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排序方式: 共有139条查询结果,搜索用时 15 毫秒
101.
Dynamics of land use/cover changes and the analysis of landscape fragmentation in Dhaka Metropolitan, Bangladesh 总被引:3,自引:0,他引:3
Rapid urban expansion due to large scale land use/cover change, particularly in developing countries becomes a matter of concern since urbanization drives environmental change at multiple scales. Dhaka, the capital of Bangladesh, has been experienced break-neck urban growth in the last few decades that resulted many adverse impacts on the environment. This paper was an attempt to document spatio-temporal pattern of land use/cover changes, and to quantify the landscape structures in Dhaka Metropolitan of Bangladesh. Using multi-temporal remotely sensed data with GIS, dynamics of land use/cover changes was evaluated and a transition matrix was computed to understand the rate and pattern of land use/cover change. Derived land use statistics subsequently integrated with landscape metrics to determine the impact of land use change on landscape fragmentation. Significant changes in land use/cover were noticed in Dhaka over the study period, 1975–2005. Rapid urbanization was manifested by a large reduction of agricultural land since urban built-up area increased from 5,500?ha in 1975 to 20,549?ha in 2005. At the same time, cultivated land decreased from 12,040 to 6,236?ha in the same period. Likewise, wetland and vegetation cover reduced to about 6,027 and 2,812?ha, respectively. Consequently, sharp changes in landscape pattern and composition were observed. The landscape became highly fragmented as a result of rapid increase in the built-up areas. The analysis revealed that mean patch size decreased while the number of patches increased. Landscape diversity declined, urban dominance amplified, and the overall landscape mosaics became more continuous, homogenous and clumped. In order to devise sustainable land use planning and to determine future landscape changes for sound resource management strategies, the present study is expected to have significant implications in rapidly urbanizing cities of the world in delivering baseline information about long term land use change and its impact on landscape structure. 相似文献
102.
Abel inversion for deriving refractivity profile from down-looking GPS radio occultation: simulation analysis 总被引:1,自引:1,他引:0
Down-looking (DL) Global Positioning System (GPS) radio occultation can produce an estimate of the atmospheric refractivity profile. The main observations are the bending angle as a function of the impact parameter. DL provides both negative as well as positive elevation angle measurements. Abel inversion can be operated on a profile of partial bending angle found by subtracting the positive elevation measurement from the negative one with the same impact parameter. Abel inversion requires the spherical symmetrical assumption. Basically, partial bending calculation removes the ionospheric bending and hence it is possible to use a single frequency GPS receiver. The current paper introduces a simulation data for the case of a receiver on mountain top. The simulation uses model refractivity from MSISE-90 model as well as radiosonde data. Random noises are added to the bending angle profile before inversion. The result shows that it is possible to produce accurate vertical refractivity profile below the receiver altitude. The calculation of the water vapor profile is also made using temperature profile information from the MSISE-90 model as well as radiosonde. The errors in the retrieved vapor profile are always less than 0.1?mbar. 相似文献
103.
Ashraf Latif Tadross 《New Astronomy》2012,17(2):198-202
We present here the astrophysical parameters of three stellar open cluster candidates using PPMXL (<http://vizer.cfa.harvard.edu/viz-bin/VizieR?-source=I/317>) database. In this study, the main photometric, astrometry and statistical parameters of Ruprecht 13, Ruprecht 16 and Ruprecht 24 are estimated for the first time. 相似文献
104.
Ashraf Farahat 《Journal of Astrophysics and Astronomy》2010,31(2):81-88
A new numerical model of particle propagation in the Galaxy has been developed, which allows the study of cosmic-ray production
and propagation in 2D. The model has been used to solve cosmic ray diffusive transport equation with a complete network of
nuclear interactions using the time backward Markov stochastic process by tracing the particles’ trajectories starting from
the Solar System back to their sources in the Galaxy. This paper describes a further development of the model to calculate
the contribution of various galactic locations to the production of certain cosmic ray nuclei observed at the Solar System. 相似文献
105.
Salman Ashraf Lars BrabynBrendan J. Hicks 《Applied geography (Sevenoaks, England)》2012,32(2):619-628
Remote sensing based mapping of diverse and heterogeneous freshwater environments requires high-resolution images. Data fusion is a useful technique for producing a high-resolution multispectral image from the merging of a high-resolution panchromatic image with a low-resolution multispectral image. Given the increasing availability of images from different satellite sensors that have different spectral and spatial resolutions, data fusion techniques that combine the strengths of different images will be increasingly important to Geography for land-cover mapping. Different data fusion methods however, add spectral and spatial distortions to the resultant data depending on the geographical context; therefore a careful selection of the fusion method is required. This paper compares a technique called subtractive resolution merge, which has not previously been formally tested, with conventional techniques such as Brovey transformation, principal component substitution, local mean and variance matching, and optimised high pass filter addition. Data fusion techniques are grouped into spectral and spatial centric methods. Subtractive resolution merge belongs to a new class of data fusion techniques that uses a mix of both spatial and spectral centric approaches. The different data fusion techniques were applied to a QuickBird image of a semi-aquatic freshwater environment in New Zealand. The results were compared both qualitatively and quantitatively using spectral and spatial error metrics. This research concludes that subtractive resolution merge performed better than all the other techniques and will be a valuable technique for enhancing images for freshwater land-cover mapping. 相似文献
106.
