing a transition from water to land. The algorithm is promoted by the release of a QGIS v3.x plugin, which allows the easy application and extraction of other shorelines.

The relevance and timeliness of ensuring the territorial development of land use at the regional level is deter-mined. The aim of the study is to develop conceptual provisions and a methodological approach to determining and assessing the territorial development of land use in regions. To achieve this goal, the following tasks are solved: identification of problems in the system for ensuring the territorial development of land use in the regions; the formation of conceptual provisions for determining the territorial development of regional lands; development of a methodological approach to assessing the level of territorial development of land use. The problematic aspects are identified and a definition of the concept of «territorial development of land use in the region» is proposed. The directions of the development and implementation of a methodological approach to assessing the territorial development of land use in the regions are described. As a result of the study, an integral indicator of the territorial development of land use in the region was determined, the value of which indicates the need to change its trends by taking measures and developing scientifically sound recommendations for ensuring the territorial development of land use for the transition from a moderate scenario to a growth scenario. Keywords: land use, territorial development of regions, conceptual provisions, methodological approach, as-sessment.

Turbulent periods of transition from socialism to neoliberal capitalism, which have affected the relationships between holders of power and governing structures in Serbia, have left a lasting impact on the urban spaces of Belgrade’s cityscape. The typical assumption is that the transformation of the urban form in the post-socialist transition is induced by planning interventions which serve to legitimize these neoliberal aspirations. The methodological approach of this paper is broadly structured as a chronological case analysis at three levels: the identification of three basic periods of institutional change, historical analysis of the urban policies that permitted transformation of the subject area, and morphogenesis of the selected site alongside the Sava River in New Belgrade. Neoliberal aspirations are traced through the moments of destruction and moments of creation as locally specific manifestations of neoliberal mechanisms observable through the urban form. Comparison of all three levels of the study traces how planning and political decisions have affected strategic directions of development and, consequently, the dynamics and spatial logic of how new structures have invaded the street frontage. The paper demonstrates that planning interventions in the post-socialist transition period, guided by the neoliberal mechanisms, has had a profound impact on the super-block morphology.

Purpose Industrial land renewal is a significant constituent of urban environment and sustainable development. Most implementation in planning of renewal of industrial land has been mainly conducted at the site level of industrial zones or parks and the larger scale of township planning deserve further attention in China. To fill this gap, this paper aims to investigate the implementation of industrial land renewal for a whole urbanized area under the township master planning. Design/methodology/approach This study introduces a progressive approach to identify and evaluate the renewal of industrial land in township master planning to move toward a more practical understanding of industrial transition. The authors chose a typical industrialized town, Lijia in Changzhou City, under the development model of “Southern Jiangsu” to explain the measurement and assessment framework to identify and evaluate the renewable industrial land. Synthesizing the idea of sustainable development, the authors investigated the renewable industrial land with an econometric model including multiple-indexes of economic, social and ecological aspects, field observations and depth interviews. Findings The analysis demonstrated the spatial heterogeneity and complex generous structure of industrial land renewal in developing countries. It pointed out the major responsibility of enterprises as main industrial land users and indispensable responsibility of government and society. Following the idea of organic concentration and avoiding one-size-fits-all kind of deal, the master planning of Lijia emphasized the connection of industrial land and the combination of market force, social force and government regulation. Originality/value With original data and discussion, the authors provide more scientific renewal strategies for planners in sustainable development.

Abstract Damage to conservation areas in North Sumatra can be mitigated by understanding the pattern of land cover change, which can be performed by detecting hotspots and their temporal and spatial patterns. This study aimed to explore land cover spatially and temporally before and after forest fires in the conservation areas in North Sumatra. Data on the hotspots, satellite imagery, land cover maps, and field verification were used to see the transition of land cover changes before and after forest and land fires. Temporal and spatial analysis was employed to see the trend of land cover changes of the land before and after the fires. Field verification was conducted through observations and interviews related to land cover conditions in the field caused by forest and land fires. This study found three conservation areas with the highest number of hotspots in 2014 in the period 2001-2019, including Gunung Leuser National Park (GLNP), Dolok Surungan Wildlife Reserve, and Barumun Wildlife Reserve during the 2001-2019 period. In 2010 and 2014 there were strong indications of a large area of land burning in three conservation areas. The burned land was near the outer boundary of the conservation areas and continued to expand into the areas over time. The area of the non-forest cover was relatively stable between periods prior to the discovery of several hotspots. Changes in forest cover to non-forest have become more widespread after the highest number of hotspots were detected in 2010. Conservation area management and various parties need to prevent the expansion of forest clearing considering the strategic role especially in GNLP as a world heritage.

