Lensing, reddening and extinction effects of Mg ii absorbers from z= 0.4 to 2

Using a sample of almost 7000 strong Mg  ii absorbers with   W ₀ > 1 Å  and  0.4 < z < 2.2  detected in the SDSS DR4 data set, we investigate the gravitational lensing and dust extinction effects they induce on background quasars. After carefully quantifying several selection biases, we isolate the reddening effects as a function of redshift and absorber rest equivalent width, W ₀. We find the amount of dust to increase with cosmic time as  τ( z ) ∝ (1 + z )^−1.1±0.4  , following the evolution of cosmic star density or integrated star formation rate. We measure the reddening effects over a factor of 30 in E ( B − V ) and we find that  τ∝ ( W ₀)^1.9±0.1  , providing us with an important scaling for theoretical modelling of metal absorbers. We also measure the dust-to-metal ratio and find it similar to that of the Milky Way. In contrast to previous studies, we do not detect any gravitational magnification by Mg  ii systems. We measure the upper limit  μ < 1.10  and discuss the origin of the discrepancy. Finally, we estimate the fraction of absorbers missed due to extinction effects and show that it rises from 1 to 50 per cent in the range  1 < W ₀ < 6 Å  . We parametrize this effect and provide a correction for recovering the intrinsic  ∂ N /∂ W ₀  distribution.     

Delineation of social forestry plantations under various afforestation programmes using satellite digital data

Digital analysis of IRS 1A LISS-II (23-03-1991) data was used to delineate social forestry plantations in Matar taluka of Kheda district, Gujarat. VAX 11/780 image processing system was used to categorise the various plantations using supervised maximum likelihood classification. The classified output yielded three categories of plantations viz.,Eucalyptus spp.,Acacia spp., and mixed spp. The statistics for all the categories were also generated.     

Saline degradation of Indian agricultural lands : A case study in Khambhat Taluka,Gujarat state (India), using satellite remote sensing

In certain agricultural fields of Khambhat Taluka in Gujarat State, the salinity has increased considerably rendering the land completely infertile. The occurrence of salinity in this area can be attributed partly to subsurface sea‐water ingress and partly to improper land and water management practices prior to implementation of irrigation. Landsat MSS or TM and IRS IA LISS II data was used to test the feasibility of delineating saline soils by both visual image interpretation and digital analysis. The study of saline soils using multi‐temporal Landsat images of the year 1977, 1983, and 1987, indicated an evident increase in saline areas in past few years. The Soil Brightness Index (SBI) generated from the IRS‐IA data by the application of MSS equivalent coefficients brought out different categories of soil degradation. The supervised classification scheme aided in generating various salinity levels. The analysis of the soil samples of the above area exhibited increasing values of Electrical Conductivity (ECe), and the soluble cations with increasing levels of salinity.     

Wave reflection characteristics of plane, dentated and serrated seawalls

The hydrodynamic performance of vertical and sloped plane, dentated and serrated seawalls were investigated using physical model studies. Regular and random waves of wide range of heights and periods were used. Tests were carried out for different inclinations of the seawall (i.e. θ=30, 40, 50, 60 and 90°) and for a constant water depth of 0.7 m. The wave reflection was measured to assess the dissipation character of the seawalls. It was observed that the serrated seawall was superior to the plane and dentated seawall in reducing the wave reflection. Even for the vertical case, the coefficient of reflection due to regular waves for dentated seawall ranged from 0.6–0.99 and for the vertical serrated seawall it was 0.45–0.98, whereas for the vertical plane wall, it was almost 1.0. It was found that the characteristic dimension of the seawall (i.e. L/W) and the relative water depth (i.e. d/L) were better influencing parameters compared to the conventionally used surf similarity parameter ‘ξ’ (ξ=tan θ/(H_i/L)^0.5) in predicting the reflection from the dentated and serrated seawall, where L is the local wave length, W the width of the dent along the length of the seawall slope, d the water depth at the toe and H_i is the incident wave height. A similar trend was observed for the random waves too. The reduction in the wave reflection due to random waves for the dentated seawall as compared to the plane seawall was about 18% and for the serrated seawall, it was 20%. It was observed that the reflection due to random waves was lesser for all the three different walls than the regular waves, due to the mutual interaction of random waves. Multiple regression analysis on the measured data points was carried out and predictive equations for the reflection coefficient were obtained for both regular and random waves. This study will be useful in the design of energy dissipating type vertical quay walls in ports and harbours, sloped seawalls for shore protection from erosion and sloped caisson as breakwaters. Comparison of predictive formulae with the experimental results revealed that the prediction methods were good enough for practical purposes.     

Potential of satellite data in delineation of wastelands and correlation with ground information

In the present study an attempt has been made to delineate the wastelands at microlevel in Matar taluka of Kheda district. IRS OSS II digital data of 1991 has been used for the study which was analysed on VAX 11/780 image processing system. The digital data was classified following supervised classification algorithm. The three types of wastelands namely waterlogged, pasture/grazing and salt affected lands could be identified and mapped. The area statistics for the different wasteland categories present in the taluka were generated. Chemical analysis was also carried out for soils collected from different categories of wastelands to understand the exact nature of soils of each category.