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991.
Reliable and up-to-date urban land cover information is valuable in urban planning and policy development. Due to the increasing demand for reliable land cover information there has been a growing need for robust methods and datasets to improve the classification accuracy from remotely sensed imagery. This study sought to assess the potential of the newly launched Landsat 8 sensor’s thermal bands and derived vegetation indices in improving land cover classification in a complex urban landscape using the support vector machine classifier. This study compared the individual and combined performance of Landsat 8’s reflective, thermal bands and vegetation indices in classifying urban land use-land cover. The integration of Landsat 8 reflective bands, derived vegetation indices and thermal bands overall produced significantly higher accuracy classification results than using traditional bands as standalone (i.e. overall, user and producer accuracies). An overall accuracy above 89.33% and a kappa index of 0.86, significantly higher than the one obtained with the use of the traditional reflective bands as a standalone data-set and other analysis stages. On average, the results also indicate high producer and user accuracies (i.e. above 80%) for most of the classes with a McNemar’s Z score of 9.00 at 95% confidence interval showing significant improvement compared with classification using reflective bands as standalone. Overall, the results of this study indicate that the integration of the Landsat 8’s OLI and TIR data presents an invaluable potential for accurate and robust land cover classification in a complex urban landscape, especially in areas where the availability of high resolution datasets remains a challenge. 相似文献
992.
Silvania Avelar Tessa S. van der Voort Timothy I. Eglinton 《Carbon balance and management》2017,12(1):10
Background
Determining national carbon stocks is essential in the framework of ongoing climate change mitigation actions. Presently, assessment of carbon stocks in the context of greenhouse gas (GHG)-reporting on a nation-by-nation basis focuses on the terrestrial realm, i.e., carbon held in living plant biomass and soils, and on potential changes in these stocks in response to anthropogenic activities. However, while the ocean and underlying sediments store substantial quantities of carbon, this pool is presently not considered in the context of national inventories. The ongoing disturbances to both terrestrial and marine ecosystems as a consequence of food production, pollution, climate change and other factors, as well as alteration of linkages and C-exchange between continental and oceanic realms, highlight the need for a better understanding of the quantity and vulnerability of carbon stocks in both systems. We present a preliminary comparison of the stocks of organic carbon held in continental margin sediments within the Exclusive Economic Zone of maritime nations with those in their soils. Our study focuses on Namibia, where there is a wealth of marine sediment data, and draws comparisons with sediment data from two other countries with different characteristics, which are Pakistan and the United Kingdom.Results
Results indicate that marine sediment carbon stocks in maritime nations can be similar in magnitude to those of soils. Therefore, if human activities in these areas are managed, carbon stocks in the oceanic realm—particularly over continental margins—could be considered as part of national GHG inventories.Conclusions
This study shows that marine sediment organic carbon stocks can be equal in size or exceed terrestrial carbon stocks of maritime nations. This provides motivation both for improved assessment of sedimentary carbon inventories and for reevaluation of the way that carbon stocks are assessed and valued. The latter carries potential implications for the management of human activities on coastal environments and for their GHG inventories.993.
994.
995.
Timothy W. Barash Charles G. Doll Jr. John A. Collins George H. Sutton Sean C. Solomon 《Marine Geophysical Researches》1994,16(5):347-363
A problem in the use of ocean bottom seismometers is the difficulty in leveling the sensors while ensuring good coupling to the seafloor. We have investigated the coupling characteristics of the seismic sensors in the new ONR ocean bottom seismometer. In the deployable sensor package for that instrument, a three-component seismometer set is suspended on a 2-axis passive leveling gimbal and is immersed in a viscous fluid. We report tests, conducted in a seismic vault, comparing the output of a gimbaled seismometer set to that of a set rigidly coupled to the ground. Our results show that the degree to which the gimbaled set is coupled to ground motion is a function of the viscosity of the coupling fluid. The coherence between the two sensor sets is poor (<0.4) at some frequencies within the band of interest (0.15 to 20 Hz) and on some components when the viscosity of the coupling fluid is comparatively low (14 Pa-s or 0.16 kSt kinematic viscosity). In addition, the outputs of some components over portions of this frequency band are attenuated and are phase-shifted relative to the outputs of the set rigidly coupled to the ground. Coherence and phase response similarity improve as the viscosity of the coupling fluid is increased. With a coupling fluid viscosity of 980 Pa-s (10 kSt), coherence and phase agreement between the two sensor sets is good (>0.9) across nearly the entire band of interest on all three components. A simple analytical model of the gimbaled seismometer set as a damped, driven, compound-pendulum provides a basis for understanding the test results. 相似文献
996.
