1,720,980 research outputs found
Land-cover classification-based persistent scatterers identification for peri-urban applications
No full textWe illustrate, through a sample application to a difficult landslide test site, the use of a novel method to detect potentially stable objects in Persistent Scatterers SAR Interferometry (PSI). Conventional PSI processing involves selecting first-guess potential stable objects, called PS Candidates (PSC), through thresholding of the amplitude dispersion index. This method can lead, in applications to scenes characterized by scarce urbanization, to very low PSC numbers, insufficient for a successful subsequent phase analysis if their spatial distribution is very sparse. Our classification-based approach relies on the proven fact that urban areas are more likely to contain PS pixels than any other land-cover class. Therefore, using pixels belonging to the urban land-cover class as PSC is a convenient way of increasing the number of initial fiducial points while keeping false alarm probabilities to reasonable levels. Results show that PSC belonging to the urban class, selected through simple external classification algorithms, lead to more consistent results for the final PS, both in terms of spatial density, and of reliability of displacement series
Phase unwrapping as an ill-posed problem: Performance comparison between a neural network based approach and a stochastic search method
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Retrieval chlorophyll-a concentration in the Taranto coastal area using remote sensed data
No full textMonitoring of coastal waters for an early detection of pollution and eutrophication phenomena related to urban settlements and industrial activities is becoming of increasing importance for environmental protection and disaster prevention. For this purpose, high resolution, multi-spectral satellite data have been successfully applied in the detection of chemical, biological and physical processes developing in coastal waters, but they appear to be heavily penalized in the study of fast dynamical phenomena, due to their typically long revisiting time. At the same time, datasets from satellites for atmospheric and oceanic applications do have an appropriate revisiting time and an excellent spectral resolution, but generally are not considered suitable for coastal water studies, given their limited spatial resolution. In this paper, we present a preliminary evaluation of the utilization of oceanic sensors in the monitoring of coastal shallow waters. Among other parameters, we have measured the Chlorophyll-a concentration in the Taranto coastal waters, utilizing SeaWifS (SeaWide Field-of-view Sensor) data, as part of the SPICAMAR experiment conducted by environmental specialists, who have provided a very complete dataset relative to the ground (sea) truth. The "Tarante Seas" are three small water basins, nearly closed, with a total extension of about 55 km2 and a small depth (7 m., 10 m. and 20 m. average depth respectively), located in southern Italy on the Ionian sea, very close to a large town and an important industrial settlement. Due to the low extension of the area of interest an important source of errors derived from pixels marginally contaminated by coastal land reflectivity. This effect has been partially eliminated trough a very accurate geo - .referencing and selection of each single pixel to be used for the evaluation. A radiative transfer code has been used to remove the atmospheric effect by SeaWiFS image. To retrieval chlorophyll concentration we have implemented a semianalytic algorithms. The performance of these procedure and algorithms are presented to show the potential use and the limits of oceanic sensors for coastal waters monitoring
Using multi-temporal interferometry and Sentinel-1 data to monitor ground instability hazards related to open-cast mining operations
No full textSurface mining represents the predominant mineral and coal exploitation method in Europe and worldwide. Different mining methods can be involved, but most often: open-cast (open-pit) mining; terrace mining; contour strip mining; quarrying. Although surface mining is considered safer than underground mining, ground instability hazards represent an ever-present concern and important problem limiting the mining operations (e.g., slope instability in high wall open-cast mines and quarries). However, given the often large extent of areas affected by surface mining and life span of mines (tens of years), long-term monitoring via traditional in-situ methods is typically impractical (economically and technically). Here we focus on the use of an advanced multi-temporal interferomery (MTI) and Sentinel-1 imagery for mapping and monitoring of ground instabilities in open-cast mines and adjacent areas. Open-cast mines represent a good target for MTI, because they are i) often very large (from few to tens of km2); ii) free of or covered by sparse vegetation; iii) require long-term regular monitoring, which can now rely on free of charge Sentinel-1 data from the European Space Agency. However, a cursory review of the recent literature (international journals) suggests that in comparison to applications to underground mines, MTI has been relatively little exploited to investigate ground instabilities related to surface mining. One reason for this is that some