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21.
Natural Hazards - Cyclone tracks over the Great Lakes of North America shift, both East–West as well as North–South. The reasons for the shifts are various small-scale as well as... 相似文献
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This study attempts to ascertain the spatial and temporal variations in the evolution of Indian cities using multi-date remote sensing data. A two-stage object-based nearest neighbour classification approach with hierarchical segmentation was used to extract built-up area in selected small, medium and large cities, whereas object-based temporal inversion was applied for change analysis. The temporal trend of net population density, degree of scattered development and compactness of urban core in each city was determined using the built-up area. The study observed a declining trend in growth rate of built-up area in small and medium sized-cities, in contrast to large cities. However, the net population density in cities of all types is decreasing as urban growth has outpaced the corresponding population growth. Furthermore, small and medium cities indicated greater tendency for scattered development in comparison to large cities, whereas the core urban areas of the later appeared relatively less compact. 相似文献
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Performance analysis of different predictive models for crop classification across an aridic to ustic area of Indian states 总被引:1,自引:0,他引:1
The purpose of this study is to present comparative performance analysis of different machine learning algorithms for large area crop classification. Ten Indian districts with significant rabi crops viz. wheat, mustard, gram, red lentils (masoor) have been selected for the study. Most popular classical ensemble models – bagging/ARCing, random forest (RF), gradient boosting and Importance Sampled Learning Ensemble (ISLE) with traditional single model (decision tree) have been selected for comparative analysis. To incorporate dependency of large area crop in different variables viz. parent material and soil, phenology, texture, topography, soil moisture, vegetation, climate etc., 35 digital layers are prepared using different satellite data (ALOS DEM, Landsat-8, MODIS NDVI, RISAT-1, Sentinental-1A) and climatic data (precipitation, temperature). In rabi season, field survey about crop type is carried out to prepare training data. Performance is evaluated on the basis of marginal rates, F-measure and Jaccard’s coefficient of community, Classification Success Index and Agreement Coefficients. Score is calculated to rank the algorithm. RF is best performer followed by gradient boosting for crop classification. Other ensemble methods ARCing, bagging and ISLE are in decreasing order of performance. Traditional non-ensemble method decision tree scored higher than ISLE. 相似文献
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Sarnam Singh T. P. Singh Gaurav Srivastava 《Journal of the Indian Society of Remote Sensing》2005,33(4):547-563
Improving image classification and its techniques have been of interest while handling satellite data especially in hilly
regions with evergreen forests particularly with indistinct ecotones. In the present study an attempt has been made to classify
evergreen forests/vegetation in Moulirig National Park of Arunachal Pradesh in Eastern Himalayas using conventional unsupervised
classification algorithms in conjunction with DEM. The study area represents climax vegetation and can be broadly classified
into tropical, subtropical, temperate and sub-alpine forests. Vegetation pattern in the study area is influenced strongly
by altitude, slope, aspect and other climatic factors. The forests are mature, undisturbed and intermixed with close canopy.
Rugged terrain and elevation also affect the reflectance. Because of these discrimination among the various forest/vegetation
types is restrained on satellite data. Therefore, satellite data in optical region have limitations in pattern recognition
due to similarity in spectral response caused by several factors. Since vegetation is controlled by elevation among other
factors, digital elevation model (DEM) was integrated with the LISS III multiband data. The overall accuracy improved from
40.81 to 83.67%. Maximum-forested area (252.80 km2) in national park is covered by sub-tropical evergreen forest followed
by temperate broad-leaved forest (147.09 km2). This is probably first attempt where detailed survey of remote and inhospitable areas of Semang sub-watershed, in and around
western part of Mouling Peak and adjacent areas above Bomdo-Egum and Ramsingh from eastern and southern side have been accessed
for detailed ground truth collection for vegetation mapping (on 1:50,000 scale) and characterization. The occurrence of temperate
conifer forests and Rhododendron Scrub in this region is reported here for the first time. The approach of DEM integrated
with satellite data can be useful for vegetation and land cover mapping in rugged terrains like in Himalayas. 相似文献
26.
