Coastal and estuarine habitat mapping, using LIDAR height and intensity and multi-spectral imagery   总被引：3，自引：1，他引：2  

Guillem Chust  Ibon Galparsoro  ngel Borja  Javier Franco  Adolfo Uriarte 《Estuarine, Coastal and Shelf Science》2008,78(4):633-643

The airborne laser scanning LIDAR (LIght Detection And Ranging) provides high-resolution Digital Terrain Models (DTM) that have been applied recently to the characterization, quantification and monitoring of coastal environments. This study assesses the contribution of LIDAR altimetry and intensity data, topographically-derived features (slope and aspect), and multi-spectral imagery (three visible and a near-infrared band), to map coastal habitats in the Bidasoa estuary and its adjacent coastal area (Basque Country, northern Spain). The performance of high-resolution data sources was individually and jointly tested, with the maximum likelihood algorithm classifier in a rocky shore and a wetland zone; thus, including some of the most extended Cantabrian Sea littoral habitats, within the Bay of Biscay. The results show that reliability of coastal habitat classification was more enhanced with LIDAR-based DTM, compared with the other data sources: slope, aspect, intensity or near-infrared band. The addition of the DTM, to the three visible bands, produced gains of between 10% and 27% in the agreement measures, between the mapped and validation data (i.e. mean producer's and user's accuracy) for the two test sites. Raw LIDAR intensity images are only of limited value here, since they appeared heterogeneous and speckled. However, the enhanced Lee smoothing filter, applied to the LIDAR intensity, improved the overall accuracy measurements of the habitat classification, especially in the wetland zone; here, there were gains up to 7.9% in mean producer's and 11.6% in mean user's accuracy. This suggests that LIDAR can be useful for habitat mapping, when few data sources are available. The synergy between the LIDAR data, with multi-spectral bands, produced high accurate classifications (mean producer's accuracy: 92% for the 16 rocky habitats and 88% for the 11 wetland habitats). Fusion of the data enabled discrimination of intertidal communities, such as Corallina elongata, barnacles (Chthamalus spp.), and stands of Spartina alterniflora and Phragmites australis, which presented misclassification when conventional visible bands were used alone. All of these results were corroborated by the kappa coefficient of agreement. The high classification accuracy found here, selecting data sources, highlights the value of integrating LIDAR data with multi-spectral imagery for habitat mapping in the intertidal complex fringe.  相似文献   

Testing the stereoscopic precision of a large-format digital camera     

Benjamín  Arias  Javier  Gómez-Lahoz 《The Photogrammetric Record》2009,24(126):157-170

The use of large-format digital cameras in aerial photogrammetry is leading to great improvements in photogrammetric production. Since they were first introduced about 10 years ago, the technological community has been testing and investigating the conditions under which this major change can be consolidated. But a certain (and understandable) bias may be noticed in the efforts that developers, researchers and clients are undertaking. Almost all of the efforts aim at checking the quality of automated measurements and very little attention has been directed to stereoscopic measurements by human operators, which, nevertheless, still represent an important task that needs to be carried out in the production chain. This paper presents the results from a number of tests (13 operators from a variety of enterprises) performed to check the stereoscopic precision of Vexcel UltraCamD camera images compared with Leica RC30 film images. The main conclusion to be drawn from the empirical data is that stereoscopic precision does not depend on the type of camera.  相似文献   

Welcome mats? The role of seagrass meadow structure in controlling post-settlement survival in a keystone sea-urchin species     

Patricia Prado  Javier Romero  Teresa Alcoverro 《Estuarine, Coastal and Shelf Science》2009

Processes acting on the early-life histories of marine organisms can have important consequences for the structuring of benthic communities. In particular, the degree of coupling between larval supply and adult abundances can wield considerable influence on the strength of trophic interactions in the ecosystem. These processes have been relatively well described in rocky systems and soft-sediment communities, and it is clear that they are governed by very different bottlenecks. Seagrass meadows make interesting study systems because they bear structural affinities to both soft sediments as well as rocky substrates. We examined the early-life history of Paracentrotus lividus, one of the dominant herbivores in Mediterranean seagrass meadows, to identify the drivers of population dynamics in this species. We measured spatial and temporal variability in sea urchin post-settlement in 10 Posidonia oceanica meadows in the North-Western Mediterranean over a period of two years, and compared the numbers with the one-year old cohort a year later (i.e. the new population recruitment) as well as between successive size–age groups. Urchin post-settlers differed substantially between meadows but were present in both years in all meadows surveyed, suggesting that larval supply was not limiting for any of the studied sites. However, in six of the studied meadows, the one-year cohort of urchins was absent in both years, indicating that post-settlement processes strongly affected urchins in these meadows. In contrast, in four of the studied meadows, there was a strong coupling between post-settlers and one-year cohort individuals. These meadows were structurally different from the others in that they were characterised by an exposed matrix of rhizomes forming a dense seagrass mat. This mat apparently strongly mediates post-settlement mortality, and its presence or absence dictates the successful establishment of urchin populations in seagrass meadows. As the population aged, the relationship between size–age groups decreased evidencing the action of other processes. Yet, these results indicate that differences in physical structure are a vital bottleneck for sea urchin populations in seagrass meadows. Exploring the interaction between ecosystem structure and early-life history may provide a broader and more unified framework to understand the dynamics of a range of benthic habitats, including rocky substrates, soft sediments and seagrass meadows.  相似文献   

