Target-level waveform inversion: a prospective application of the convolution-type representation for the acoustic wavefield

Nowadays, full-waveform inversion, based on fitting the measured surface data with modelled data, has become the preferred approach to recover detailed physical parameters from the subsurface. However, its application is computationally expensive for large inversion domains. Furthermore, when the subsurface has a complex geological setting, the inversion process requires an appropriate pre-conditioning scheme to retrieve the medium parameters for the desired target area in a reliable manner. One way of dealing with both aspects is by waveform inversion schemes in a target-oriented fashion. Therefore, we propose a prospective application of the convolution-type representation for the acoustic wavefield in the frequency–space domain formulated as a target-oriented waveform inversion method. Our approach aims at matching the observed and modelled upgoing wavefields at a target depth level in the subsurface, where the seismic wavefields, generated by sources distributed above this level, are available. The forward modelling is performed by combining the convolution-type representation for the acoustic wavefield with solving the two-way acoustic wave-equation in the frequency–space domain for the target area. We evaluate the effectiveness of our inversion method by comparing it with the full-domain full-waveform inversion process through some numerical examples using synthetic data from a horizontal well acquisition geometry, where the sources are located at the surface and the receivers are located along a horizontal well at the target level. Our proposed inversion method requires less computational effort and, for this particular acquisition, it has proven to provide more accurate estimates of the target zone below a complex overburden compared to both full-domain full-waveform inversion process and local full-waveform inversion after applying interferometry by multidimensional deconvolution to get local-impulse responses.     

Assessment of future water provisioning and sediment load under climate and LULC change scenarios in a peninsular river basin,India

Assessment of the impact of changes in climate and land use and land cover (LULC) on ecosystem services (ES) is important for planning regional-scale strategies for sustainability and restoration of ES. The Upper Narmada River Basin (UNRB) in peninsular India has undergone rapid LULC change due to recent agricultural expansion. The impact of future climate and LULC change on ES in the UNRB is quantified and mapped using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST 3.3.0) tool. Our results show that water yield is projected to increase under climate change (about 43% for representative concentration pathway 4.5 for 2031–2040), whereas it is projected to decrease under the LULC change scenario. Sediment export is projected to increase (by 54.53%) under LULC change for 2031–2040. Under the combined effect of climate and LULC change, both water yield and sediment export are expected to increase. Climate change has a greater impact on projected water yield than LULC change, whereas LULC has greater impact on sediment export. Spatial analysis suggests a similar trend of variation in relative difference (RD) of ES in adjacent sub-basins. The quantified changes in ES provisioning will benefit future land management, particularly for operation of the Rani Avanti Bai Sagar Reservoir downstream of the UNRB.     

Thermal evolution of the early Moon

The early thermal evolution of Moon has been numerically simulated to understand the magnitude of the impact-induced heating and the initially stored thermal energy of the accreting moonlets. The main objective of the present study was to understand the nature of processes leading to core–mantle differentiation and the production and cooling of the initial convective magma ocean. The accretion of Moon was commenced over a time scale of 100 yr after the giant impact event around 30–100 million years in the early solar system. We studied the dependence of the planetary processes on the impact scenarios, the initial average temperature of the accreting moonlets, and the size of the protomoon that accreted rapidly beyond the Roche limit within the initial 1 yr after the giant impact. The simulations indicate that the accreting moonlets should have a minimum initial averaged temperature around 1600 K. The impacts would provide additional thermal energy. The initial thermal state of the moonlets depends upon the environment prevailing within the Roche limit that experienced episodes of extensive vaporization and recondensation of silicates. The initial convective magma ocean of depth more than 1000 km is produced in the majority of simulations along with the global core–mantle differentiation in case the melt percolation of the molten metal through porous flow from bulk silicates was not the major mode of core–mantle differentiation. The possibility of shallow magma oceans cannot be ruled out in the presence of the porous flow. Our simulations indicate the core–mantle differentiation within the initial 10² to 10³ yr of the Moon accretion. The majority of the convective magma ocean cooled down for crystallization within the initial 10³ to 10⁴ yr.     

UV and X-ray Variability of Blazars

It is well established that the blazars show flux variations in the complete electromagnetic (EM) spectrum on all possible time scales ranging from a few tens of minutes to several years. Here we report the review of various UV and X-ray flux variability properties of blazars. Our analysis show that UV variability amplitude is smaller than X-rays, mostly soft X-rays hardness ratio show correlations with blazar luminosity and different modes of variability might be operating for different time scales and epochs. Quasi periodic oscillations are seen on a few occasions in blazars, higher fraction of high energy peaked blazars show intra day and short term variabilities in X-rays but variability duty cycle is much less in optical bands on intra day time scale compared to low energy peaked blazars. But these results are yet to be established.     

Seismic wave velocities of rare gas solids through elastic properties in Earth’s lower mantle

The expressions for second (SOE) and third order elastic (TOE) constants for rare gas solids are derived for comparative study of elastic behavior within the framework of many body potentials including the effect of pressure. The derived expressions are used to obtain the relations for pressure derivatives of bulk and shear moduli of RGS solids. The values of SOE, TOE constants and pressure derivative of bulk and shear modulus for Ne up to 100 GPa, Ar up to 75 GPa, for Kr up to 136 GPa and Xe up to 53.4 GPa...     

