Recent Trends of Arctic and Antarctic Summer Sea-Ice Cover Observed from Space-Borne Scatterometer

Long term variations in Sea ice distribution strongly influence the atmosphere and ocean in the polar regions. In the recent period significant variations in sea ice cover have been observed in both the hemispheres. In the past, studies have been carried out that report the trends either at the Arctic/Antarctic level or at sector level. However, only a few studies have concentrated on the investigation of trends at grid level using scatterometer data. The present study focuses on the investigations of the sea ice trend at 1 × 1 degree grid level over the period 2000–2007 using QuickSCAT 0.2-degree resolution Scatterometer data. It was observed that in the Arctic overall monthly trend is negative in all the sectors, with the Arctic level decline of 3.26% per year. In the Antarctic, region-wise different trends have been observed. Negative trend is observed in the Amundsen- Bellingshausen Seas and also in the Indian Ocean sector near the continental Ice shelves. It was highlighted that significant trends exists within the pockets of marginal seas.     

Relative Radiometric Normalisation - performance testing of selected techniques and impact analysis on vegetation and water bodies

In this paper, six image-based Relative Radiometric Normalization (RRN) techniques were applied to normalize the bi-temporal Landsat 5 TM data-set. RRN techniques do not require any atmospheric and ground information at the time of image acquisition. The target image for the year 2009 was normalized in such a way that it resembled the atmospheric and sensor conditions similar to those under which the reference image of the same season for the year 1990 was acquired. Among the selected methods applied, it was found that the Iteratively Reweighted Multivariate Alteration Detection (IR-MAD) method performed better, based on the error statistic. The IR-MAD technique was found to be advantageous as it identified a large set of true time-invariant pixels automatically from the change background using iterative canonical component analysis. The technique also stretches the values of Normalized Difference Vegetation Index and Normalized Difference Water Index and may help to distinguish different vegetation and water bodies better.     

Metrics for characterizing network structure and node importance in Spatial Social Networks

Social Network Analysis offers powerful tools to analyze the structure of relationships between a set of people. However, the addition of spatial information poses new challenges, as nodes are embedded simultaneously in network space and Euclidean space. While nearby nodes may not form social ties, ties may exist at a distance, a configuration ill-suited for traditional spatial metrics that assume adjacent objects are related. As such, there are relatively few metrics to describe these nuanced situations. We advance the burgeoning field of spatial social network analysis by introducing a set of new metrics. Specifically, we introduce the spatial social network schema, tuning parameter and the flattening ratio, each of which leverages the notion of ‘distance’ to augment insights obtained by relying on topology alone. These methods are used to answer the questions: What is the social and spatial structure of the network? Who are the key individuals at different spatial scales? We use two synthetic networks with properties mimicking the ones reported in the literature as validation datasets and a case study of employer–employee network. The methods characterize the employer–employee as spatially loose with predominantly local connections and identify key individuals responsible for keeping the network connected at different spatial scales.     

Study of high energy phenomena from near space using low-cost meteorological balloons

Indian Centre for Space Physics has taken a novel strategy to study low energy cosmic rays and astrophysical X-ray sources which involve very light weight payloads up to about five kilograms on board a single or multiple balloons which are used for meteorological purposes. The mission duration could be anywhere from 3-12 hours. Our strategy provides extreme flexibility in mission preparation and its operation using a very economical budget. There are several limitations but our innovative approach has been able to extract significant amount of scientific data out of these missions. So far, over one hundred missions have been completed by us to near space and a wealth of data has been collected. The payloads are recovered and are used again. Scientific data is stored on board computer and the atmospheric data or payload location is sent to ground in real time. Since each mission is different, we present here the general strategy for a typical payload and provide some results we obtained in some of these missions.     

Space time evolution of sand bed topography and associated flow turbulence: experiments with statistical analysis

A series of flume experiments were conducted with varying the flow discharges at the Fluvial Mechanics Laboratory of Indian Statistical Institute (Kolkata) to understand the co-evolution patterns of generating bed forms and the corresponding flow turbulence. Instantaneous bed elevations and velocity components were recorded continuously for sufficient time using high resolution instruments, such as, Ultrasonic Ranging System and acoustic Doppler velocimeter, at some spatial location over the deformed bed for each flow discharge. Increase in mean bed elevations and bed-slopes was found to be increased in discharge. Heavy-tailed nature of the probability density functions of magnitude of bed elevation increments, magnitude of single continuous bed elevation increments and instantaneous Reynolds shear stresses along three planes were analyzed using Pareto and truncated Pareto distributions. The spectral analysis of bed elevations revealed that the slope of log–log linearity increased with increase in flow discharge. Wavelet cross-correlations depicted strong dependence of bed form evolution on the corresponding instantaneous Reynolds shear stress along xz-plane. A Gram–Charlier type of distribution was used to estimate the probability density function of fluctuating velocity components, instantaneous Reynolds shear stresses along three planes and the joint probability density functions of the fluctuating velocity components, which showed good fit with the experimental data.     

