An attempt towards mapping of land use of Dehra Dun city using aerial photo-interpretation techniques

The Paper describes an effort made in mapping the existing Land Use in the City Centre of Dehra Dun, using Aerial Photo-interpretation techniques. An attempt is also made towards evolving a suitable land use classification for an Indian Urban situation as well as to test the land use classification scheme designed by the Town and Country Planning Organization (TCPO), Delhi. Black and white aerial photographs on a scale of 1:11,000 (approximately) taken by a wide angle lens camera were used. Field verification of random samples was carried out to check the validity of classification.     

Geomorphological study of sundarban deltaic estuary

Study of landforms in Sundarbans deltaic estuary is necessary in regular basis due to its importance and impact on ecology, climate and economy. Remote sensing has proved as an important tool to study this. Multi-temporal satellite data helps to delineate the various geomorphic classes in different time domain and also provide inputs to study the coastal erosion and accretion. Finer spatial and better temporal resolution will be an added adventure for this kind of study.     

Evidence for the black hole event horizon

The George Darwin Lecture presented at the Royal Astronomical Society, London, 13 December 2002, by Ramesh Narayan .     

Investigation of Hemispherical Variations of Soft X-Ray Solar Flares during Solar Cycles 21 to 24

Solar System Research - In the current investigation we have studied the distribution as well as the asymmetry of solar X-ray flares during the period 1976–2017 which corresponds to solar...     

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...     

Dramatic decline of Arctic sea ice linked to global warming

Natural Hazards - Arctic sea ice has declined rapidly over the past four decades at the rate of ??4.7% per decade leading to an imbalance in the oceanic heat flux. The study reported...     

wham: a WENO-based general relativistic numerical scheme – I. Hydrodynamics

Active galactic nuclei, X-ray binaries, pulsars and gamma-ray bursts are all believed to be powered by compact objects surrounded by relativistic plasma flows driving phenomena such as accretion, winds and jets. These flows are often accurately modelled by the relativistic magnetohydrodynamic (MHD) approximation. Time-dependent numerical MHD simulations have proven to be especially insightful, but one regime that remains difficult to simulate is when the energy scales (kinetic, thermal, magnetic) within the plasma become disparate. We develop a numerical scheme that significantly improves the accuracy and robustness of the solution in this regime. We use a modified form of the weighted essentially non-oscillatory (WENO) method to construct a finite-volume general relativistic hydrodynamics code called wham that converges at fifth order. We avoid (1) field-by-field decomposition by adaptively reducing down to two-point stencils near discontinuities for a more accurate treatment of shocks and (2) excessive reduction to low-order stencils, as in the standard WENO formalism, by maintaining high-order accuracy in smooth monotonic flows. Our scheme performs the proper surface integral of the fluxes, converts cell-averaged conserved quantities to point-conserved quantities before performing the reconstruction step, and correctly averages all source terms. We demonstrate that the scheme is robust in strong shocks, very accurate in smooth flows and maintains accuracy even when the energy scales in the flow are highly disparate.     

Maximum entropy image reconstruction-a practical non-information-theoretic approach

The maximum entropy method (MEM) of image reconstructtion is discussed in the context of incomplete Fourier information (as in aperture synthesis). Several current viewpoints on the conceptual foundation of the method are analysed and found to be unsatisfactory. It is concluded that the MEM is a form of model-fitting, the model being a non-linear transform of a band-limited function. A whole family of ’entropies’ can be constructed to give reconstructions which (a) are individually unique, (b) have sharpened peaks and (c) have flattened baselines. The widely discussed 1nB and - B1nB forms of the entropy are particular cases and lead to Lorentzian and Gaussian shaped peaks respectively. However, they hardly exhaust the possibilities-for example, B^1/2 is equally good. The two essential features of peak sharpening and baseline flattening are shown to depend on a parameter which can be controlled by adding a suitable constant to the zero spacing correlation ρ₀₀. This process, called FLOATing, effectively tames much of the unphysical behaviour noted in earlier studies of the MEM. A numerical scheme for obtaining the MEM reconstruction is described. This incorporates the FLOAT feature and uses the fast Fourier transform (FFT), requiring about a hundred FFTs for convergence. Using a model brightness distribution, the MEM reconstructions obtained for different entropies and different values of the resolution parameter are compared. The results substantiate the theoretically deduced properties of the MEM. To allow for noise in the data, the least-squares approach has been widely used. It is shown that this method is biased since it leads to deterministic residuals which do not have a Gaussian distribution. It is suggested that fitting the noisy data exactly has the advantage of being unbiased even though the noise appears in the final map. A comparison of the strengths and weaknesses of the MEM and CLEAN suggests that the MEM already has a useful role to play in image reconstruction.     

Benthic Disturbance and Impact Experiments in the Central Indian Ocean Basin

As a part of the Environmental Impact Assessment studies for nodule mining, a long-term program has been initiated in the Central Indian Basin. Multidisciplinary studies on geological, biological, physical, and chemical parameters were carried out in an area selected on the basis of baseline data collected in the first phase of the program. A benthic disturbance was simulated with a hydraulic device also used in the previous experiments in the Pacific Ocean. A site of 3,000 ×200 m was repeatedly disturbed by a combination of fluidizing pump and suction pump to dislodge and discharge sediment from the seafloor into the water column 5 m above the seafloor. During 9 days of operation, 26 tows were carried out for 47 h of disturbance, resuspending about 6,000 m 3 of sediment along an 88-km line. Data for postdisturbance impact assessment were collected with sediment traps, deep-towed cameras, seafloor samples, and conductivity-temperature depth sensor (CTD)-rosette observations. Seafloor data, sediment samples, and water column studies were aimed at evaluating the impact of benthic disturbance, on the basis of pre- and postdisturbance data collected during the experiment. Observations show that vertical mixing of sediment as well as its lateral movement and resedimentation because of plume migration alters various parameters and leads to changes in the environment around the area.