Les composés Organiques Volatils (COVs) sont des gaz carbonés rares, émis en faible concentration depuis les surfaces continentale et marine vers l’atmosphère. Très réactifs, ces composés sont impliqués dans la chimie atmosphérique et sont au cœur de nombreuses problématiques environnementales actuelles telles que le changement climatique lié aux gaz à effet de serre, la qualité de l’air et les rétroactions sur le fonctionnement des écosystèmes. Les couverts végétaux terrestres étaient jusqu’alors identifiés comme les sources principales de COVs d’origine biogénique. Mais, de récentes études suggèrent que les sols pourraient constituer des sources majeures de COVs. Or dans les paysages anthropisés agricoles, les sols sont l’objet d’usages et de gestions divers et variés et sont susceptibles de modifier qualitativement et quantitativement les patrons d’émissions de COVs. Paradoxalement, les sols d’agrosystèmes ont fait l’objet de peu d’inventaires de leurs émissions de COVs. La rareté des connaissances sur la contribution des sols d’agrosystèmes dans les émissions de COVs a motivé ce travail de thèse dans lequel trois objectifs ont été poursuivis : i) inventorier les spectres et quantifier les flux de COVs émis par les sols dans les paysages agricoles, ii) déterminer le rôle des microorganismes du sol dans les émissions et iii) identifier les déterminants abiotiques régulant les émissions de COVs par les sols. Une première partie du travail a consisté à analyser les dynamiques temporelles d’émissions de COVs sur le terrain, dans deux sites observatoires représentatifs du paysage agricole Breton : le site EFELE (SOERE-PRO) comprenant des sols cultivés soumis à des pratiques de fertilisation contrastées, et la Zone Atelier Armorique (ZAAr) comprenant des prairies permanentes fertilisées et des prairies humides caractérisées par un faible degré d’anthropisation. La deuxième partie du travail a été menée en laboratoire pour expliciter et compléter les observations de terrain, deux séries d’expérimentations en laboratoire ont été réalisées permettant de manipuler, i) la source de carbone organique du sol via l’apport de différentes molécules modèles, ii) les communautés microbiennes par la transplantation de communautés microbiennes naturelles dans trois sols distincts. Cette étude aura permis de montrer, en laboratoire et sur le terrain, qu’un sol émet une quarantaine de masses dont seules quelques-unes (1 à 4) sont dominantes. Ces spectres de COVs sont par ailleurs spécifiques des usages des sols (culture vs prairie) et des pratiques de fertilisation. Nous montrons aussi : i) qu’il existe une temporalité des émissions de COVs par les sols allant de 22 à 167 μg de COVs par m−2 h−1, la période hivernale étant la moins émissive et que ii) s’ajoute que certaines pratiques de fertilisation, comme l’apport de lisier de porc, induisent un flux de méthanol pouvant atteindre jusqu’à 10 fois celui qui est observé par les sols amendés avec du digestat de lisier de porc. Concernant, le rôle des microorganismes du sol dans la production de COVs, nous démontrons que le spectre de COVs n’est pas représentatif de la diversité phylogénétique de la communauté du sol mais plutôt de l’activité métabolique des microorganismes actifs. S’agissant de l’exploration des déterminants abiotiques susceptibles de réguler les émissions, nos résultats suggèrent que l’ajout de molécules organiques au sol, induit un changement rapide dans le spectre de COVs émis par le sol. Cette modification est dépendante du degré de polymérisation de la molécule apportée. Pour conclure, l’approche intégrative et interdisciplinaire mise en œuvre dans ce travail de thèse a permis d’accroître les connaissances sur les émissions de COVs biogéniques par les sols. L’ensemble des recherches suggère que les émissions de COVs par les sols ne sont pas négligeables. Leur position dans les cycles biogéochimiques nécessite leur intégration dans les scenarii futurs des changements globaux
Volatile Organic Compounds (VOCs) are trace carbonaceous gases emitted in low concentrations from the continental and marine surfaces to the atmosphere. Highly reactive, these compounds are involved in atmospheric chemistry and are at the heart of many current environmental issues such as climate change related to greenhouse gases, air quality and feedback on the functioning of ecosystems. Terrestrial plant cover was previously identified as the main source of VOCs of biogenic origin. But recent studies suggest that soils could be major sources of VOCs. However, in agricultural anthropogenic landscapes, soils are subject to various and varied uses and management and are likely to modify qualitatively and quantitatively the patterns of VOC emissions. Paradoxically, agrosystem soils have been the subject of few inventories of their VOC emissions. The scarcity of knowledge on the contribution of agrosystems soils in VOC emissions motivated this work of thesis in which three objectives were pursued : i) inventory the spectra and quantify the VOCs fluxes emitted by soils in agricultural landscapes (ii) to determine the role of soil microorganisms in emissions and (iii) to identify the abiotic determinants controlling VOC emissions by soils. A first part of the work has consisted in analyzing the temporal dynamics of VOCs emissions in the field, in two observatory sites representative of the Britain agricultural landscape : the EFELE site (SOERE-PRO) comprising cultivated soils subjected to contrasting fertilization practices, and the Zone Atelier Armorique (ZAAr) including fertilized permanent meadows and wet meadows characterized by a low degree of anthropization. The second step of the work was conducted in the laboratory to clarify and complete the field observations, two series of laboratory experiments were conducted to manipulate, i) the soil organic carbon source via the input of different model molecules (ii) microbial communities by transplanting natural microbial communities into three distinct soils. This study has generated technical advances and produced entirely new results concerning both the characterization of spectra and the quantification of biogenic VOC fluxes emitted by soils. Thus, we show, in the laboratory and in the field, that a soil emits about forty masses of which only a few (1 to 4) are dominant. These VOC spectra are also specific to land uses (crop vs meadow) and fertilization practices. We also show that : i) there is a temporality of VOC emissions by soils ranging from 22 to 167 μg of VOCs per m−2 h−1, the winter period is the least emissive and ii) adds that some fertilization practices, such as pig slurry, induce a flux of methanol up to 10 times that observed by soils amended with methanised pig slurry. Regarding the role of soil microorganisms in VOCs production, we demonstrate that the VOCs spectrum is not representative of the phylogenetic diversity of the soil community but rather of the metabolic activity of active microorganisms. As for the exploration of abiotic determinants that can regulate emissions, our results suggest that the addition of organic molecules to the soil induces a rapid change in the VOC spectrum emitted by the soil, ranging from a few hours to a few days after intake. This modification is dependent on the degree of polymerization of the molecule provided. All research suggests that VOC emissions by soils are not negligible. Their key position in terms of issues requires to be of greater interest and to take them into account in future scenarios of global changes (climate and land uses), especially with regard to emerging practices of soil management in connection with the ecological transition initiated in agriculture. Similarly, the consideration of VOCs emissions in the biogeochemical cycles of carbon and that of nitrogen to better understand the functioning of ecosystems is also discussed in this document