Twist transport in strongly torsioned astrophysical flux tubes     

L. C. Garcia de Andrade 《Astrophysics and Space Science》2007,310(1-2):25-29

Riemannian geometrical effects on the expansion of the electron magnetohydrodynamical (EMH) superconductivity modeled twisted nonplanar thin magnetic flux tubes are considered. A solution is found which represents almost incompressible plasma flows, where the twist of flux tube is computed in terms of the continuous variation of its cross-section. It is shown that the twist increases in regions where twisted flux tube expands as in Parker’s conjecture. From computation of compression along the tube we show that when the torsion is weak a centrifugal or vorticity effect on the longitudinal direction of the tube enhances the screening effect on the “superconductor”. Throughout the paper we consider helical flux tubes where torsion and curvature of the tube are constants. Thus we show that the Parker’s conjecture is valid in a continuos manner for these type II superconducting twisted flux tubes. Throughout the paper we adopt the approximation that the radial component of the magnetic field varies so slowly along the tube axis that it can be approximated to zero along the tube. It is suggested that the models discussed here may also be applied to DNA and nanotubes.  相似文献   

Results from MAGIC’s first observation cycle on galactic sources     

Javier Rico 《Astrophysics and Space Science》2007,309(1-4):285-291

During its Cycle I (2005/2006), the MAGIC telescope targeted about 250 hours several galactic γ-ray sources detected previously by other experiments or expected to emit in the same energy domain. This paper reviews some results of such MAGIC observations. We cover, among others, supernova remnants, the Galactic Center and microquasars. We will concentrate on the recent discovery of very high energy γ-rays from the microquasar LS I +61 303.  相似文献   

Integrability of motion around galactic razor-thin disks     

Ronaldo?S.?S.?VieiraEmail author  Javier?Ramos-Caro 《Celestial Mechanics and Dynamical Astronomy》2016,126(4):483-500

We consider the three-dimensional bounded motion of a test particle around razor-thin disk configurations, by focusing on the adiabatic invariance of the vertical action associated with disk-crossing orbits. We find that it leads to an approximate third integral of motion predicting envelopes of the form \(Z(R)\propto [\varSigma (R)]^{-1/3}\), where R is the radial galactocentric coordinate, Z is the z-amplitude (vertical amplitude) of the orbit and \(\varSigma \) represents the surface mass density of the thin disk. This third integral, which was previously formulated for the case of flattened 3D configurations, is tested for a variety of trajectories in different thin-disk models.  相似文献   

WSO and the winds of massive stars: the gate to the metal-poor Local Universe     

Miriam Garcia  Artemio Herrero  Francisco Najarro 《Astrophysics and Space Science》2011,335(1):91-96

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the λ < 1200 Å wavelengths is critical as it contains important diagnostic lines for mass loss and shocks in the wind, as found by FUSE-based analyses.WSO will enable quantitative spectroscopic analyses of blue massive stars in the Local Group beyond the Magellanic Clouds. The results will lead to the characterization of their winds as a function of metallicity, and shed new light on current urging questions regarding radiation driven winds.  相似文献   

A multivariate index based on the seagrass Posidonia oceanica (POMI) to assess ecological status of coastal waters under the water framework directive (WFD)     

Romero J  Martínez-Crego B  Alcoverro T  Pérez M 《Marine pollution bulletin》2007,55(1-6):196-204

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Uncovering spatiotemporal micromobility patterns through the lens of space–time cubes and GIS tools     

Arias-Molinares  Daniela  García-Palomares  Juan Carlos  Romanillos  Gustavo  Gutiérrez  Javier 《Journal of Geographical Systems》2023,25(3):403-427

Journal of Geographical Systems - In the past ten years, cities have experienced a burst of micromobility services as they offer a flexible transport option that allows users to cover short trips...  相似文献   

Pockmarks on either side of the Strait of Gibraltar: formation from overpressured shallow contourite gas reservoirs and internal wave action during the last glacial sea-level lowstand?     

Ricardo León  Luis Somoza  Teresa Medialdea  Francisco Javier González  Carmen Julia Gimenez-Moreno  Raúl Pérez-López 《Geo-Marine Letters》2014,34(2-3):131-151

Integrating novel and published swath bathymetry (3,980 km²), as well as chirp and high-resolution 2D seismic reflection profiles (2,190 km), this study presents the mapping of 436 pockmarks at water depths varying widely between 370 and 1,020 m on either side of the Strait of Gibraltar. On the Atlantic side in the south-eastern Gulf of Cádiz near the Camarinal Sill, 198 newly discovered pockmarks occur in three well localized and separated fields: on the upper slope (n=14), in the main channel of the Mediterranean outflow water (MOW, n=160), and on the huge contourite levee of the MOW main channel (n=24) near the well-known TASYO field. These pockmarks vary in diameter from 60 to 919 m, and are sub-circular to irregularly elongated or lobate in shape. Their slope angles on average range from 3° to 25°. On the Mediterranean side of the strait on the Ceuta Drift of the western Alborán Basin, where pockmarks were already known to occur, 238 pockmarks were identified and grouped into three interconnected fields, i.e. a northern (n=34), a central (n=61) and a southern field (n=143). In the latter two fields the pockmarks are mainly sub-circular, ranging from 130 to 400 m in diameter with slope angles averaging 1.5° to 15°. In the northern sector, by contrast, they are elongated up to 1,430 m, probably reflecting MOW activity. Based on seismo-stratigraphic interpretation, it is inferred that most pockmarks formed during and shortly after the last glacial sea-level lowstand, as they are related to the final erosional discontinuity sealed by Holocene transgressive deposits. Combining these findings with other existing knowledge, it is proposed that pockmark formation on either side of the Strait of Gibraltar resulted from gas and/or sediment pore-water venting from overpressured shallow gas reservoirs entrapped in coarse-grained contourites of levee deposits and Pleistocene palaeochannel infillings. Venting was either triggered or promoted by hydraulic pumping associated with topographically forced internal waves. This mechanism is analogous to the long-known effect of tidal pumping on the dynamics of unit pockmarks observed along the Norwegian continental margin.  相似文献