Implementation of RISAT-1 Hybrid Polarimetric Decomposition Techniques and Analysis Using Corner Reflector Data

With recent advances in polarimetry, Synthetic Aperture Radar (SAR) with Hybrid–polarity architecture, a demonstration of compact polarimetry enabled larger swath coverage, reduced PRF and SAR system complexity as compared to fully polarimetric systems. The first Hybrid Polarimetric Space-borne SAR in Earth Observation orbit, India’s Radar Imaging Satellite (RISAT-1) is a new-fangled gateway to remote sensing user community for land and oceanic applications. In response to a right-circular polarized transmitted signal, based on the derived stokes vectors, Stokes parameters are estimated to produce several useful quantitative measures for generating polarimetric decomposed image. m-delta, m-chi and m-alpha polarimetric decomposition methods along with suitable weighting functions in terms of three principal components are implemented which maps Stokes parameters to RGB image space for representing odd bounce, even bounce and volume scattering targets. Various RISAT-1 Hybrid Fine Resolution Stripmap Single-Look Complex SAR datasets acquired over deployed corner reflectors at calibration site, Shadnagar have been considered over which different hybrid polarimetric decomposition techniques are implemented using in-house developed software. Further analysis produced encouraging results with standard point targets like dihedral and trihedral corner reflectors against distributed targets in the same scene to demonstrate the scattering mechanisms as per their characteristics when interacted with a polarized signal were presented in this paper.     

Seismic velocity imaging of the Kumaon–Garhwal Himalaya,India

Natural Hazards - Since the initial collision at 55 Ma, rocks of the Indian crust below the Himalayas have undergone modification chemically and compositionally due to the ongoing...     

Photo-electric study of the eclipsing binary RU Eridani

B andV observations of the eclipsing binary RU Eridani made on 23 nights during 1974–76 are reported. An improved period of 0^d.63219951 is derived. After rectification ofB andV light curves, new elements are derived using Russel-Merrill method. The system is classified as semidetached.     

Equations for the Estimation of Strong Ground Motions from Shallow Crustal Earthquakes Using Data from Europe and the Middle East: Horizontal Peak Ground Acceleration and Spectral Acceleration

This article presents equations for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes with magnitudes M_w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is not large and corresponds to factors between 0.8 (normal and odd) and 1.3 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.6 over those on rock sites. Disappointingly the standard deviations associated with the derived equations are not significantly lower than those found in previous studies.     

REE-HFSE distribution/partitioning between garnetiferous restites and TTG from Nademavinapura area,Western Dharwar craton

The major part of the Peninsular Gneiss in Dharwar craton is made up of Trondjhemite-Tonalite-Granodiorite (TTG) emplaced at different periods ranging from 3.60 to 2.50 Ga. The sodic-silicic magma precursors of these rocks have geochemical features characteristic of partial melting of hydrated basalt. In these TTGs, enclaves of amphibolites (± garnet) are abundant. These restites are considered to be the residue of a basaltic crust after its partial melting. A detailed study of these (residue) enclaves reveals textures formed due to the process of partial melting. Major, trace and REE analysis of these residue enclaves and the melt TTGs and microprobe analysis of the coexisting minerals show partitioning of REE and HFSE between the precursor melt of TTGs and the upper amphibolite facies residues. Formation of garnetiferous amphibolites with biotite, Cpx and plagioclase consequent to melting, has squeezed the original MORB type of basaltic crust and given rise to the TTGs, depleted in Y, Yb, K₂O, MgO, FeO, TiO₂ and enriched in La, Th, U, Zr and Hf. Coevally during the process of melting, the hydrated basalt was depleted in Na₂O, Al₂O₃, LREE, Th, U and enriched in K₂O, MgO, Nb, Ti, Yb, Y, Sc, Ni, Cr and Co. Mineral chemistry of co-existing garnet-biotite and amphibole-plagioclase in these amphibolitic (restite) enclaves indicates an average temperature of 700 ± 50° C and pressure of 5 ± 1 Kbar. These data are inferred to indicate that during the garnet stability field metamorphism, effective fractionation of HREE and HFSE has taken place between the restites having Fe-Mg silicates, ilmenites and the extracted melt generated from the MORB type of hydrated basalt. These results are strongly substantiated by the reported melting experiments on hydrated basalts.     

Impacts of SW Monsoon on Phytoplankton Community Structure Along the Western Coastal BOB: an HPLC Approach

The major Indian rivers bring significant amount of freshwater along with inorganic nutrients and sediment load in to the northern Bay of Bengal (BOB) during the southwest monsoon (SWM); the southern bay does not experience equal freshening. This contrasting pattern may considerably impact the physicochemical features and phytoplankton community composition in this bay and was investigated during a coastal cruise during the SWM covering eight river plumes from both northern and southern bay; phytoplankton pigments and physicochemical parameters were analysed from different depths (0, 10, 25, and 50 m). Significant freshening, stratification and warmer waters were noticed in the northern bay relative to its southern part. Phytoplankton pigment analysis and diagnostic pigment-based size class analysis revealed the dominance of microphytoplankton (mainly diatoms) in the northern bay and were mostly confined to the surface waters. Their abundance was positively correlated with dissolved silicate (DSi) concentrations and inversely with salinity. Nanophytoplankton and picophytoplankton (prymnesiophytes, chrysophytes and cyanophytes) were mostly noticed in the subsurface waters and dominated the southern bay. This finding suggests that the dominance of microphytoplankton in the northern bay may significantly contribute to higher particle flux which has been reported earlier. Therefore, any modification in future river discharge, which is in turn related to the intensity of Indian summer monsoon, will alter the phytoplankton community structure in the coastal BOB and may be further cascaded to the other vital ecosystem components like fisheries resources, organic carbon export flux and benthic production.     

Contrasting phytoplankton community structure and associated light absorption characteristics of the western Bay of Bengal

Absorption spectra, particulate pigments, and hydrochemical constituents were measured in the western Bay of Bengal (BoB) during July-August 2010 when influence of river discharge is at peak. Chromophoric dissolved organic matter (CDOM) absorption coefficient (a_CDOM(440)) displayed a significant inverse linear relationship with salinity in the surface waters implying conservative mixing of marine and terrestrial end members. The northern part of the study area is influenced by discharge from the river Ganga and a dominant terrestrial CDOM signal is seen. The southern part receives discharge from peninsular rivers with corresponding signals of higher CDOM than the linear model would indicate and higher UV-specific absorption coefficient (SUVA) indicating more aged and humified DOM. Lower contribution of CDOM to total non-water absorption and higher phytoplankton biomass (chlorophyll a absorption coefficient, a_ph(440)) but lower chlorophyll a specific phytoplankton absorption coefficient (a _ph ^* (440)) characterize the northern part, compared to the southern part. Chlorophyll b had a distinct linear relationship with chlorophyll a in the latter. The size index (SI) indicated dominance of microphytoplankton in the northern and nano and picophytoplankton in the southern parts. Chlorophyll a is significantly related to a _ph ^* (440) by an inverse power model in the northern part but by an inverse linear model in the southern part. Our study suggests that knowledge of the phytoplankton community structure is essential to improve chlorophyll a algorithm in the coastal Bay of Bengal.