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Volume 13 No.1 Jan. 2009


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Episodic GPS Campaigns at Lakshadweep Islands along the Chagos-Laccadive ridge to investigate the inferred continental flexure in the west of India and the non-rigidity of the oceanic part of the Indian Plate


E.C.Malaimani, N.Ravi Kumar, A.Akilan, and K.Abhilash

National Geophysical Research Institute, Uppal Road, Hyderabad – 500 606.

The Episodic GPS campaigns were initiated at Lakshadweep islands for the first time in India by National Geophysical Research Institute (NGRI) with the objectives of refining the already estimated strain accumulation in the south of Indian peninsula, reaffirming the inferred continental flexure in the south-west of India, and investigating the rigidity of larger oceanic part of the Indian plate. To start with two sites Kavaratti and the northern most island Chetlat were chosen. With the new state-of-the-art GNSS receivers, which could track 30 GPS and 11 GLONASS Satellites with 5ºelevation mask, GPS measurements were carried out simultaneously at both Kavaratti and Chetlat for two weeks during March 2007 and repeat measurements were carried out recently in these islands. Very recently the southern most island Minicoy also was included in the experiment design and simultaneous GPS measurements were carried out in both Minicoy and Kavaratti. The acquired data was processed in the latest ITRF 2005 reference Frame. The site coordinates of Kavaratti, Chetlat and Minicoy and also the baseline lengths between Hyderabad and these three sites were estimated in the Global Network Solution. These GNSS receivers, the methodology involved, the results of estimated site coordinates and the baseline lengths between Hyderabad and these islands are discussed in this paper. The estimated baseline length between Hyderabad and Kavaratti is 991, 303.3067 ± 0.0082m. The estimated baseline length between Hyderabad and Chetlat is 892, 216.5594 ± 0.0040m. The estimated baseline length between Hyderabad and Minicoy is 1171, 071.8777 ± 0.0065m. The estimated accuracy of the baseline length is in the range of 4 to 8 mm, which shows the quality of data processing.

These studies across a 1,200-km-long “strain gauge” that is optimally oriented almost parallel to the compression seen on the land would enable the understanding whether this is due to the Himalayan collision, or the extension of the Capricorn-India diffuse boundary that could have extended this far north.


Deciphering of Weak Zones Using Cross-hole Seismic Tomography
R.S.Wadhwa, M.S.Chaudhari, A.Saha, Raja Mukhopadhyay and N.Ghosh
Central Water and Power Research Station, Pune – 411 024
Email: wadhwa_rs@cwprs.gov.in

Low strain stiffness required for deciding the levels and for designing the foundations of nuclear reactors for dynamic analysis can be determined with depth by cross-hole, up-hole or down-hole seismic techniques utilizing boreholes and polarized or directional energy sources. Of these techniques because of the well defined wave paths, cross-hole technique is the most reliable to measure in situ dynamic properties. Cross-hole seismic studies conducted at a nuclear power plant helped in establishing the foundation level of nuclear reactors as well as for determining the fundamental period of the site. At the same atomic power project site, tomographic studies helped in deciphering the lateral and vertical extent of weak zones with depth.

The foundation level of nuclear reactor both from cross-hole and tomographic analysis was evaluated to be at 12 m depth from the ground surface. P-wave tomographic studies revealed that the large region between the boreholes has a compressional wave velocity over 5 km/sec which is indicative of good quality basalt, devoid of any major fracture zone or cracks. Three weak zones of limited lateral and vertical extent inferred from the P- wave velocity tomogram should be treated to avoid any adverse effect on the foundation of nuclear reactors particularly in case of earthquake. The velocity tomogram revealed that the velocity distributions in the horizontal and vertical directions are similar which indicated that stresses both in horizontal and vertical directions are of the same order. Small abnormal features observed on the tomogram should be ignored because both technique and data can not resolve the small features. These features were attributed to error in picking arrival times, less ray density both near source and receiver hole or scattering of waves from small inhomogeneities.

