Marine and Earth science Group

Ahmadābād, India

Marine and Earth science Group

Ahmadābād, India
Time filter
Source Type

Nagamani P.V.,Atmospheric science and Oceanogrpahy Group | Chauhan P.,Marine and Earth science Group | Sanwlani N.,Marine and Earth science Group
Journal of the Indian Society of Remote Sensing | Year: 2011

The two main inherent optical properties (IOPs) namely absorption and back scattering coefficients were estimated using a quasi analytical algorithm (QAA) for open and coastal ocean waters of Arabian Sea. Absorption due to gelbstoff and back scattering due to the particulate matter were calculated using the quasi analytical algorithm for all the in-situ measured reflectance spectra collected in the Arabian Sea. A comparative study was made to study the spectral variability of reflectance spectra in open as well as coastal waters of Arabian Sea. Spectral analysis was made for the absorption and back scattering coefficients calculated using the QAA for both open and coastal waters. The absorption coefficient in the open ocean waters vary from a minimum value of 0.029 to a maximum value of 0.445 and it varies from a minimum value of 0.081 to a maximum value of 4.000 for the coastal waters of Arabian Sea. Absorption due to gelbstoff or the CDOM ag(λ), calculated for the Arabian Sea waters show a variation of 0.000202 to 0.112437 for open ocean waters and it varies from 0.002848 to 2.8936 for coastal waters of Arabian Sea. Particulate back scattering coefficient for open ocean waters vary from 0.0000307 to 0.006575 whereas bbp(λ) vary from 0.000167 to 0.026014 for coastal ocean waters. The minimum slope for the open ocean waters is 0.989 and maximum value of 2.147 (average value of 1.7) was observed; whereas a minimum value of 0.046 and a maximum value of 1.201 (average value of 0.6) were observed from the in-situ spectra for coastal waters of Veraval. The slope 'Y' estimated from the model is 1.957 for open ocean waters and 0.515 for coastal waters collected in the Arabian Sea. © 2011 Indian Society of Remote Sensing.

Nageswara Rao K.,Andhra University | Subraelu P.,Andhra University | Naga Kumar K.C.V.,Andhra University | Demudu G.,Andhra University | And 3 more authors.
Earth Surface Processes and Landforms | Year: 2010

River deltas are the major repositories of terrestrial sediment flux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea-level rise ultimately affecting the delta environment. Analysis of multi-date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km2 area along the entire 336-km-long twin delta coast during the past 43 years (1965-2008) with a progressively increasing rate from 1·39 km2 yr-1 between 1965 and 1990, to 2·32 km2 yr-1 during 1990-2000 and more or less sustained at 2·25 km2 yr-1 during 2000-2008. At present the Krishna has almost become a closed basin with decreased water discharges into the delta from 61·88 km3 during 1951-1959 to 11·82 km3 by 2000-2008; and the suspended sediment loads from 9 million tons during 1966-1969 to as low as 0·4 million tons by 2000-2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three-fold reduction in its suspended sediment loads from 150·2 million tons during 1970-1979 to 57·2 million tons by 2000-2006. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins. © 2010 John Wiley and Sons, Ltd.

Solanki H.U.,Marine and Earth science Group | Dwivedi R.M.,Marine and Earth science Group
Indian Journal of Geo-Marine Sciences | Year: 2015

A bio-physical model was developed to estimate zooplankton production in the Arabian Sea using satellite derived chlorophyll concentration (CC) and sea surface temperature (SST). For this, US Joint Global Ocean Flux Study (US JGOFS) 1995 cruises in-situ data has been used. A 3D plot was generated using in-situ measured chlorophyll, temperature and zooplankton bio-mass. Scatter plot indicated linear and exponential relationship between CC - zooplankton biomass, temperature and zooplankton, respectively. A typical range of 24º-26º C water temperature was found preferable for zooplankton production. Based on this study a multiple regression analysis was carried out to derive coefficients for the development of algorithm. Correlation co-efficient (r2) of multiple regression analysis was 0.78. An empirical algorithm was developed using these co-efficient. This algorithm was applied to Oceansat-1 derived chlorophyll concentration and NOAA-AVHRR derived SST to generate zooplankton images showing zooplankton biomass distribution and concentration. Model was validated through synchronous in-situ observations. Zooplankton biomass was measured on board Sagar Kanya and Sagar Sampda in the Arabian Sea. Regression analysis indicated co-relation co-efficient (r2) = 0.74. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.