Abstract: Over-the-horizon radars (OTHRs) are HF-band systems that, via surface propagation (ground-wave or surface-wave) or ionospheric re ection (sky-wave), cover an area that is located well beyond the horizon. Though based on an assessed technology, OTHRs are attracting today much interest, thanks to the relevant improvements in signal processing and data storage techniques. By exploiting the propagation mechanisms of HF waves in the Terrestrial Atmosphere, the OTHR is able to overcome the horizon line, that represents a natural boundary for every ground-based microwave radar. In the case of sky-wave OTHR, the re flection of the signals by the Ionosphere allows the system to achieve range distances up to about 3000 km. Nevertheless, the employment of the Ionosphere as part of the propagation-channel introduces an intrinsic uncertainty about the actual HF wave propagation path and, consequently, about the actual geographic position of the radar footprint. In fact, the non-homogeneous structure and time-dependent behavior of the Ionosphere make the a priori models for the propagation channel absolutely useless for a correct Geo-referencing of the received echo. Therefore, every HF OTHR-SW application must include a process to associated the received signals to unambiguous geographic coordinates. Such a process, referred to as coordinate registration (CR), generally relies on an ionospheric model, based on seasonal and daily ionospheric statistics within the radar operating area. Several current OTHR-SW systems perform a periodic update of the ionospheric model exploiting information gathered by ionosonde networks or directly collected from the OTHR with a dedicated procedure. Both approaches exhibit several limitations, leading to a correct characterization of the ionosphere only when it is in particularly steady conditions. The present research is focused on the study and development of a new different approach to the CR problem for OTHR-SW systems. This approach, referred to as Sea/Land Transition Identification (SLTI), takes advantage from the a priori knowledge of the Geo-morphological structure of the surveillance area in order to compensate for the uncertainties introduced by the Ionosphere. In fact, as suggested by the name of the method, the shape of the coastline profiles within the surveillance area are employed as position-references for the geo-referencing of the received radar echo. This task is possible through a basic time analysis of the echo, thanks to the marked difference in the values of the HF back-scattering coefficient for sea and land regions. The SLTI method is based on the maximization of the cross-correlation between the received radar echo and the surface mask signatures for the surveillance area. It can be employed in real time by the system, during its typical surveillance routine and besides the collected data can be exploited to estimate some Ionospheric parameters in order to periodically update and correct the employed statistical model. After a general introduction about the OTHR sensors and a more detailed description of the sky-wave system who we refer to in the present work, the state of the art for the CR procedures actually employed by OTHR-SW is presented. Hence the SLTI method is outlined together with the numerical model of the whole OTHR-SW scenario. The application of the method, in this scenario simulated under simplifying operative hypothesis, is described with the help of some examples for both the CR procedure and the Ionospheric probing task. Within these examples of application of the SLTI method, the minimum requirements in terms of received signal-to-noise ratio (SNR) and differential sea/land backscattering coefficients necessary to achieve a given accuracy in the range estimate are pointed out. Finally the further developments of the SLTI method and some possible improvement of the simulated OTHR-SW's scenario are pointed out.