Annual variability of water vapor from GPS and MODIS data over the Indo-Gangetic Plains

Sanjay Kumar, A.K.Singh, Anup K.Prasad1 and R.P.Singh1
Atmospheric Research Lab., Department of Physics, Banaras Hindu University, Varanasi- 221 005
1 Department of Physics, Computational Science and Engineering, Chapman University, One University Drive, Orange, CA 92866, USA
Email: abhay_s@rediffmail.com)

The knowledge of water vapor variability is important at any location in India for weather forecast, numerical weather prediction and also in the early information about the onset of monsoon. In the absence of ground observations, the satellite remote sensing and the Global Positioning System (GPS) have emerged as an important tool in estimation of water vapor. The total column atmospheric water vapor, obtained from Global Positioning System (GPS) and Moderate Resolution Imaging Spectroradiometer (MODIS), is found to be very dynamic over the Indo-Gangetic (IG) plains. In this paper, we present our preliminary analysis of GPS along with satellite (MODIS) derived water vapor and its annual variability over the IG plains of India (Varanasi - BHU station and Kanpur – IITK station) during the period January, 2007 to December, 2007. The monthly and seasonal variations of water vapor show strong variability and its relation with the monsoon. The role of GPS and satellite derived meteorological parameters in understanding the dynamics of the monsoon and climate conditions over Indian sub-continent are discussed.

Spatio -Temporal change study on Wetlands of Krishna delta using Remote Sensing Techniques
D.Ramprasad Naik, T.Venkateswara Rao , B.S.Prakasa Rao and N.Venkateswarlu1
Department of Geo-Engineering, College of Engineering, Andhra University. Visakhapatnam – 530 003
1National Geophysical Research Institute, Uppal Road, Hyderabad – 500 606
E.mail bosukonda@gmail.com

An attempt has been made to map and record the land use / land cover changes with reference to wetland in and around the Krishna delta region over a period of 17 years (1983 – 2000) based on interpretation of digital remote sensing data. On-screen visual interpretation was carried out on IRS - 1A (LISS I) and 1C (LISS III) digital imageries for the years 1990 and 2000 respectively coupled with field observations. Comparison of the SOI toposheet (1983) and IRS imageries resulted changes due to natural and man made activities in the study area over period of 17 years. Tremendous change has been observed in mangroves, mudflats, sandy area and plantations. The area under mangroves was decreased from 22,500 ha in 1983 to 9633 ha in 2000. Mudflats were decreased from 8700 ha to 6300 ha. About 39 % increase in plantation and 43.15% increase in sandy area has been observed from 1983 to 2000. It is concluded that most of wetlands mudflats, mangroves and agriculture land were converted to aquaculture (35,000 ha) which was not existing in 1983. This change in delta lead to the deposition of sand/silt and polluted water to the lower reaches result in mangrove degradation and sand deposition. . This paper presents the role of remote sensing studies in assessing the land use changes in unapproachable wetlands in the Krishna river delta.



Comparative study of models of Earth’s magnetic field derived from Oersted, CHAMP and SAC-C Magnetic Satellite Data
Geeta Vichare and R.Rajaram

Indian Institute of Geomagnetism, Plot No-5, Sector-18, New Panvel. Navi Mumbai – 410 218
Email: geeta@iigs.iigm.res.in

