Early In-orbit Performance of Scanning Sky Monitor Onboard AstroSat

We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ \(\times \) 2.5\(^\circ \) and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.     

Patterns of carbon sequestration in forests of western ghats and study of applicability of remote sensing in generating carbon credits through afforestation/reforestation

Satellite remote sensing is a proven tool for mapping landuse patterns and estimating vegetation biomass/carbon. Present study aims at estimating the potential of forests of Radhanagari WLS (Western Ghats, India) to sequester the atmospheric carbon-di-oxide, using ground based observations coupled with satellite remote sensing. The study area was stratified for dominant forest types based on the structure and composition of vegetation and elevation variations. Permanent sample plots were laid down in these homogeneous vegetation strata (HVS) to make different observations during time 1 and time 2. Carbon sequestration by plantations was also studied and compared with natural forests. Species and area-specific biomass equations were used for estimating carbon pool and sequestration. Among natural forests ‘mixed moist deciduous’ forests exhibited highest sequestration rate (8%), whereas, plantation as obvious had a comparatively higher sequestration rate than natural forests (20.27%). Total carbon sequestration by forests of the Radhanagari WLS between 2004 and 2006 is 78742.09 tons. Eligible land for reforestation activity under clean development mechanism (CDM) of Kyoto Protocol was identified using satellite remote sensing using 1989 and 2005 datasets and it was observed that the potential land that can be used for reforestation activity is 10080 ha.     

Assessment of groundwater potential zones using GIS technique

A case study was conducted to find out the groundwater potential zones in Kattakulathur block, Tamil Nadu, India with an aerial extent of 360.60 km². The thematic maps such as geology, geomorphology, soil hydrological group, land use / land cover and drainage map were prepared for the study area. The Digital Elevation Model (DEM) has been generated from the 10 m interval contour lines (which is derived from SOI, Toposheet 1:25000 scale) and obtained the slope (%) of the study area. The groundwater potential zones were obtained by overlaying all the thematic maps in terms of weighted overlay methods using the spatial analysis tool in ArcGIS 9.2. During weighted overlay analysis, the ranking has been given for each individual parameter of each thematic map and weights were assigned according to the influence such as soil −25%, geomorphology − 25%, land use/land cover −25%, slope − 15%, lineament − 5% and drainage / streams − 5% and find out the potential zones in terms of good, moderate and poor zones with the area of 49.70 km², 261.61 km² and 46.04 km² respectively. The potential zone wise study area was overlaid with village boundary map and the village wise groundwater potential zones with three categories such as good, moderate and poor zones were obtained. This GIS based output result was validated by conducting field survey by randomly selecting wells in different villages using GPS instruments. The coordinates of each well location were obtained by GPS and plotted in the GIS platform and it was clearly shown that the well coordinates were exactly seated with the classified zones.     

Flood inundation modeling using MIKE FLOOD and remote sensing data

A coupled 1D-2D hydrodynamic model, MIKE FLOOD was used to simulate the flood inundation extent and flooding depth in the delta region of Mahanadi River basin in India. Initially, the 1D model MIKE 11 was calibrated using river water level and discharge data of various gauging sites for the monsoon period (June to October) of the year 2002. Subsequently, the calibrated set up was validated using both discharge and water level data for the same period of the year 2001. The performance of calibration and validation results of MIKE 11 were evaluated using different performance indices. A bathymetry of the study area with a spatial resolution of 90m was prepared from SRTM DEM and provided as an input to the 2D model, MIKE 21. MIKE 11 and MIKE 21 models were then coupled using lateral links to form the MIKE FLOOD model set up for simulating the two dimensional flood inundations in the study area. Flood inundation is simulated for the year 2001 and the maximum flood inundation extent simulated by the model was compared with the corresponding actual inundated area obtained from IRS-1D WiFS image.     

An Analysis of Texture Measures in PCA-Based Unsupervised Classification of SAR Images

In single-band single-polarized SAR images, intensity and texture are the information source available for unsupervised land cover classification. Every textural feature measure identifies texture patterns by different approaches. For efficient land cover classification, textural measures have to be chosen suitably. Therefore, in this letter, the role of various intensity and textural measures is analyzed for their discriminative ability for unsupervised SAR image classification into various land cover types like water, urban, and vegetation areas. To make the algorithm adaptable, these textural features are fused using principal component analysis (PCA), and principal components are used for classification purposes. To highlight the effectiveness of PCA, the difference between PCA- and non-PCA-based classifications is also analyzed. Analysis of the role of texture measures for unsupervised classification of real-world SAR data with application of PCA is presented in this letter. The analysis of how every individual feature measure contributes for classification process is presented, and then, textural measures for a feature set are chosen according to their role in improving classification accuracy. By analysis, it is observed that the feature set comprising mean, variance, wavelet components, semivariogram, lacunarity, and weighted rank fill ratio provides good classification accuracy of up to 90.4% than by using individual textural measures, and this increased accuracy justifies the complexity involved in the process.     