Seismic Hazard Assessment of Dhanbad City,India, by deterministic approach

Natural Hazards - Dhanbad is the largest producer of coal in the state of Jharkhand, India, and hence, it is one of the most important cities in the country. Considering the present-day importance...     

GIS based spatial data analysis for landslide susceptibility mapping

Landslide susceptibility map delineates the potential zones for landslides occurrence. The paper presents a statistical approach through spatial data analysis in GIS for landslide susceptibility mapping in parts of Sikkim Himalaya. Six important causative factors for landslide occurrences were selected and corresponding thematic data layers were prepared in GIS. Topographic maps,satellite image,field data and published maps constitute the input data for thematic layer preparation. Numerical weights for different categories of these factors were determined based on a statistical approach and the weighted thematic layers were integrated in GIS environment to generate the landslide susceptibility map of the area. The landslide susceptibility map classifies the area into five different landslide susceptible zones i.e.,very high,high,moderate,low and very low. This map was validated using the existing landslide distribution in the area.     

Modulation of ionospheric conductivities during high-power wave propagation

Enhancement of conductivity tensor modification within the ionospheric plasma by electron density modulation through the temperature dependence of the recombination rates of different ionspecies caused due to electron temperature modulation during high-power wave propagation is studied. Variation of Hall and Pedersen conductivities of the ionosphere has been investigated in the height range between 85 km to 250 km. The generation of waves at the modulation frequency and its harmonics in the ELF, VLF bands in the process is discussed.     

Coordinated motion planning and control of autonomous underwatervehicle-manipulator systems subject to drag optimization

A new motion coordination algorithm for an autonomous underwater vehicle-manipulator system (UVMS) is proposed. This algorithm generates the desired trajectories for both the vehicle and the manipulator in such a way that the total hydrodynamic drag on the system is minimized. Resolution of kinematic redundancy of the system is performed at the acceleration level so that this algorithm can be incorporated into the system dynamics. The dynamics of the UVMS are modeled using a quasi-Lagrange approach. A state-space formulation of the system along with a model-based controller design for trajectory-following tasks that includes thruster dynamics is also presented. The computer simulation results demonstrate the effectiveness of this proposed method in reducing the drag on the system     

Spatial structure of hydrography and flow in a Chilean fjord,Estuario Reloncaví

Underway current velocity profiles were combined with temperature and salinity profiles at fixed stations to describe tidal and subtidal flow patterns in the middle of the northernmost Chilean fjord, Estuario Reloncaví. This is the first study involving current velocity measurements in this fjord. Reloncaví fjord is 55 km long, 2 km wide, and on average is 170 m deep. Measurements concentrated around a marked bend of the coastline, where an 8-km along-fjord transect was sampled during a semidiurnal tidal cycle in March 2002 and a 2-km cross-fjord transect was occupied, also during a semidiurnal cycle, in May 2004. The fjord hydrography showed a relatively thin (<5 m deep), continuously stratified, buoyant layer with stratification values >4 kg m⁻³ per meter of depth. Below this thin layer, the water was relatively homogeneous. Semidiurnal tidal currents had low amplitudes (<10 cm s⁻¹) that allowed the persistence of a surface front throughout the tidal cycle. The front oscillated with a period of ca. 2.5 h and showed excursions of 2 km. The front oscillations could have been produced by a lateral seiche that corresponds to the natural period of oscillation across the fjord. This front could have also caused large (2 h) phase lags in the semidiurnal tidal currents, from one end of the transect to the other, within the buoyant layer. Tidal phases were relatively uniform underneath this buoyant layer. Subtidal flows showed a 3-layer pattern consisting of a surface layer (8 m thick, of 5 cm s⁻¹ surface outflow), an intermediate layer (70 m thick, of 3 cm s⁻¹ net inflow), and a bottom layer (below 80 m depth, of 3 cm s⁻¹ net outflow). The surface outflow and, to a certain extent, the inflow layer were related to the buoyant water interacting with the ambient oceanic water. The inflowing layer and the bottom outflow were attributed to nonlinear effects associated with a tidal wave that reflects at the fjord's head. The weak subtidal currents followed the morphology of the bend and caused downwelling on the inside and upwelling on the outside part of the bend.