Since several space-borne synthetic aperture radar (SAR) instruments providing high spatial resolutions and multi-polarisation capabilities will be mounted on satellites to be launched from 2006 onwards, radar imagery promises to become an indispensable asset for many environmental monitoring applications. Due to its all weather, day and night capabilities, SAR imagery presents obvious advantages over optical instruments, especially in flood management applications. To date, however, the coarse spatial resolution of available SAR datasets restricts the information that can be reliably extracted and processing techniques tend to be limited to binary floodplain segmentation into ‘flooded’ and ‘non flooded’ areas. It is the purpose of this paper to further improve the exploitation of SAR images in hydraulic modelling and near real-time crisis management by means of developing image processing methodologies that allow for the extraction of water levels at any point of the floodplain. As high-precision digital elevation models (DEM) produced, for instance, from airborne laser scanning become more readily available, methods can be exploited that combine SAR-derived flood extent maps and precise topographic data for retrieving water depth maps. In a case study of a well-documented flood event in January 2003 on the River Alzette, Grand Duchy of Luxembourg, a root mean squared error (R.M.S.E.) of 41 cm was obtained by comparing the SAR-derived water heights with surveyed high water marks that were collected during image acquisition. Water levels that were computed by a previously calibrated hydraulic model also suggest that the water surface profiles provided by the combined use of topographic data and SAR accurately reflect the true water line. The extraction of flooded areas within vegetated areas further demonstrates the usefulness of the proposed methodology. 相似文献
We present two case studies regarding the application of Synthetic Aperture Radar (SAR) Persistent Scatterers Interferometry (PSI) techniques to landslide-prone slopes situated in the municipal territories of Caramanico Terme and Volturino (Italy). The analysis of satellite SAR data with PSI techniques poses often problems on sites where, due to the scarcity of human artefacts and the presence of vegetation cover, density of coherent points (PS) is low (< 10 per km2). Moreover, the steep and rough topography typical of landslide-prone areas hamper the interferometric pre-processing, making more difficult the joint estimation of displacements and of DEM errors. Under these conditions the significance of temporal interferometric phase trends can be uncertain and conservative assumptions, necessary to ensure low false detection probabilities, need to be coupled with innovative processing strategies to increase the detection efficiency of PS objects. Here, the SPINUA (Stable Point Interferometry over Un-urbanised Areas) processing technique is applied together with an alternative PS Candidate (PSC) selection procedure based on the use of pixels classified as urban.
The cases of Caramanico and Volturino are representative, respectively, of harsh and favourable conditions for PSI applications. The results from Caramanico show clusters of PS exhibiting similar line-of-sight (LOS) deformation behaviour in the period 1995–2000. The locations of moving PS often coincide with distressed buildings and appear consistent with the areal distribution of recent and past landslide activity. The temporal displacement trends, however, are characterised by very low annual average velocities (from 3 to 7 mm/y) and it is uncertain to what extent the PS data reflect true slope movements, local deformations (e.g. settlement of engineering structures) or both.
Thanks to the more favourable conditions, the application of the standard SPINUA approach in the Volturino area was sufficient to obtain suitable densities of PS, as well as spatially and temporally consistent displacement results for a period 1992–2000. In particular, a group of moving PS was identified in a peri-urban area, known for the past and recent slope stability problems. The slowly moving PS (from 3 to 5 mm/y) fall in a location that, unlike the remaining part of the town, is characterised by the presence of many distressed buildings and structures. Although the site information confirms the reliability of PS data, in the absence of ground monitoring and detailed records of landslide movements, it is difficult to identify the main mechanism of the detected deformations. In general, in geologically and topographically complex urban/peri-urban settings, the significance of very low-velocity PSI surface displacements should always be considered together with in situ geotechnical controls and ground monitoring data. 相似文献
The reconstruction of digital surface models (DSMs) of urban areas from interferometric synthetic aperture radar (SAR) data is a challenging task. In particular the SAR inherent layover and shadowing effects need to be coped with by sophisticated processing strategies. In this paper, a maximum-likelihood estimation procedure for the reconstruction of DSMs from multi-aspect multi-baseline InSAR imagery is proposed. In this framework, redundant as well as contradicting observations are exploited in a statistically optimal way. The presented method, which is especially suited for single-pass SAR interferometers, is examined using test data consisting of experimental airborne millimeterwave SAR imagery. The achievable accuracy is evaluated by comparison to LiDAR-derived reference data. It is shown that the proposed estimation procedure performs better than a comparable non-statistical reconstruction method. 相似文献
The synthetic fiber ropes such as polyester, aramid and high modulus polyethylene (HMPE) are increasing applied to deepwater mooring systems for oil and gas exploitation. Due to that mooring ropes generally bear tensions for a long period, synthetic fiber ropes that are composed of the viscoelastic material would present creep behaviors and even the creep rupture, which is the failure mode of greatest concern especially for HMPE ropes and on which still less study can be found. A creep damage analysis of synthetic fiber ropes is of necessity to ensure the safe and economic operation of mooring systems. Therefore further investigation on the creep–rupture behavior is beneficial to fully establishing confidence in the viability of synthetic fiber ropes for deepwater moorings. In the present study, a creep–rupture model is proposed within the framework of thermodynamics to investigate the creep and damage behaviors of synthetic fiber ropes. Methods for identifying the model parameters are also proposed in detail, which apply to any component of fiber ropes such as the fiber, yarn, strand and rope. Experimental data of aramid yarns available from the literature are utilized to validate the constitutive model. Creep and creep–rupture tests of HMPE strands at different loading levels are specially performed to further examine the present model. The present work demonstrates that the proposed model can effectively describe the viscoelastic property and damage evolution of synthetic fiber ropes at different loading levels. 相似文献
