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Velloth S.,Center for Marine Living Resources and Ecology | Mupparthy R.S.,National Center for Medium Range Weather Forecasting | Raghavan B.R.,Mangalore University | Nayak S.,Earth System Science Organisation
International Journal of Remote Sensing | Year: 2014

Among the various remote-sensing options available today to map ecomorphological classes of corals, hyperspectral remote sensing is one of the best options by virtue of its spectral capabilities, while high spatial resolution is a necessary condition to resolve finer morphological features spatially. Given high-spatial resolution data of equal to or better than 30 m, the discrimination capability of end-members of multi-/hyperspectral satellite data is dependent on the efficacy of the correction for atmospheric effects and the intervening water column. In this study, a coupled approach to account for oceanic and atmospheric radiative contributions, called the Coupled Ocean Atmosphere Radiative Transfer (COART), was applied to Earth Observing 1 (EO-1) mission Hyperion image data acquired over the coral reefs of Agatti Island in the Lakshadweep Islands, Arabian Sea and Flat Island in the Andaman Islands, Bay of Bengal, India. The paper presents an open-source approach to correct and perform unsupervised classification of Hyperion imagery using a custom-built software toolkit called HyperCorals. The study finds that Hyperion has sufficient capabilities for discrimination of a few ecomorphological classes and can be improved further by using coupled radiative transfer models. Correcting for the intervening water column helps in classifying submerged features. The k-means classification offers a simpler classification method to classify an image of a subset with 42 selected spectral channels of Hyperion in the visible and near infrared (VNIR) region than the traditional Iterative Self-Organizing Data Analysis Technique (ISODATA). The classification results using the cosine distance metric over 42 selected spectral channels of Hyperion in the VNIR region offer the potential to differentiate between various ecomorphological zones. The study also presents results from sensitivity analysis experiments and discusses the relative importance of three parameters: water column depth, bottom albedo, and chlorophyll concentration on the overall correction and classification of the imagery. © 2014 Taylor & Francis.

Nayak S.,Earth System Science Organisation | Usha T.,ICMAM Project Directorate | Kankara R.S.,ICMAM Project Directorate | Reddy N.T.,ICMAM Project Directorate
Marine Geodesy | Year: 2012

Coastal topography is the principal variable that affects the movement of the tsunami wave on land. Therefore, land surface elevation data are critical to a tsunami model for computing extent of inundation. Elevation data from India's remote sensing satellite CARTOSAT-1 are available for the entire Indian coastline, while elevation data collected using Airborne Laser Terrain Mapper (ALTM) are only available for selected sections of the coastline. This study was carried out to evaluate the suitability of CARTOSAT-1 and ALTM elevation data sets in the tsunami inundation modeling. Two areas of the coastal Tamil Nadu that were severely affected during the December 2004 tsunami and surveyed extensively for mapping the extent of inundation were selected as the study areas. Elevation data sets from ALTM, CARTOSAT-1 and field measurement collected using Real-time Kinematic GPS (RTK-GPS) were compared for these areas. The accuracy of ALTM and CARTOSAT-1 data, the significance of interpolation methods and data used on model outputs were studied. The analysis clearly revealed that the elevation accuracy of CARTOSAT-1 data (+/-2m) was much lower than ALTM data (+/-0.6m). However, it was found that despite the differing elevation accuracy, both ALTM and CARTOSAT-1 can be used to produce tsunami inundation maps for open coasts with an accuracy of 185 m (2 grid cells) at 75% and 50% confidence level, respectively. © 2012 Copyright Taylor and Francis Group, LLC.

Harikumar R.,Indian National Center for Ocean Information Services | Hithin N.K.,Indian National Center for Ocean Information Services | Balakrishnan Nair T.M.,Indian National Center for Ocean Information Services | Sirisha P.,Indian National Center for Ocean Information Services | And 4 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2015

Ocean state forecast (OSF) along ship routes (OAS) is an advisory service of the Indian National Centre for Ocean Information Services (INCOIS) of the Earth System Science Organization (ESSO) that helps mariners to ensure safe navigation in the Indian Ocean in all seasons as well as in extreme conditions. As there are many users who solely depend on this service for their decision making, it is very important to ensure the reliability and accuracy of the service using the available in situ and satellite observations. This study evaluates the significant wave height (Hs) along the ship track in the Indian Ocean using the ship-mounted wave height meter (SWHM) on board the Oceanographic Research Vessel Sagar Nidhi, and the Cryosat-2 and Jason altimeters. Reliability of the SWHM is confirmed by comparing with collocated buoy and altimeter observations. The comparison along the ship routes using the SWHM shows very good agreement (correlation coefficient > 0.80) in all three oceanic regimes, [the tropical northern Indian Ocean (TNIO), the tropical southern Indian Ocean (TSIO), and extratropical southern Indian Ocean (ETSI)] with respect to the forecasts with a lead time of 48 h. However, the analysis shows ~10% overestimation of forecasted significant wave height in the low wave heights, especially in the TNIO. The forecast is found very reliable and accurate for the three regions during June-September with a higher correlation coefficient (average = 0.88) and a lower scatter index (average = 15%). During other months, overestimation (bias) of lower Hs is visible in the TNIO. © 2015 American Meteorological Society.

Harikumar R.,Indian National Center for Ocean Information Services | Balakrishnan nair T.M.,Indian National Center for Ocean Information Services | Bhat G.S.,Indian Institute of Science | Nayak S.,Earth System Science Organisation | And 2 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2013

A network of ship-mounted real-time Automatic Weather Stations integrated with Indian geosynchronous satellites [Indian National Satellites (INSATs)] 3A and 3C, named Indian National Centre for Ocean Information Services Real-Time Automatic Weather Stations (I-RAWS), is established. The purpose of I-RAWS is to measure the surface meteorological-ocean parameters and transmit the data in real time in order to validate and refine the forcing parameters (obtained from different meteorological agencies) of the Indian Ocean Forecasting System (INDOFOS). Preliminary validation and intercomparison of analyzed products obtained from the National Centre for Medium Range Weather Forecasting and the European Centre for Medium-Range Weather Forecasts using the data collected from I-RAWS were carried out. This I-RAWS was mounted on board oceanographic research vessel Sagar Nidhi during a cruise across three oceanic regimes, namely, the tropical Indian Ocean, the extratropical Indian Ocean, and the Southern Ocean. The results obtained from such a validation and intercomparison, and its implications with special reference to the usage of atmospheric model data for forcing ocean model, are discussed in detail. It is noticed that the performance of analysis products from both atmospheric models is similar and good; however, European Centre for Medium-Range Weather Forecasts air temperature over the extratropical Indian Ocean and wind speed in the Southern Ocean are marginally better. © 2013 American.

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