Evaluation of a probabilistic approach to simulation of alkalinity and electrical conductivity at a river bank filtration site

In river bank filtration, impurities present in the river water travel with the bank filtrate towards the pumping well. During this passage, certain types of impurities, such as turbidity, total coliform, and so forth, may get attenuated; however, it is interesting to note that some of the instant raw river water quality parameters, such as alkalinity and electrical conductivity, increase after the passage of water through the porous medium. This occurs because water, when passing through the soil pores, absorbs many of the solutes that cause an increase in alkalinity and electrical conductivity. Measurements at a river bank filtration site for a year showed that alkalinity of 116–32 mg l^?1 in river water increased to 222.4–159.9 mg l^?1 in the river bank filtered water. Likewise, the electrical conductivity increased from 280–131 μS cm^?1 to 462–409.6 μS cm^?1. This study uses a probabilistic approach for investigating the variation of alkalinity and electrical conductivity of source water that varies with the natural logarithm of the concentration of influent water. The probabilistic approach has the potential of being used in simulating the variation of alkalinity and electrical conductivity in river bank filtrate. Copyright © 2011 John Wiley & Sons, Ltd.     

Abrupt behaviours of streamflow and sediment load variations of the Yangtze River basin,China

Monthly sediment load and streamflow series spanning 1963–2004 from four hydrological stations situation in the main stem of the Yangtze River, China, are analysed using scanning t‐test and the simple two‐phase linear regression scheme. Results indicate significant changes in the sediment load and streamflow from the upper reach to the lower reach of the Yangtze River. Relatively consistent positive coherency relations can be detected between streamflow and sediment load in the upper reach and negative coherency in the middle and lower reaches. Interestingly, negative coherency is found mainly for larger time scales. Changes in sediment load are the result mainly of human influence; specifically, the construction of water reservoirs may be the major cause of negative coherency. Accentuating the human influence from the upper to the lower reach results in inconsistent correlations between sediment load and streamflow. Decreasing sediment load being observed in recent years has the potential to alter the topographical properties of the river channel and the consequent development and recession of the Yangtze Delta. Results of this study are of practical significance for river channel management and evaluation of the influence of human activities on the hydrological regimes of large rivers. Copyright © 2012 John Wiley & Sons, Ltd.     

Fluoride enrichment in aquifers of the Thar Desert: controlling factors and its geochemical modelling

The groundwater is the only source of drinking water in the Jaisalmer district of Rajasthan, India. The study area is a part of the Thar Desert. It has low and scattered population and no industries; hence, the possibility of anthropogenic input of fluoride is almost negligible. Thus, the enrichment of fluoride is only possible due to geochemical processes taking place in the groundwater of the region. A total of 100 groundwater samples, 34 samples from Jaisalmer and 66 samples from the Pokharan administrative blocks, were collected. It was observed that the concentration of fluoride ranged from 0.08 mg/l to 4.56 mg/l in the groundwater of Jaisalmer and from 0.56 mg/l to 6.60 mg/l in the samples of the Pokharan block. The alkaline condition (average pH, 7.7 ± 0.22 and 8.01 ± 0.25 in Jaisalmer and the Pokharan administrative block, respectively) in the region favours fluorite dissolution. Ion exchange, dissolution of calcite, semi‐arid climate, alkaline conditions and weathering are responsible for fluoride enrichment in the groundwater of the study area. Copyright © 2012 John Wiley & Sons, Ltd.     

The influence of dam and lakes on the Yangtze River streamflow: long‐range correlation and complexity analyses

Employing long‐range correlation, complexity features and clustering, this study investigated the influence of dam and lake‐river systems on the Yangtze River flow. The impact of the Gezhouba Dam and the lake systems on streamflow was evaluated by analysing daily streamflow records at the Cuntan, the Yichang and the Datong station. Results indicated no evident influence of the Gezhouba Dam on streamflow changes. Distinct differences in scaling behaviour, long‐range correlation and clustering of streamflow at the Datong station when compared with those at the Cuntan and Yichang stations undoubtedly showed the influence of water storage and the buffering effect of the lake systems between the Datong station and other two hydrological stations on streamflow in the lower Yangtze River basin. Decreased regularity, enhanced long‐range correlation and increased clustering of streamflow in the lower Yangtze River basin due to the effect of water storage of the lake systems were corroborated. Copyright © 2011 John Wiley & Sons, Ltd.     

Breach erosion of earthfill dams (BEED) model

A computer model has been developed for simulation of breach erosion of earthfill dams (BEED). The model incorporates the processes of surface erosion and slope sloughing to simulate breach enlargement. Depletion of reservoir water is approximated by a volume continuity equation while broad-crested weir hydraulics is utilized to describe flow over and through the breach. Due to the implicit form of these equations, an iterative solution is proposed with convergence achieved within only a few iterations. The BEED model is written in both FORTRAN 77 and BASIC computer languages. Testing of the model using historical data of the failures of Teton and Huaccoto dams showed that timing, shape, and magnitude of the predicted outflow hydrograph were adequately simulated by this model. The same is true for the dimensions of the terminal breach. A sensitivity analysis indicated that internal friction angle and the relation for surface erosion were the major factors affecting the model results.