Gaurav J. Kokandakar Sachin S. Ghodke K. Rathna Laxman B. More B. Nagaraju Munjaji V. Bhosle K. Vijaya Kumar 《Journal of the Geological Society of India》2018,91(2):135-146
Three distinct alkaline magmas, represented by shonkinite, lamprophyre and alkali basalt dykes, characterize a significant magmatic expression of rift-related mantle-derived igneous activity in the Mesoproterozoic Prakasam Alkaline Province, SE India. In the present study we have estimated emplacement velocities (ascent rates) for these three varied alkaline magmas and compared with other silicate magmas to explore composition control on the ascent rates. The alkaline dykes have variable widths and lengths with none of the dykes wider than 1 m. The shonkinites are fine- to medium-grained rocks with clinopyroxene, phologopite, amphibole, K-feldspar perthite and nepheline as essential minerals. They exhibit equigranular hypidiomorphic to foliated textures. Lamprophyres and alkali basalts characteristically show porphyritic textures. Olivine, clinopyroxene, amphibole and biotite are distinct phenocrysts in lamprophyres whereas olivine, clinopyroxene and plagioclase form the phenocrystic mineralogy in the alkali basalts. The calculated densities [2.54–2.71 g/cc for shonkinite; 2.61–2.78 g/cc for lamprophyre; 2.66–2.74 g/cc for alkali basalt] and viscosities [3.11–3.39 Pa s for shonkinite; 3.01–3.28 Pa s for lamprophyre; 2.72–3.09 Pa s for alkali basalt] are utilized to compute velocities (ascent rates) of the three alkaline magmas. Since the lamprophyres and alkali basalts are crystal-laden, we have also calculated effective viscosities to infer crystal control on the velocities. Twenty percent of crystals in the magma increase the viscosity by 2.7 times consequently decrease ascent rate by 2.7 times compared to the crystal-free magmas. The computed ascent rates range from 0.11–2.13 m/sec, 0.23–2.77 m/sec and 1.16–2.89 m/sec for shonkinite, lamprophyre and alkali basalt magmas respectively. Ascent rates increase with the width of the dykes and density difference, and decrease with magma viscosity and proportion of crystals. If a constant width of 1 m is assumed in the magma-filled dyke propagation model, then the sequence of emplacement velocities in the decreasing order is alkaline magmas (4.68–15.31 m/sec) > ultramafic-mafic magmas (3.81–4.30 m/sec) > intermediate-felsic magmas (1.76–2.56 m/sec). We propose that SiO2 content in the terrestrial magmas can be modeled as a semi-quantitative “geospeedometer” of the magma ascent rates. 相似文献
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Kanika Sharma Arun K. Saraf Josodhir Das Suman S. Baral Susanta Borgohain Gaurav Singh 《Journal of the Indian Society of Remote Sensing》2018,46(4):605-615
The devastating earthquake that struck Nepal in 25 April (Mw7.8) and 12 May (Mw7.3) 2015 have triggered numerous landslides and reactivated existing landslides extending over large areas. These two shocks mostly affected the northwest and northeast region of Kathmandu which accelerated large region along with southward up thrusting in the region. To detect the event of the landslides in time and space satellite images have been analysed using space remote sensing techniques like pseudo colour transformation technique and was employed to pre and post-earthquake images of the event to bring out only landslide affected areas from the image by masking the remaining part, where field based survey of the landslides provided information on real nature of it, slope and rock type. Surprisingly the observed mass movements are mostly belong to debris flow and rock fall types beginning from the top part of the ridge slope with south-westerly faces i.e. sun facing. Further, satellite images of different dates could be gathered which facilitated analysis on development of landslide with time. This study also revealed that the NE–SW trending geological faults have controlled the landslide occurrence especially in Ramche area and along the Bagmati river valley near Shital-chowk village on Kathmandu-Hetauda road. 相似文献
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Surajit Misra Sukanta Roy Vikrant Bartakke Gaurav Athavale Harsh Gupta 《Journal of the Geological Society of India》2017,89(2):131-132
Mn-rich ilmenites (up to 7 % MnO) have been identified in dykes cutting the Malanjkhand porphyry copper mining area in Madhya Pradesh. The dykes are hydrothermally altered and are of tholeiitic affinities. Lamprophyres have been reported from nearby areas. The presence of Mn-rich Ilmenites in the Malanjkhand copper mine dykes and the occurrence of lamprophyres and the pervasive potassium metasomatism in the area strongly suggests a possibility of finding diamondiferous rocks in the area. Such high-Mn bearing ilmenites are associated with diamondiferous deposits in other parts of the world, e.g. Juina kimberlites, Brazil. Mn-bearing ilmenite is considered as an indicator mineral for kimberlite/diamond occurrences. The presence of kimberlite pipes in Raipur district and the association of Mn-rich ilmenite with kimberlites is a fortuitous coincidence for venture-some mining companies. A probable explanation for the origin of manganese layers in the context of ‘rift’ tectonic environment is offered. Also a possible link between the dykes, quartz veins in the Malanjkhand granitic rocks and the copper mineralization is proposed. 相似文献
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Sub‐sample time shift and horizontal displacement measurements using phase‐correlation method in time‐lapse seismic 下载免费PDF全文
Hydrocarbon production and fluid injection affect the level of subsurface stress and physical properties of the subsurface, and can cause reservoir‐related issues, such as compaction and subsidence. Monitoring of oil and gas reservoirs is therefore crucial. Time‐lapse seismic is used to monitor reservoirs and provide evidence of saturation and pressure changes within the reservoir. However, relative to background velocities and reflector depths, the time‐lapse changes in velocity and geomechanical properties are typically small between consecutive surveys. These changes can be measured by using apparent displacement between migrated images obtained from recorded data of multiple time‐lapse surveys. Apparent displacement measurements by using the classical cross‐correlation method are poorly resolved. Here, we propose the use of a phase‐correlation method, which has been developed in satellite imaging for sub‐pixel registration of the images, to overcome the limitations of cross‐correlation. Phase correlation provides both vertical and horizontal displacements with a much better resolution. After testing the method on synthetic data, we apply it to a real dataset from the Norne oil field and show that the phase‐correlation method can indeed provide better resolution. 相似文献
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Amar Agarwal K K Agarwal R Bali Chandra Prakash Gaurav Joshi 《Journal of Earth System Science》2016,125(4):873-884
The present study aims to understand evolution of the Lesser Himalaya, which consists of (meta) sedimentary and crystalline rocks. Field studies, microscopic and rock magnetic investigations have been carried out on the rocks near the South Almora Thrust (SAT) and the North Almora Thrust (NAT), which separates the Almora Crystalline Zone (ACZ) from the Lesser Himalayan sequences (LHS). The results show that along the South Almora Thrust, the deformation is persistent; however, near the NAT deformation pattern is complex and implies overprinting of original shear sense by a younger deformational event. We attribute this overprinting to late stage back-thrusting along NAT, active after the emplacement of ACZ. During this late stage back-thrusting, rocks of the ACZ and LHS were coupled. Back-thrusts originated below the Lesser Himalayan rocks, probably from the Main Boundary Thrust, and propagated across the sedimentary and crystalline rocks. This study provides new results from multiple investigations, and enhances our understanding of the evolution of the ACZ. 相似文献