Retrieval of sea surface velocities using sequential Ocean Colour Monitor (OCM) data

he Indian remote sensing satellite, IRS-P4 (Oceansat-I) launched on May 26th, 1999 carried two sensors on board, i.e., the Ocean Colour Monitor (OCM) and the Multi-frequency Scanning Microwave Radiometer (MSMR) dedicated for oceanographic research. Sequential data of IRS-P4 OCM has been analysed over parts of both east and west coast of India and a methodology to retrieve sea surface current velocities has been applied. The method is based on matching suspended sediment dispersion patterns, in sequential two time lapsed images. The pattern matching is performed on a pair of atmospherically corrected and geo-referenced sequential images by Maximum Cross-Correlation (MCC) technique. The MCC technique involves computing matrices of cross-correlation coefficients and identifying correlation peaks. The movement of the pattern can be calculated knowing the displacement of windows required to match patterns in successive images. The technique provides actual flow during a specified period by integrating both tidal and wind influences. The current velocities retrieved were compared with synchronous data collected along the east coast during the GSI cruise ST-133 of R.V. Samudra Kaustubh in January 2000. The current data were measured using the ocean current meter supplied by the Environmental Measurement and CONtrol (EMCON), Kochi available with the Geological Survey of India, Marine Wing. This current meter can measure direction and magnitude with an accuracy of ±5‡ and 2% respectively. The measurement accuracies with coefficient of determination (R2) of 0.99, for both magnitude (cm.s-1) and direction (deg.) were achieved

Potential of satellite based sensors for studying distribution of archaeological sites along palaeo channels: Harappan sites a case study

A large number of remote sensing based studies have shown evidence of a prominent river system, which has become buried under sand cover of Thar Desert sometime during late Holocene. This major river has been identified as Sarasvati, a legendary river mentioned in ancient Indian texts. This region is rich with archaeological sites of Harappan civilization (2500–500 BC). The present study has utilised digital image processing and enhancements techniques on multisensor satellite data followed by field investigations to reconfirm known traces and detect hitherto unknown traces of palaeochannels of Sarasvati river through parts of Indus alluvial plain in Thar desert. Potentials of IRS-P4 OCM (Primarily an Ocean Color Sensor, with eight narrow spectral channels, high radiometric resolution of 12 bits and large swath of 1420 m) could be exploited for the first time to detect hitherto unknown traces of palaeochannels of Sarasvati river through sand dune topography of Thar desert in parts of Western Rajasthan in India and adjoining parts of Pakistan by applying Principal Component Analysis technique. Pattern of palaochannels indicate westward migration of the Sarasvati river in parts of Indus alluvial plain. Database of more than 1000 archaeological sites compiled from various published sources, prepared in GIS environment could be utilised to understand their relationship with identified courses of the Sarasvati palaeochannels. Through this study it was found that there is a large spread of Mature Harappan (2200–1700 BC) sites along the palaeochannel of the Sarasvati and its tributaries in north-west India, but late Harappan (1700–1500 BC) sites are limited to further west in adjoining regions of Pakistan indicating that the shift of cluster of settlements have followed the pattern of river migration towards west. Digital terrain modelling by superimposing archaeological sites on SRTM DEM along with draped satellite data (Resourcesat-1 AWiFS and IRS-1D LISS-III) has helped in identifying geomorphological guides for archaeological investigations such as presence of relict natural levees seen as raised mounds and coincidence of known archaeological sites over them. It is suggested that other relict natural levees or raised mounds adjoining the identified palaochannel courses may be taken up for further archaeological exploration

Modelling December 2004 Indian Ocean tsunami: A coastal study

December 2004 tsunami in the Indian Ocean region has been simulated using MIKE-21 HD model. The vertical displacement of the seabed is incorporated into the numerical simulation by using time-varying bathymetry data. In the open ocean, sea surface height from altimeter observation has been used to validate the model results. To the west of the rupture zone, the crest is observed to precede the trough of the tsunami waves while to the east, trough preceded the crest. The model performance along the coastal region has been validated using de-tided sea levels from tide gauge measurements at Tuticorin, Chennai, Vishakapattanam, and Paradip ports along the east coast of India. Unique coastal characteristics of the tsunami waves, wave height, and wave celerity are reasonably simulated by the numerical model. Spectral analysis of tide gauge observations and corresponding model results has been done, and the distribution of frequency peaks from the analysis of gauge observations and the model results is observed to have a reasonable comparison. Low-frequency waves, contributed from the coastally trapped edge waves, are found to dominate both the tide gauge observations and the model results. The subsequent increase in the tsunami wave height observed at Chennai, Vishakapattanam, and Paradip has been explained on the basis of coastally trapped edge waves. From the validation studies using altimeter data and tide gauge data, it is observed that the model can be used effectively to simulate the tsunami wave height in the offshore as well as in the coastal region with satisfying performance