Sustainability and resilience have become indispensable parts of the contemporary debate over the built environment. Although recognised as imperatives, the complexity and the variety of interpretations of sustainability and resilience have raised the necessity to again rethink their notion in the context of the built environment and to reframe the state-of-the-art body of knowledge. The book Sustainability and Resilience: Socio-Spatial Perspective so begins with the exploration of the broadest conceptual frame-of-reference of issues related to sustainability, and the re-establishment of the connection between the built environment and the conditions that are vital to its functioning, primarily in relation to energy, land use, climate, and economy. Subsequent discussion on resilience as a term, approach, and philosophy aims to conceptualise an interpretation of key resilience concepts, explain relationships and links among them, and propose the classification of resilience as applicable to the context of urban studies. By studying the processes of transition of the built environment, the book then reveals a coherent formula of ‘thinking sustainability + resilience’ aimed at improving the ability to respond to disruptions and hazards while enhancing human and environmental welfare. The necessity to integrate the two approaches is further accented as a result of a deliberative discourse on the notions of ‘social sustainability’, ‘sustainable community’, and ‘socio-cultural resilience’. The potential of measuring sustainable development and urban sustainability on the basis of defined social, human, and, additionally, natural and economic values is presented though an overview of different wellknown indicators and the identification of a currently relevant tangible framework of sustainable development. Correspondingly, the role of policies and governance is demonstrated on the case of climate-proof cities. In this way, the consideration of approaches to sustainability and resilience of the urban environment is rounded, and the focus of the book is shifted towards an urban/rural dichotomy and the sustainability prospects of identified forms-in-between, and, subsequently, towards the exploration of values, challenges, and the socio-cultural role in achieving sustainability for rural areas. In the final chapters, the book offers several peculiarised socio-spatial perspectives, from defining the path towards more resilient communities and sustainable spaces based on a shared wellbeing, to proposing the approach to define community resilience as an intentional action that aims to respond to, and influence, the course of social and economic change, to deliberating the notion of a ’healthy place’ and questioning its optimal scale in the built environment. The study of sustainability and resilience in this book is concluded by drawing a parallel between environmental, economic, and social determinants of the built environment and the determinants that are relevant to human health and well-being.

AbstractThis book has introduced two new (linked) models for greyfield precinct regeneration—place-activated and transit-activated GPR—with a new set of processes to enable them. The need for new design, planning, and engagement tools that must be integrated into all urban development is also seen as key to unlocking greyfield regeneration. Designs for such precincts have proliferated, but planning systems are still hindering their implementation, especially those systems related to land-assembly issues in the established, occupied middle greyfield suburbs. Planning must change, and a potential way ahead involves the planning processes demonstrated in this book. A first step involves district greenlining, which enables identification of strategic planning challenges and priorities for action at a district scale along a transit corridor (transit-activated GPR) or in precinct-scale areas in typical middle suburbs with high redevelopment potential (place-activated GPR). Their key attributes are gleaned from the previous chapters and summarised in this chapter. A final plea is made here for partnerships to be created from the engagement of all stakeholders: government, community and civil society, innovators, and developers. Greyfield Precinct Redevelopment Authorities established within state governments as part of a federal Better Cities 2.0 program could guide this transition.

