Abstract: Atmospheric aerosols have constituted a crucial environmental and climate issue. There is lack of studies dealing with monitoring of aerosol patterns over Bangladesh. This review attempts to analyze the seasonal variations in AOD over Bangladesh during the period 2002-2011, using MODerate resolution Imaging Spectroradiometer (MODIS) Level 3 remote sensing data. A Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model is used to generate a backward trajectory in order to identify the origins of air masses, with the aim of understanding the spatio-temporal variability in aerosol concentration. Seasonal variations during the last decade show maximum AOD values during pre-monsoon season; while minimum AOD during post-monsoon. An evidence of decadal decreasing trend in AOD is found during monsoon season while all other seasons show increasing trends. High spatio-temporal variations of AOD are observed during different seasons in 2010. Back trajectory analysis indicates that Bangladesh is mainly affected by the pollutants and desert dust of India combining with sea salt particles blown from the Arabian Sea. The air masses are arriving at lower altitudes (500m, 1500m) mainly from western India and Indian subcontinent but at higher altitude (2500m) especially in winter season it comes from far western regions, such as Europe and various sub-Saharan regions of Africa. Different flow patterns of air masses during post-monsoon are observed that the air masses are arriving from southeast in the direction; in case of Sylhet division the sources of air masses are in the coastal regions of Thailand, border regions of Myanmar and China. These studies become helpful to understand the nature and influence of aerosols on seasonal dynamics over Bangladesh.Abstract: Atmospheric aerosols have constituted a crucial environmental and climate issue. There is lack of studies dealing with monitoring of aerosol patterns over Bangladesh. This review attempts to analyze the seasonal variations in AOD over Bangladesh during the period 2002-2011, using MODerate resolution Imaging Spectroradiometer (MODIS) Level 3 remote ...Show More
Abstract: Deterioration and aging of bridges structures and damage caused by strong earthquakes might be conducive to collapse of the bridge, sometimes with catastrophic consequences. Therefore, investigation of structural condition of bridges is necessary for secure safe road operations. This paper presents a prototype of piezoelectric-cable sensor for vibration monitoring system that permits easy evaluation of the bridge structure integrity. For this study, a bridge located at Yurihonjo city, Japan was chosen as a target structure. The structure is a continuous beam type bridge with steel beams of various sections and lengths and reinforced concrete slabs to support the asphalt carpet. The bridge comprises seven spans with total length of 256 m. Experimental measurements were taken of the first span near the left abutment. Quantitatively, the natural period of vibration is obtainable from signals recorded using the proposed data acquisition system. Subsequently, results obtained from the proposed system are compared with those obtained from common accelerometers. A piezoelectric sensor emits a signal when a change in the stress condition occurs. Therefore, the sensor was set up at the support of the bridge where large changes in the stress level are expected to occur. The target bridge was also subjected to moving loads. Its vibration response was also obtained. The experiment was performed using a track of 19 t of equivalent weight. Responses were captured appropriately using the proposed system. They are comparable to responses obtained using accelerometers. Although the general response pattern is obtained appropriately, it is necessary to improve the accuracy of the proposed system to gather more reliable data. As presented herein, the general outline of the proposed system is described, mentioning the main specifications and assessing possible means to improve the data acquisition system to permit stable and accurate monitoring of bridge structures.Abstract: Deterioration and aging of bridges structures and damage caused by strong earthquakes might be conducive to collapse of the bridge, sometimes with catastrophic consequences. Therefore, investigation of structural condition of bridges is necessary for secure safe road operations. This paper presents a prototype of piezoelectric-cable sensor for vibr...Show More