Evaluation of machine learning tools as a statistical downscaling tool: temperatures projections for multi-stations for Thames River Basin, Canada

Many impact studies require climate change information at a finer resolution than that provided by global climate models (GCMs). This paper investigates the performances of existing state-of-the-art rule induction and tree algorithms, namely single conjunctive rule learner, decision table, M5 model tree, and REPTree, and explores the impact of climate change on maximum and minimum temperatures (i.e., predictands) of 14 meteorological stations in the Upper Thames River Basin, Ontario, Canada. The data used for evaluation were large-scale predictor variables, extracted from National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis dataset and the simulations from third generation Canadian coupled global climate model. Data for four grid points covering the study region were used for developing the downscaling model. M5 model tree algorithm was found to yield better performance among all other learning techniques explored in the present study. Hence, this technique was applied to project predictands generated from GCM using three scenarios (A1B, A2, and B1) for the periods (2046–2065 and 2081–2100). A simple multiplicative shift was used for correcting predictand values. The potential of the downscaling models in simulating predictands was evaluated, and downscaling results reveal that the proposed downscaling model can reproduce local daily predictands from large-scale weather variables. Trend of projected maximum and minimum temperatures was studied for historical as well as downscaled values using GCM and scenario uncertainty. There is likely an increasing trend for T _max and T _min for A1B, A2, and B1 scenarios while decreasing trend has been observed for B1 scenarios during 2081–2100.     

Suitability Analysis of Groundwater Quality for Domestic and Irrigation Usage in Yamuna Nagar District, India: A GIS Approach

The main source to fulfill the enormous needs of water both for domestic and agricultural purposes in the densely cultivated region of Yamuna Nagar district of Haryana (India) is the water under earth. Since enough quantity of good quality water has been readily available, the water quality concerns are often neglected. In the present study analysis of the geochemical characteristics of groundwater to assess its suitability for domestic and irrigation purposes has been done. Fifty-five samples were collected in the months of June (pre-monsoon) and October (post-monsoon) from the bore wells. These samples were analysed for various parameters and were compared with various national and international standards to determine the suitability of water for domestic and irrigation use. The thematic maps for hydrogen ion concentration (pH), total dissolved solids (TDS), total hardness (TH), electric conductivity (EC), sodium adsorption ratio (SAR), percent sodium (Na%) and residual sodium carbonate (RSC) were prepared in GIS environment. These maps were further classified as per given standards to study the spatial variations of quality parameters and their suitability for drinking and irrigation purposes. Investigations revealed that groundwater in general was hard for domestic use. However it was within the safe limits for drinking. Furthermore groundwater quality was well within the desirable to permissible limits for irrigation purpose.     

First Observations from the Multi-Application Solar Telescope (MAST) Narrow-Band Imager

The Multi-Application Solar Telescope is a 50 cm off-axis Gregorian telescope recently installed at the Udaipur Solar Observatory, India. In order to obtain near-simultaneous observations at photospheric and chromospheric heights, an imager optimized for two or more wavelengths is being integrated with the telescope. Two voltage-tuneable lithium-niobate Fabry–Perot etalons along with a set of interference blocking filters have been used for developing the imager. Both of the etalons are used in tandem for photospheric observations in Fe i 6173 Å and chromospheric observation in H\(\alpha\) 6563 Å spectral lines, whereas only one of the etalons is used for the chromospheric Ca II line at 8542 Å. The imager is also being used for spectropolarimetric observations. We discuss the characterization of the etalons at the above wavelengths, detail the integration of the imager with the telescope, and present a few sets of observations taken with the imager set-up.     

Analysis of the change in temperature trends in Subansiri River basin for RCP scenarios using CMIP5 datasets

This study focuses on changes in the maximum and minimum temperature over the Subansiri River basin for different climate change scenarios. For the study, dataset from Intergovernmental Panel on Climate Change (IPCC) fifth assessment report (AR5) (i.e., coupled model intercomparison project phase five (CMIP5) dataset with representative concentration pathway (RCP) scenarios) were utilized. Long-term (2011–2100) maximum temperature (T _max) and minimum temperature (T_min) time series were generated using the statistical downscaling technique for low emission scenario (RCP2.6), moderate emission scenario (RCP6.0), and extreme emission scenario (RCP8.5). Trends and change of magnitude in T _max, T _min, and diurnal temperature range (DTR) were analyzed for different interdecadal time scales (2011–2100, 2011–2040, 2041–2070, 2070–2100) using Mann-Kendall non-parametric test and Sen’s slope estimator, respectively. The temperature data series for the observed duration (1981–2000) has been found to show increasing trends in T _max and T _min at both annual and monthly scale. Trend analysis of downscaled temperature for the period 2011–2100 shows increase in annual maximum temperature and annual minimum temperature for all the selected RCP scenarios; however, on the monthly scale, T _max and T _min have been seen to have decreasing trends in some months.

     

Validation of a satellite-based cyclogenesis technique over the North Indian Ocean

Indian region is severely affected by the tropical cyclones (TCs) due to the long coast line of about 7500 km. Hence, whenever any low level circulation (LLC) forms over the Indian Seas, the prediction of its intensification into a TC is very essential for the management of TC disaster. Satellite Application Centre (SAC) of Indian Space Research Organization (ISRO), Ahmedabad, has developed a technique to predict TCs based on scatterometer-derived winds from the polar orbiting satellite, QuikSCAT and Oceansat-II. The India Meteorological Department (IMD) has acquired the technique and verified it for the years 2010–2013 for operational use. The model is based on the concept of analogs of the sea surface wind distribution at the stage of LLC or vortex (T1.0) as per Dvorak’s classifications, which eventually leads to cyclogenesis (T2.5). The results indicate that the developed model could predict cyclogenesis with a probability of detection of 61% and critical success index of 0.29. However, it shows high over-prediction of the model is better over the Bay of Bengal than over Arabian Sea and during post-monsoon season (September–December) than in pre-monsoon season (March–June).