Synergistic Application of Optical and Radar Data for Archaeological Exploration in the Talakadu Region, Karnataka

Talakadu is a well known historic place situated on bank of the river Cauvery in Mysore district of Karnataka. The place is close to concave side of a prominent meander where large amount of sand has accumulated. It is believed that after construction of a reservoir upstream, sand was exposed to wind action burying the structures of Ganga dynasty and other later kingdoms. A number of buried sites have been identified by archaeological excavations conducted so far. Presently the area forms sand dunes with thick plantation cover. Analysis of RADAR data (fine beam RADARSAT and ENVISAT ASAR) led to identifying a hitherto unknown buried channel through the Old Talakadu town adjoining the excavated archaeological sites. The study suggests that RADAR penetration through the plantation canopy seems to have occurred as observed by comparing with corresponding optical data of LISS-IV. Below the canopy, sand and shrubs on top of the channel (topographically low area) are acting as smooth surface providing dark tone on radar imagery. During field validation GPS was extensively used to navigate through the forest canopy and locate the buried channel, excavated archaeological sites as well as other anomalous patterns. Synergistic application of optical (RESOURCESAT-1 LISS-IV and CARTOSAT-1 & 2) and radar (fine beam RADARSAT and ENVISAT ASAR) data led to identifying remote sensing based guides for archaeological exploration. Integration of known archaeological sites with the identified anomalous patterns was done in GIS environment. This study adds on to the knowledge base of the site and compliments already known information and suggested new areas for further archaeological exploration

Chlorophyll concentration studies in the Thane creek, Mumbai, India, through remote sensing: comparison of ground truth and OCNI (IRS-P4) data

The chemical analysis of the marine water samples was used along with IRS-P4 (OCM) data to prepare chlorophyll concentration maps for the Thane creek, Mumbai, India. The chlorophyll a +phaeopigment ([C+P]) retrieval was done using a bio-optical algorithm, which was applied to detect the concentration from Ocean Colour Monitor data. Marine water samples were collected on March 15, 2001, March 21, 2001, March 23, 2001 and March 25, 2001 synchronised with the IRS-P4 satellite overpass. Standard methods were used to chemically analyse the samples. The Chlorophyll distribution map from OCM data was prepared using Erdas Imagine 8.4 and SeaDas 4.0. The results show that the chlorophyll values range from 3.204mg/m(3) to 35.24mg/m(3). Discrepancies between the chlorophyll values derived using existing atmospheric model (developed by Space Application Centre, Ahmedabad, India), and those obtained from the analysis of the marine samples were removed by correlating them statistically and by applying a simple correction derived from this correlation. Lower chlorophyll values found near the mouths of the creek tributaries could be attributed to higher industrial waste discharges whereas comparatively higher values of chlorophyll seen further north in the Thane creek, are due to the nutrient disposals from domestic and food industrial sources

High-resolution residual geoid and gravity anomaly data of the northern Indian Ocean - An input to geological understanding

Geoid data are more sensitive to density distributions deep within the Earth, thus the data are useful for studying the internal processes of the Earth leading to formation of geological structures. In this paper, we present much improved version of high resolution (1' x 1') geoid anomaly map of the northern Indian Ocean generated from the altimeter data obtained from Geodetic Missions of GEOSAT and ERS-1 along with ERS-2, TOPEX/POSIDEON and JASON satellites. The geoid map of the Indian Ocean is dominated by a significant.low of 106 m south of Sri Lanka, named as the Indian Ocean Geoid Low (IOGL), whose origin is not clearly known yet. The residual geoid data are retrieved from the geoid data by removing the long-wavelength core-mantle density effects using recent spherical harmonic coefficients of Earth Gravity Model 2008 (EGM2008) up to degree and order 50 from the observed geoid data. The coefficients are smoothly rolled off between degrees 30-70 in order to avoid artifacts related to the sharp truncation at degree 50. With this process we observed significant improvement in the residual geoid data when compared to the previous low-spatial resolution maps. The previous version was superposed by systematic broad regional highs and lows (like checker board) with amplitude up to +/- 12 m, though the trends of geoid in general match in both versions. These methodical artifacts in the previous version may have arisen due to the use of old Rapp's geo-potential model coefficients, as well as sharp truncation of reference model at degree and order 50. Geoid anomalies are converted to free-air gravity anomalies and validated with cross-over corrected ship-borne gravity data of the Arabian Sea and Bay of Bengal. The present satellite derived gravity data matches well with the ship-bome data with Root Mean Square Error (RMSE) of 5.1-7.8 mGal, and this is found to be within the error limits when compared with other globally available satellite data. Spectral analysis of ship-borne and satellite data suggested that the satellite gravity data have a resolution down to 16-18 km. Further, the geoid, residual geoid and gravity anomalies are integrated with seismic data along two profiles in the Bay of Bengal and Arabian Sea, and inferences have been made in terms of density distributions at different depths. The new residual geoid anomaly map shows excellent correlation with regional tectonic features such as Sunda subduction zone, volcanic traces (Chagos-Laccadive, Ninetyeast and 85 degrees E ridges) and mid-ocean ridge systems (Central Indian and Carlsberg ridges). (C) 2012 Elsevier Ltd. All rights reserved