The magnetic field near the earth contains contribution from three major sources, viz., main internal field that is due to electric currents in the outer core (97-99%), crustal field (1-2%), and external field (1-2%). The external field includes contribution due to ring currents, magnetotail, magnetopause currents and also subsurface currents induced by them. Over the past decade or so, there has been an attempt at “comprehensive modeling” that seamlessly integrates data collected over different epochs and different platforms to generate an integrated magnetic field model. It is found that the estimate of the contribution from ionospheric currents using satellite observations is sensitive to the Earth’s magnetic field models, and hence it is essential to compare various magnetic field models. In the present work, we compare CHAOS model, the most recent long term model of Earth’s magnetic field that uses Oersted, CHAMP and SAC-C satellite data with earlier epoch based models such as Oersted Initial Field Model, (OIFM) and CO2 models. CO2 model utilizes magnetic measurements from all three satellites as well as ground observatory data, whereas OIFM uses single satellite observations. While both CHAOS and CO2 models expand the static (core and crustal) field up to high order spherical harmonic (n = 50 and 49 respectively), OIFM has expansion only upto degree n = 13. The present study systematically separates and discusses the contribution from the various sources. The match between the internal field obtained from OIFM and CHAOS is found to be good in the longitudinal belt between 150°E and 250°E, indicating that in this longitude zone, the contribution due to the long wavelength crustal field is minimum. It is also observed that the difference between the internal field of OIFM and CHAOS is maximum along Indian and American sectors. Present work estimates the magnetic field variations due to the ring current, induced current, and magnetotail current, as well. It is found that the ring current contribution using OIFM is stronger compared to other two models. The external field due to ring current is discovered to be largest and that of due to the tail current is weakest. The effect of the tail current on the surface of the globe is found to be almost same everywhere, due to its far location. It is evident that in general, the ring current contributions are about five times stronger than that of due to the induced currents.




Climate Change, Urbanization - What citizens can do
U.S.De and V.K.Soni1

Department of Environmental Sciences, University of Pune, Pune
1India Meteorological Department, Pune
Email: udayshankarde@gmail.com & soni_vk@yahoo.com

Anthropogenic Climate Change of post industrial era is expected impact on all sectors of the society and needs strategic steps to reduce it.
Mitigation efforts include global effort leading to curtailing the emission of green house gases. Adaptation measures on the other hand complement the mitigation measures by reducing the impact of global warming. Historically, mitigation has received more media attention due to its global canvas; while the adaptation measures have remained in the back ground. In this paper, authors have presented certain simple concepts which can be undertaken at the people's level to combat the impacts of Climate Change. In the field of mitigation, people can help reduce emission by reducing their consumption and demand for energy through use of:
(i) Energy efficient gadgets.
(ii) Eco friendly transport such as cycle for short distances and bus or car pool for longer distance travel.
(iii) Local products of food and clothing, thus avoiding energy expended in transportation.
(iv) Schools can encourage travel to and from by school buses rather than by individual transport
Urbanization is linked with development and has been quite rapid in recent years. While urban areas cover only 3% of the global land, it gives shelter to nearly 26% of the global population. The phenomenal increase in the population during the last fifty years has led to rapid industrialization and high rate of urbanization which have created tremendous pressure on natural resources like land, air and water. The urban population has increased three and half times, from 62.4 million in 1951 to 217.6 million in 1991 and it again increased to 286 million in 2001. A typical case is that during last 180 years, the urban area in the city of Pune has grown from a mere 5 Sq. Km to 700 Sq. Km. from 1901 to 2001. The urban population has grown from 1.64 lakhs to 42 lakhs. Bangalore, Hyderabad and other growing towns tell the same story. Such unplanned growth leads to widespread damage to existing ecosystem, deforestation and loss of agriculture land, apart from its effect on climate and environment. Tall concrete buildings cement roads and tarmac change the albedo of the urban areas and reduce the free flow of air. 'Heat island' is an urban effect, which is felt in all major cities in India. A study for Bangalore shows significant rise in minimum temperature during recent decades. Likewise the city of Pune shows these signatures also. Urban planning and decongesting the major urban centers by diversifying industries and other activities is needed to make urban climate more agreeable and safe for human settlement. More green cover, lakes and well spread parks are needed to make growing cities a more comfortable place to live. Action is needed now before it becomes too late to repair the damage to climate and environment due to urbanization. Citizens can play a crucial role in reducing the impacts of climate change and urbanization. Some of these are projected in the paper.



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