Sahay A.,Marine and Earth science Group | Chauhan P.,Marine and Earth science Group | Nagamani P.V.,Marine and Earth science Group | Sanwalani N.,Marine and Earth science Group | Dwivedi R.M.,Marine and Earth science Group
Indian Journal of Marine Sciences | Year: 2011

Backscattering of coastal waters of Arabian Sea off Veraval, Gujarat, India has been reported using Quasi Analytical Algorithm (QAA) inversion method. The same is compared with the in-situ measurements. Present study compares the backscattering coefficient retrieved from QAA with the measured values of backscattering at 470 and 700 nm. Retrieved backscattering coefficient using QAA lies between 0.0005-0.0047 m -1 at 470 nm and 0.00006-0.0040 m -1 at 700 nm. This is compared with the measured backscattering coefficients. Root mean square error (RMSE) has been computed, taking logarithm (to base 10) of the measured and modeled values. RMSE for 470 nm is 0.21 and for 700 nm is 0.23. Mean percentage error has also been computed which is 19.19% at 470 nm and 43.90% at 700 nm. Field measurements show that the QAA approach overestimates the backscattering coefficient at 470 nm and 700 nm (19.19% and 43.90% respectively) in the coastal waters of Gujarat. This is possibly due to the wavelength model used in the computation of backscattering at various wavelengths.

Singh S.K.,Marine and Earth science Group | Kulkarni A.V.,Marine and Earth science Group | Chaudhary B.S.,Kurukshetra University
Journal of Earth System Science | Year: 2011

Snow is a highly reflecting object found naturally on the Earth and its albedo is highly influenced by the amount and type of contamination. In the present study, two major types of contaminants (soil and coal) have been used to understand their effects on snow reflectance in the Himalayan region. These contaminants were used in two categories quantitatively - addition in large quantity and addition in small quantity. Snow reflectance data were collected between 350 and 2500 nm spectral ranges and binned at 10 nm interval by averaging. The experiment was designed to gather the field information in controlled conditions, and radiometric observations were collected. First derivative, band absorption depth, asymmetry, percentage change in reflectance and albedo in optical region were selected to identify and discriminate the type of contamination. Band absorption depth has shown a subtle increasing pattern for soil contamination, however, it was significant for small amounts of coal contamination. The absorption peak asymmetry was not significant for soil contamination but showed a nature towards left asymmetry for coal. The width of absorption feature at 1025 nm was not significant for both the contaminations. The percentage change in reflectance was quite high for small amount of coal contamination rather than soil contamination, however, a shift of peak was observed in soil-contaminated snow which was not present in coal contamination. The albedo drops exponentially for coal contamination rather than soil contamination. © Indian Academy of Sciences.

Sarangi R.K.,Marine and Earth science Group
Marine Geodesy | Year: 2011

The daily and weekly averaged Indian Remote Sensing satellite IRS-P4 Ocean Color Monitor (OCM) derived chlorophyll images were generated and interpreted in terms of pretsunami, tsunami, and posttsunami periods in the Bay of Bengal and Andaman Sea. There has been observation of increase in chlorophyll concentration up to 5.0 mg/m3 in the tsunami-affected coastal waters. The high chlorophyll concentration lasted for about one week after the tsunami catastrophe. The standard deviation for different transects in the tsunami-affected water were plotted. The high chlorophyll has been observed for selected transects in the aftermath of the tsunami event in coastal regions, and offshore water has also shown increase in chlorophyll concentration (~1.0 mg/m3) in the Bay of Bengal. The analysis indicated that the tsunami waves might have displaced and spread the high chlorophyll coastal water towards offshore. NASA Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua daytime sea surface temperature (SST) daily images were retrieved and displayed during December 21, 2004, to January 6, 2005, and indicated the cooling (0.5-1°C) in the Bay of Bengal around Tamil Nadu and Andhra coast. The National Oceanographic and Atmospheric Prediction-National Center for Environment Prediction (NOAA-NCEP) data for five weeks (December 9, 2004-January 12, 2005) were retrieved to study the SST variability trend in prior to MODIS data and indicated 0.5-1°C cooling of the Bay of Bengal water off Kakinada, Chennai, Cuddalore, and Nagapattinam region on December 26 and 28, 2004. © Taylor & Francis Group, LLC.

Sarangi R.K.,Marine and Earth science Group
Indian Journal of Marine Sciences | Year: 2011

Impact of three different cyclones on the Bay of Bengal water and its surface chlorophyll concentration has been studied in three different zones during October-December 2000 using 24 scenes of IRS-P4 Ocean Color Monitor (OCM). The chlorophyll concentration found to be increasing up to 5.0 mg/m 3 with effect of cyclones and hurricanes. The data has been correlated with Sea Surface Temperature (SST) and wind speed from NOAA-Pathfinder-5 and Quickscat scatterometer, respectively. There has been observation of 2-3°C decrease in SST with movement of cyclone. The wind speed has peaked up to 10-15 m/sec in the cyclonic zones.

