Improving the assessment of ICESat water altimetry accuracy accounting for autocorrelation     

Hani Abdallah  Jean-Stéphane Bailly  Nicolas Baghdadi  Nicolas Lemarquand 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):833-844

Given that water resources are scarce and are strained by competing demands, it has become crucial to develop and improve techniques to observe the temporal and spatial variations in the inland water volume. Due to the lack of data and the heterogeneity of water level stations, remote sensing, and especially altimetry from space, appear as complementary techniques for water level monitoring. In addition to spatial resolution and sampling rates in space or time, one of the most relevant criteria for satellite altimetry on inland water is the accuracy of the elevation data. Here, the accuracy of ICESat LIDAR altimetry product is assessed over the Great Lakes in North America. The accuracy assessment method used in this paper emphasizes on autocorrelation in high temporal frequency ICESat measurements. It also considers uncertainties resulting from both in situ lake level reference data. A probabilistic upscaling process was developed. This process is based on several successive ICESat shots averaged in a spatial transect accounting for autocorrelation between successive shots. The method also applies pre-processing of the ICESat data with saturation correction of ICESat waveforms, spatial filtering to avoid measurement disturbance from the land–water transition effects on waveform saturation and data selection to avoid trends in water elevations across space. Initially this paper analyzes 237 collected ICESat transects, consistent with the available hydrometric ground stations for four of the Great Lakes. By adapting a geostatistical framework, a high frequency autocorrelation between successive shot elevation values was observed and then modeled for 45% of the 237 transects. The modeled autocorrelation was therefore used to estimate water elevations at the transect scale and the resulting uncertainty for the 117 transects without trend. This uncertainty was 8 times greater than the usual computed uncertainty, when no temporal correlation is taken into account. This temporal correlation, corresponding to approximately 11 consecutive ICESat shots, could be linked to low transmitted ICESat GLAS energy and to poor weather conditions. Assuming Gaussian uncertainties for both reference data and ICESat data upscaled at the transect scale, we derived GLAS deviations statistics by averaging the results at station and lake scales. An overall bias of −4.6 cm (underestimation) and an overall standard deviation of 11.6 cm were computed for all lakes. Results demonstrated the relevance of taking autocorrelation into account in satellite data uncertainty assesment.  相似文献   

RC structures cyclic behavior simulation with a model integrating plasticity,damage, and bond‐slip          下载免费PDF全文

Bashar Alfarah  Juan Murcia‐Delso  Francisco López‐Almansa  Sergio Oller 《地震工程与结构动力学》2018,47(2):460-478

The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics‐based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond‐slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond‐slip of 2 or more crossing reinforcing bars in beam‐column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond‐slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation.  相似文献   

GIS-based multi-criteria land suitability analysis for sustainable agriculture in the northeast area of Tadla plain (Morocco)     

Widad Ennaji  Ahmed Barakat  Mohamed El Baghdadi  Hakima Oumenskou  Mohamed Aadraoui  Lalla Aicha Karroum  Abdessamad Hilali 《Journal of Earth System Science》2018,127(6):79

Assessment of soil suitability for sustainable intensive agriculture is an appropriate tool to select the land suitable for agricultural production with the least economic and environmental costs. This study was conducted to evaluate the agricultural soil quality in the northeast area of Tadla plain (Morocco) using geographic information system (GIS) and analytical hierarchy process (AHP). Six soil quality indicators, i.e., pH, organic carbon, cation exchange capacity, texture, salinity and slope were considered and performed in 60 subsurface soil samples. AHP method was utilized to identify the weight of each indicator from the pairwise comparison matrix. The weighted sum overlay analysis was then used to generate the soil quality map in a GIS environment, by overlaying both indicator weights and sub-indicator weights. The studied area was classified into four soil quality categories, i.e., poor, medium, good, and excellent, the percentage of each category is 1.12, 20.98, 61.07 and 16.83%, respectively. The results indicated that 1.12% of the study area has poor suitability for sustainable intensive agriculture due to their unsuitable texture and low salinity, while about 77% of cultivated soils are adapted to agricultural production. The above results could be useful for the management of agricultural activity.  相似文献   

Probing the lethal agent in the hot spring of the Death Valley in Tashan,south of Iran     

R. F. Motlagh  J. Valiallahi  M. Baghdadi 《International Journal of Environmental Science and Technology》2018,15(7):1573-1580

Death Valley located in the Zagros Mountains, Khuzestan Province, Iran, along the Bangeston Fault line is a unique landscape. Water flows from a hot headstream through a colorful bed into the valley for about 2 km down-run and disappears through the alluvial deposits. This spring and its surrounding area were found to be deadly for both animals and humans. In the last decade, it has been reported that five persons and many animals have died. The reason for the toxicity of this water has not yet been specified. Attempts have been made to find out the secret behind death. The purpose of this paper is to study the Death Valley, which is located in the south of Iran (Tashan), as well as the lethal agent and other index mineral compounds in its water. Air analysis was performed near the headstream to find more about the fatal gas in the area. The results showed that the concentration of hydrogen sulfide was as high as 400 ppm near the spring during hot season, which could lead to pulmonary edema and death. Water in the area contains a high concentration of sulfide (1780 mg/L), which is a characteristic of thermal or hot spring waters. This gas is available along the stream and also far from the spring. The amount of spring water is high enough to be exploited for remedial purposes.  相似文献   

Heavy metal pollution and soil magnetic susceptibility in urban soil of Beni Mellal City (Morocco)   总被引：3，自引：2，他引：1  

Mohamed El Baghdadi  Ahmed Barakat  Mohamed Sajieddine  Samir Nadem 《Environmental Earth Sciences》2012,66(1):141-155

The assessment of anthropogenic impact in the urban environment can be evaluated according to heavy metal contents of soils such as Pb, Cu, Zn, Cd and Fe. These elements have more affinity to establish metallic bond with ferrous material leading to enhancement of soil magnetic susceptibility. The objective of this study was to undertake joint magnetic and geochemical investigations of road-side urban soil materials to address the environmental pollution of Beni Mellal city that has been subjected to environmental stress, due to population overpressure and related urbanization. Twenty three soils magnetic susceptibility profiles were made along 5 km peripheral national road (N8) in Beni Mellal. The magnetic survey reported here for the first time on this City’s topsoils tries to establish the link between magnetic properties and the content of heavy metals. High magnetic susceptibility values and high contents of heavy metals were found near the paved edge of the road and within the place reserved as large engine park. Magnetic extracts of highly polluted areas and unpolluted soil (olive plantation) were analyzed by SEM coupled with RDX in order to discriminate anthropogenic magnetic spherules and pedo-lithogenic magnetite-like minerals. Magnetic mineralogy determined by Mössbauer spectroscopy suggests the presence of hematite, magnetite and goethite in highly polluted areas. The iron oxides and especially goethite are efficient in incorporating and/or adsorbing foreign ions.  相似文献   

Measuring coseismic deformation on the northern segment of the Bam-Baravat escarpment associated with the 2003 Bam (Iran) earthquake, by correlation of very-high-resolution satellite imagery     

M. de Michele  D. Raucoules  H. Aochi  N. Baghdadi  C. Carnec 《Geophysical Journal International》2008,173(2):459-464

  相似文献   

Indicators of Chemical Pollution from Septic Systems   总被引：5，自引：0，他引：5  

Bashar J. Alhajjar  Gordon Chesters  John M. Harkin 《Ground water》1990,28(4):559-568

  相似文献