Philip P. Newton Richard S. Lampitt Timothy D. Jickells Penny King Clare Boutle 《Deep Sea Research Part I: Oceanographic Research Papers》1994,41(11-12)
Particle fluxes to 3100 m depth at 45°50′N, 19°30′W were measured using time-series sediment traps during a 17 month period encompassing 1989 and 1990 JGOFS spring bloom process studies in the northeast Atlantic. There was a marked intra-annual variability in fluxes of mass, particulate inorganic carbon (PIC), particulate organic carbon (POC) and opal, appearing as two major flux events in each year. In 1989, the first flux event represented the settlement of spring bloom-type material, whereas the second, in autumn, was heavily enriched in mucopolysaccharides. In 1990, in contrast, the two flux events comprised spring bloom-type material and arrived at depth at different times relative to the 1989 events. The intra- and interannual variability evident for all three biogenic components was most notable for POC: (i) the autumn 1989 event supplied twice as much POC to 3100 m as the earlier spring bloom settlement—a quite unexpected observation—and (ii) the annual average POC flux in 1989 was 3–4 times more than in 1990. A synthesis of process study datasets with sediment trap data enables an evaluation of the coupling of deep fluxes with surface-water events. Spatial variability of the 1989 deep flux events is assessed by comparing the sediment trap data reported here with those from a second site 100 km away (Honjo and Manganini,Deep-Sea Research II,40, 587–607, 1993). The timing and magnitude of the 1989 spring bloom settlement was indistinguishable in the two datasets, indicating no spatial variability in flux between these sites. In contrast, the autumn 1989 flux event was barely recorded at the second site. Given the biogeochemical importance of this latter event to deep waters, most notable in terms of its contribution to POC flux, this observation of deep-water mesoscale flux variability indicates a significant problem in determining regional carbon budgets. Construction of basin-scale budgets is a central goal of JGOFS and for this to be achieved further studies of mesoscale variability of particle flux are essential. 相似文献
997.
Thomas M Iliffe Timothy D Jickells Martin S Brewer 《Marine environmental research》1984,12(3):173-189
Inland marine caves have served as biological refugia and, as such, frequently contain unique assemblages of taxonomically significant relict populations known only from a single cave or cave system. However, the absence of photosynthesis in this totally lightless environment and the presence of a highly stratified water column and long residence times for cave waters, characteristically result in depleted dissolved oxygen levels. Under such circumstances, organic pollution, even at low levels, can produce anoxic conditions and may consequently result in the extinction of entire species of cavernicolous fauna. We here present data on the normal environment of marine caves in Bermuda and cite as an example a cave which has become grossly polluted as a result of indiscriminate dumping. 相似文献
998.
Remnants of an Eocene fan system are preserved onshore at San Diego and in the central part of the southern California borderland. Even though faults and erosion have truncated its margins, geophysical data and exploratory wells indicate that remaining parts of the fan extend beneath an offshore area nearly 400-km long and 40- to 100-km wide. Environments representing fluvial, fan-delta, shelf-channel, overlapping inner- to outer-fan, and basin-plain facies are recognized or inferred. Three progradational cycles onshore and two distinct pulses of sand accumulation offshore are attributable to eustatic low sea-level stands rather than to tectonic uplift or shifts in depositional patterns. 相似文献
999.
R. Howell 《Marine environmental research》1984,11(3):153-161
The acute toxicity of seawater solutions of copper, zinc, lead, cadmium and mercury to two species of free-living marine nematodes was studied. Enoplus brevis (Bastian) is a euryhaline species inhabitating intertidal estuarinemud. The closely related Enoplus communis (Bastian) is stenohaline and may be found as a commensal in the byssus threads of seed mussels. Specimens of both species were collected from two sites on the Northeast coast of England showing different levels of pollution by heavy metals. Both species were more susceptible to copper, lead and mercury than to zinc and cadmium, but the order of toxicity of the metals changed with exposure concentration. The euryhaline species survived better than the strictly marine species and there is a suggestion that animals from a polluted site were more tolerant of elevated of heavy metals. 相似文献
1000.
Sedimentary,tectonic, and sea-level controls on submarine fan and slope-apron turbidite systems 总被引:1,自引:0,他引:1
To help understand factors that influence submarine fan deposition, we outline some of the principal sedimentary, tectonic, and sea-level controls involved in deep-water sedimentation, give some data on the rates at which they operate, and evaluate their probable effects. Three depositional end-member systems, two submarine fan types (elongate and radial), and a third nonfan, slope-apron system result primarily from variations in sediment type and supply. Tectonic setting and local and global sea-level changes further modify the nature of fan growth, the distribution of facies, and the resulting vertical stratigraphic sequences. 相似文献