Kulkarni A.V.,Marine and Earth science Group | Rathore B.P.,Marine and Earth science Group | Singh S.K.,Marine and Earth science Group | Ajai,Marine and Earth science Group
Annals of Glaciology | Year: 2010

Indian rivers originating in the Himalaya depend on seasonal snow-cover melt during crucial summer months. The seasonal snow cover was monitored using Advanced Wide Field Sensor (AWiFS) data of the Indian Remote Sensing Satellite (IRS) and using the Normalized Difference Snow Index (NDSI) algorithm. The investigation was carried out for a period of 3 years (2004/05, 2005/06 and 2006/07) between October and June. A total of 28 sub-basins of the Ganga and Indus river basins were monitored at intervals of 5 or 10 days. Approximately 1500 AWiFS scenes were analyzed. A combination of area-altitude distribution and snow map was used to estimate the distribution of snow cover in altitude zones for the individual basins and for the western and central Himalaya. Hypsographic curve and snow-free area was used to estimate monthly snow-line elevation. The lowest snow-line altitude in the winters of 2004/05, 2005/06 and 2006/07 was observed at 2480 ma.s.l. on 25 February 2005. In Ravi basin for the year 2004/05, snow accumulation and ablation were continuous processes throughout the winter. Even in the middle of winter, the snow area was reduced from 90% to 55%. Similar trends were observed for 2005/06 and 2007/08. In Bhaga basin, snowmelt was observed in the early part of the winter, i.e. in December, and no significant melting was observed between January and April.

Srivastava P.K.,Indian Institute of Technology Kharagpur | Majumdar T.J.,Marine and Earth science Group | Bhattacharya A.K.,Indian Institute of Technology Kharagpur
Journal of Earth System Science | Year: 2010

In this study, an attempt has been made to estimate land surface temperatures (LST) and spectral emissivities over a hard rock terrain using multi-sensor satellite data. The study area, of about 6000km2, is a part of Singhbhum-Orissa craton situated in the eastern part of India. TIR data from ASTER, MODIS and Landsat ETM+ have been used in the present study. Telatemp Model AG-42D Portable Infrared Thermometer was used for ground measurements to validate the results derived from satellite (MODIS/ASTER) data. LSTs derived using Landsat ETM+ data of two different dates have been compared with the satellite data (ASTER and MODIS) of those two dates. Various techniques, viz., temperature and emissivity separation (TES) algorithm, gray body adjustment approach in TES algorithm, Split-Window algorithms and Single Channel algo- rithm along with NDVI based emissivity approach have been used. LSTs derived from bands 31 and 32 of MODIS data using Split-Window algorithms with higher viewing angle (50°) (LST1 and LST2) are found to have closer agreement with ground temperature measurements (ground LST) over waterbody, Dalma forest and Simlipal forest, than that derived from ASTER data (TES with AST 13). However, over agriculture land, there is some uncertainty and difference between the measured and the estimated LSTs for both validation dates for all the derived LSTs. LST obtained using Single Channel algorithm with NDVI based emissivity method in channel 13 of ASTER data has yielded closer agreement with ground measurements recorded over vegetation and mixed lands of low spectral contrast. LST results obtained with TIR band 6 of Landsat ETM+ using Single Channel algorithm show close agreement over Dalma forest, Simlipal forest and waterbody with LSTs obtained using MODIS and ASTER data for a different date. Comparison of LSTs shows good agreement with ground measurements in thermally homogeneous area. However, results in agriculture area with less homogeneity show difference of LST up to 2°C. The results of the present study indicate that continuous monitoring of LST and emissivity can be undertaken with the aid of multi-sensor satellite data over a thermally homogeneous region. © Indian Academy of Sciences.

Kumari B.,Marine and Earth science Group | Raman M.,Marine and Earth science Group
International Journal of Remote Sensing | Year: 2010

One of the major requirements for the growing whale shark tourism industry is to identify potential areas of their aggregation for sighting. This would require baseline information on the occurrence of whale shark and the associated environment. In this context, the relationship between whale shark landings, phytoplankton concentration and sea surface temperature (SST) in the continental shelf and offshore regions of Gujarat coast were examined using satellite data from 1998 to 2000. Monthly images of chlorophyll-a (chl-a) concentration, an index of phytoplankton biomass and SST were derived for the eastern Arabian Sea from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and National Oceanographic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR), respectively. Whale sharks (Rhincodon typus) landing data were obtained from a survey conducted by Trade Records Analysis of Flora and Fauna In Commerce (Traffic)-India of the World Wide Fund (WWF)-India and the Central Institute of Fisheries Technology (CIFT), India. Mean chl-a concentration in the study area (between 20-22° N and 69-70° E) covering the continental shelf and adjoining offshore region of coast (depth > 25 m) was observed to be significantly higher (4.23 mg m-3 in February and 3.88 mg m-3 in March) compared to regions seaward of the study area (mean of 1.51 mg m-3 for February and 1.16 mg m-3 for March) and in southern latitudes of the eastern Arabian Sea (mean of 0.27 mg m-3 for February and 0.23 mg m-3 for March). The SST in the study area ranged from 23-26°C for February and March, whereas in the southern latitudes, it ranged from 27-29°C. The SST in regions outside the study area was marginally warmer by 0.5°C. A significant relationship between whale shark landings off Gujarat, chl-a concentration and SST was observed. Results presented in this study contribute to the idea that the combined use of ocean colour and SST images are an appropriate tool to identify potential areas of whale shark aggregation for sightings. © 2010 Taylor & Francis.

Loading Marine and Earth science Group collaborators
Loading Marine and Earth science Group collaborators