Low-Scale Foreshore Morphodynamic Processes in the Vicinity of a Tropical Estuary at Honnavar, Central West Coast of India

Low-scale foreshore morphodynamic processes in the vicinity of the Sharavati estuary at Honnavar, central west coast of India, are discussed in this paper based on the wave refraction analyses, sediment characteristics, and foreshore morphological changes. In general, the foreshore is composed of medium- to fine-grained (1.12–2.68), well-sorted to poorly sorted sands (0.18–0.86σ). Beaches experience two periods of accretion, one during September to December (postmonsoon) and another during February to April, followed by two periods of erosion, one during second half of May to early September (monsoon) and another a minor phase of erosion from December to February. The study indicated two distinct trends of geomorphic process on either side of the river mouth. Nearshore coastal process and wind largely control shoreface modification of the beaches to the south of the river mouth, whereas islands in this region modify geomorphic processes of the beach to the north of the river mouth. Northerly drift prevailing during the postmonsoon season favors spit growth across the river mouth from south to north, whereas the southerly drift during December to February is responsible for erosion of the portion of the beach to the north of the river mouth. The growth of a spit is at the expense of the beach to the north of the river mouth. However, during the westerly wave approach (March–April), littoral cells developed in the vicinity of river mouth provided stability to the beach

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Not AvailableSorghum anthracnose, caused by Colletotrichum graminicola, is a destructive disease, and increasing dependency on chemical fungicides for its control has serious environmental concerns since sorghum is fed to cattle. Thus there is a need to develop effective bio-pesticide for biological control of C. graminicola. Since Trichoderma is a proven biocontrol agent against plant pathogens, exploring the greater diversity that exists in Trichoderma, could be of notable economic significance in terms of disease control. To harness the hidden potential of Trichoderma strains against C. graminicola, a study was undertaken with 20 Trichoderma spp. isolated from 40 rhizospheric soil samples. Dual plate antagonism assay indicated the potential of T3, T4, T6, T15, and T19 isolates of Trichoderma against C. graminicola, with T3 isolate showing maximum (76.47%) mycelial growth inhibition. Molecular characterization based on the sequence analysis of ITS-rRNA and tef-1α genes identified these isolates as Trichoderma asperellum and Trichoderma harzianum. Under the glasshouse condition, biopriming of seed with Trichoderma spp. had significantly decreased the percent disease index to 32.92% and helped improve plant growth-promoting attributes compared to untreated control. Seed biopriming with T3 isolate exhibited higher antioxidant enzyme activities in terms of superoxide dismutase (36.63%), peroxidase (43.59%), and polyphenol oxidase (40.96%) at 48 h after pathogen inoculation. In most treatments, lignifications were highest in the epidermis, endodermis protophloem, metaphloem, pericycle, and protoxylem of sorghum roots after the 15th-day pathogen inoculation, indicating the strengthening of defense mechanism. To further evaluate, a field experiment was conducted for two consecutive years (Kharif season of 2018 and 2019) to test the best five isolates (T3, T4, T6, T15, and T19) against sorghum anthracnose. Lowest percent disease index of 54.90% and 53.68% and AUDPC value of 740.87 and 751.67 was reported from T. asperellum T3 bioprimed plants in the year 2018 and 2019, respectively, at 75 days after sowing. T. asperellum T3 isolate showed a significant increase in sorghum yield up to 22.22% and 27.29% higher than untreated control during the 2018 and 2019 Kharif season, respectively. This study indicated that T. asperellum T3 could be a potential biocontrol agent for managing the anthracnose of sorghum.Not Availabl