portions of open-cast mines can lack measurable radar targets due to rapid changes of ground surface caused by intense mining operations (e.g., overburden stripping, waste material damping). We argue that this limitation can now be mitigated by the higher frequency and regularity of acquisitions provided by Sentinel-1 (nominally every 6 days since October 2016). To illustrate the potential of MTI for detecting and monitoring ground instabilities induced by surface mining, we present case study example of the Belchatow mine (Poland), one of the largest brown coal open-cast operations in Europe (about 12 km long and 3 km wide). The Belchatow open-cast mine reaches the depth of 310 m and has been affected by a number of slope failures in the last few decades. The failures disrupted the mining operations, destroyed in part the mining machinery and resulted in high economic losses. In this study we assess the recent and current stability conditions in the mine area by exploiting several tens of medium resolution (~20 m) images acquired by Sentinel-1 since October 2014. Despite the local lack of information (areas affected by intensive surface disturbance due to ongoing mining operations), the MTI results provided a valuable synoptic overview of the ground instability/stability condition within and outside the active mine. Although it is not simple to provide short-term forewarning of the impeding slope failure on the basis of the surface displacement time series alone, our experience indicate that long-term, high frequency MTI measurements offer the following benefits: i) better anticipation of risk of failure over large areas and more rational design of ground-based monitoring networks; ii) better planning for maintenance and management of open-cast mines
High resolution satellite multi-temporal interferometry for monitoring infrastructure instability hazards
No full textAdvanced remote sensing techniques are now capable of delivering more rapidly high quality information that is sufficiently detailed (and cost-effective) for many engineering applications. Here we focus on synthetic aperture radar (SAR), multi-temporal interferometry (MTI). With radar satellites periodically re-visiting the same area, MTI provides information on distance changes between the on-board radar sensor and the targets on the ground (e.g., human-made structures such as buildings, roads and other infrastructure). The detected distance changes are thus interpreted as evidence of ground and/or structure instability. In settings with limited vegetation cover, MTI can deliver very precise (mm resolution), spatially dense information (from hundreds to thousands measurement points/km 2) on slow (mm-cm/year) deformations affecting the ground and engineering structures. Radar satellites offer wide-area coverage (thousands km 2) and, with the sensors that actively emit electromagnetic radiation and thus can "see'' through the clouds, one can obtain deformation measurements even under bad weather conditions. We illustrate the potential of high resolution MTI and explain what this technique can deliver to assist in infrastructure instability hazard assessment. This is done by presenting selected examples of MTI applied to monitor post-construction behavior of engineering structures. The examples are from Italy and include: an earthfill dam, an off-shore vertical breakwater built to protect an oil terminal, city buildings and a highway. We also stress that the current approach to the assessment of instability hazard can be transformed by capitalizing more on the presently underexploited advantage of the MTI technique, i.e., the capability to provide regularly spatially dense quantitative information for large areas where engineering infrastructure may currently be unaffected by instability, but where the terrain and infrastructure history (e.g., aging) may indicate potential for future failures
Feasibility of Using Synthetic Aperture Radar to Aid UAV Navigation
Full text linkThis study explores the potential of Synthetic Aperture Radar (SAR) to aid Unmanned Aerial Vehicle (UAV) navigation when Inertial Navigation System (INS) measurements are not accurate enough to eliminate drifts from a planned trajectory. This problem can affect medium-altitude long-endurance (MALE) UAV class, which permits heavy and wide payloads (as required by SAR) and flights for thousands of kilometres accumulating large drifts. The basic idea is to infer position and attitude of an aerial platform by inspecting both amplitude and phase of SAR images acquired onboard. For the amplitude-based approach, the system navigation corrections are obtained by matching the actual coordinates of ground landmarks with those automatically extracted from the SAR image. When the use of SAR amplitude is unfeasible, the phase content can be exploited through SAR interferometry by using a reference Digital Terrain Model (DTM). A feasibility analysis was carried out to derive system requirements by exploring both radiometric and geometric parameters of the acquisition setting. We showed that MALE UAV, specific commercial navigation sensors and SAR systems, typical landmark position accuracy and classes, and available DTMs lead to estimated UAV coordinates with errors bounded within ±12 m, thus making feasible the proposed SAR-based backup system
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