In the previous chapters, the use of geophysical data for delineating the continental shelf has been discussed in some detail. But the determination of the case for any extension of the legal continental shelf beyond 200 nautical miles (M) from the territorial sea baseline may in some circumstances require a geological survey to confirm that a topographic or geophysical feature comprising what appears to be a natural prolongation of land territory is of continental or oceanic origin. A geological survey may also be necessary to determine the occurrence, thickness, and extent of sediments beyond the foot of the slope. Continental margins represent regions of transition from the landmass to the ocean basin and may be present-day areas of sediment erosion or deposition. Sediment supply to the continental shelf and slope, or the extent of erosion on the continental shelf and upper slope, is influenced by tectonic activity, sea-level fluctuations, climate change, variation in the wave or current regime, and various other processes. Bottom currents or gravity transport (turbidity) processes combine to varying degrees with pelagic sedimentation (the accumulation of the remains of marine organisms) to extend the supply of sediment well beyond the shelf and slope to the continental rise, ocean trench, or abyssal plain (Evans et al., 1998). In order to understand the geology of such areas, it is necessary to determine the structural setting, the tectonic and sedimentary evolution, the chrono-and lithostratigraphy, and the volcanic history. Understanding the ocean floor is a prerequisite for the determination of the extent of the continental shelf under UNCLOS. It is also highly relevant to the identification and delineation of mineral and energy resources, for determining the waste disposal potential of parts of the seafloor, and for undertaking an assessment of the risk of slope failure. None of these are directly relevant to establishing the new limits of the continental shelf, but they are highly relevant to its long-term exploitation. In order to achieve the necessary level of knowledge, the seafloor morphology and seabed character derived from bathymetric and sonar surveys (described in chapters 9 and 10) and the three-dimensional geology determined by geophysical surveys using seismic profiling, magnetometer, and gravity meter (discussed in chapters 12 and 13) need to be calibrated or "ground truthed" by sampling and coring (figure 14.1; Stoker et al., 1994).

Through numerical simulations, this paper examines the nature of instability mechanisms leading to transition in separation bubbles. The results of two direct numerical simulations are presented in which separation of a laminar boundary layer occurs over a flat surface in the presence of an adverse pressure gradient. The primary difference in the flow conditions between the two simulations is the level of freestream turbulence with intensities of 0.1% and 1.45% at separation. In the first part of the paper, transition under a low-disturbance environment is examined, and the development of the Kelvin-Helmholtz instability in the separated shear layer is compared to the well-established instability characteristics of free shear layers. The study examines the role of the velocity-profile shape on the instability characteristics and the nature of the large-scale vortical structures shed downstream of the bubble. The second part of the paper examines transition in a high-disturbance environment, where the above-mentioned mechanism is bypassed as a result of elevated freestream turbulence. Filtering of the freestream turbulence into the laminar boundary layer results in streamwise streaks which provide conditions under which turbulent spots are produced in the separated shear layer, grow, and then merge to form a turbulent boundary layer. The results allow identification of the structure of the instability mechanism and the characteristic structure of the resultant turbulent spots. Recovery of the reattached turbulent boundary layer is then examined for both cases. The large-scale flow structures associated with transition are noted to remain coherent far downstream of reattachment, delaying recovery of the turbulent boundary layer to an equilibrium state.

With the new generation of gas turbine engines, low Reynolds number flows have become increasingly important. Designers must properly account for transition from laminar to turbulent flow and separation of the flow from the suction surface, which is strongly dependent upon transition. Of interest to industry are Reynolds numbers based upon suction surface length and flow exit velocity below 150,000 and as low as 25,000. In this paper, the extreme low end of this Reynolds number range is documented by way of pressure distributions, loss coefficients and identification of separation zones. Reynolds numbers of 25,000 and 50,000 and with 1% and 8–9% turbulence intensity of the approach flow (Free Stream Turbulence Intensity, FSTI) were investigated. At 25,000 Reynolds number and low FSTI, the suction surface displayed a strong and steady separation region. Raising the turbulence intensity resulted in a very unsteady separation region of nearly the same size on the suction surface. Vortex generators were added to the suction surface, but they appeared to do very little at this Reynolds number. At the higher Reynolds number of 50,000, the low-FSTI case was strongly separated on the downstream portion of the suction surface. The separation zone was eliminated when the turbulence level was increased to 8–9%. Vortex generators were added to the suction surface of the low-FSTI case. In this instance, the vortices were able to provide the mixing needed to reestablish flow attachment. This paper shows that massive separation at very low Reynolds numbers (25,000) is persistent, in spite of elevated FSTI and added vortices. However, at a higher Reynolds number, there is opportunity for flow reattachment either with elevated freestream turbulence or with added vortices. This may be the first documentation of flow behavior at such low Reynolds numbers. Though undesirable to operate under these conditions, it is important to know what to expect and how performance may be improved if such conditions are unavoidable.