Kafeel Ahmad Zafar Iqbal Khan Asma Ashfaq Muhammad Ashraf Nudrat Aisha Akram Muhammad Sher Hazoor Ahmad Shad Vincenzo Tufarelli Antonio Lonigro Mariano Fracchiolla Eugenio Cazzato 《Environmental Earth Sciences》2017,76(8):322
Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg?1 for Mo, 2.77–4.28 mg kg?1 for As, 0.395–0.705 mg kg?1 for Se, 36.73–48.17 mg kg?1 for Fe, 10.58–16.26 mg kg?1 for Cu, 28.87–39.79 mg kg?1 for Zn, 6.66–8.75 mg kg?1 for Ni and 4.33–6.09 mg kg?1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals. 相似文献
107.
The present study was aimed at assessing the groundwater contamination from arsenic (As) and its impact on health from survey data in Lahore, Pakistan. OK (ordinary kriging) technique was used to create As and pH surfaces for samples from 380 groundwater wells at different locations and depths in the study area. Geographic information systems (GIS) was applied to delineate areas for safe, risk, and dangerous zones of As in drinking water from groundwater wells at 640 to 850 ft depths. To analyze effects of high As on public health, GIS-based field surveys were conducted to link health data along location of respondents to As contamination levels in the delineated safe, risk, and dangerous zones. Moreover, various pH levels and their effectiveness were studied to suggest cost-effective As treatment in the study area. Our results show that As contaminated strata varies with depth of groundwater wells, i.e., 44.50% areas comprising safe zone of drinking water from deep wells at 850 ft depth compared to 26% areas of shallow water at 640 ft depth. About 35% area with pH range (7 to 7.5) is marked in the risk and danger zones of As that can be initially targeted for treatment. Surveys confirm that people living in the risk and danger zones have some kind of As-related diseases. 相似文献
108.
Ashraf Adly Laurentiu Danciu Donat Fäh Valerio Poggi Awad Omran Awad Hassoup 《Bulletin of Earthquake Engineering》2018,16(12):5697-5733
A new seismic hazard model for Cairo, the capital city of Egypt is developed herein based on comprehensive consideration of uncertainties in various components of the probabilistic seismic hazard analysis. The proposed seismic hazard model is developed from an updated catalogue of historical and instrumental seismicity, geodetic strain rates derived from GPS-based velocity-field of the crust, and the geologic slip rates of active faults. The seismic source model consists of area sources and active faults characterised to forecast the seismic productivity in the region. Ground motion prediction models are selected to describe the expected ground motion at the sites of interest. The model accounts for inherent epistemic uncertainties of statistical earthquake recurrence; maximum magnitude; ground motion prediction models, and their propagation toward the obtained results. The proposed model is applied to a site-specific hazard analysis for Kottamiya, Rehab City and Zahraa-Madinat-Nasr (hereinafter referred to as Zahraa) to the East of Cairo (Egypt). The site-specific analysis accounts for the site response, through the parameterization of the sites in terms of average 30-m shear-wave velocity (Vs30). The present seismic hazard model can be considered as a reference model for earthquake risk mitigation and proper resilience planning. 相似文献
109.
Alamgir Mahiuddin Khan Najeebullah Shahid Shamsuddin Yaseen Zaher Mundher Dewan Ashraf Hassan Quazi Rasheed Balach 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(2):447-464
Stochastic Environmental Research and Risk Assessment - Drought is considered to be one of the most devastating natural hazards, causing widespread environmental and social damage in many parts of... 相似文献
110.
SUN Ge SUN Chunlin SUN Yuewu ZHANG Shuqin WU Wenhao YANG Tao LIANG Fei FENG Yuhui Markevich V Ashraf A R Bugdaeva E Tekleva M Suzuki S 《世界地质(英文版)》2021,24(4):189-197
The non-marine Cretaceous-Paleogene boundary ( KPgB) in Jiayin of Heilongjiang was first defined and reported in China by the authors' research team in 2011 . Thereafter the continuous research on the KPgB and its related Late Cretaceous biota in Jiayin has been made by the authors in 2012-2020 . The achievements of the research are mainly reflected as follows:(1) a new drilling borehole with 60 m in depth carried out in the Xiaoheyan of Jiayin in 2016 , supplemented new palynological evidence for the KPgB definition in 2011;( 2 ) some radiometric dating newly made on the strata related to the KPgB in Jiayin and its neighboring Russian area, provided the supplemental evidence for the KPgB definition in Jiayin;( 3 ) many new fossils found by the au-thors, represented by the angiosperms Dalembia and Nelumbo, refresh understanding the Late Cretaceous envi-ronment of Jiayin;and (4) the TEM method is applied in the study of pollen exine ultrastructure of Pseudoin-tegricorpus, Wodehouseia, and Aquilapollenites, promoting the late Maastrichtian ecological study in Jiayin, re-lated to the KPgB. 相似文献