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Talaulikar M.,National Institute of Oceanography of India | Thayapurath S.,National Institute of Oceanography of India | Desa E.,National Institute of Oceanography of India | Matondkar S.G.P.,National Institute of Oceanography of India | And 2 more authors.
Remote Sensing Letters | Year: 2012

The average cosine of the underwater light field μ(λ), where λ is the wavelength, is an apparent optical property (AOP) that describes the angular distribution of radiance at a given point in water. Here, we present a simple algorithm to determine the average cosine at 490 nm, μ(490), which was developed using the measured optical parameters from the eastern Arabian Sea and coastal waters off Goa. The algorithm is validated using measured optical parameters. This algorithm, based on a single optical parameter, performed better compared with other empirical algorithms in determining the average cosine of underwater light field. The absorption coefficient at 490 nm, derived as an application of μ(490), compared well with the synthetic optical data and optical data measured from other regions. © 2012 Taylor & Francis. Source


Suresh T.,National Institute of Oceanography of India | Talaulikar M.,National Institute of Oceanography of India | Desa E.,National Institute of Oceanography of India | Prabhu Matondkar S.G.,National Institute of Oceanography of India | And 2 more authors.
Marine Geodesy | Year: 2012

Marine optical parameters required for ocean color satellite applications must be measured with high accuracy and errors within the permissible limits. These stringent requirements demand careful measurements of optical parameters. Though the free-fall radiometer is found to be a better option for measuring underwater light parameters as it avoids the effects of ship shadow and is easy to operate, the measurements demand profiling the radiometer vertical in water with minimum tilt. Here we present the results of our observations on the tilts of the radiometer from the measurements in the Arabian Sea. Since there is hardly any study carried-out on the tilt of the profiling radiometer, the result of this study will help in the better design of such marine instruments. The tilt of the radiometer near the surface of the water is attributed to the mode of deployment and environment parameters, while the tilt at depth of the water is influenced by the density variations of the water. Here we also demonstrate a method of deploying the instrument that minimizes the tilt of the instrument at the surface layer of the water. © 2012 Copyright Taylor and Francis Group, LLC. Source


Silveira N.,National Institute of Oceanography of India | Suresh T.,National Institute of Oceanography of India | Talaulikar M.,National Institute of Oceanography of India | Desa E.,Indian National Center for Ocean Information and Services | And 2 more authors.
Indian Journal of Marine Sciences | Year: 2014

There are various sources of errors from the measurements of optical parameters using a radiometer, which can be classified as mode of deployment, instrument and environment. The errors from the deployment are primarily from the ship and superstructure shadows. Instrument could be a source of error arising from its self-shadow, drift in the calibration and temperature effects. There could be large errors, which at times may be unavoidable to environment factors such as wave focusing at the surface layers, sea state conditions which may affect the tilt of the instrument, atmospheric conditions such as cloud cover, solar elevation, wind and rain. Radiometric optical data in water could also get affected due to Raman scattering and fluorescence effects. Here we discuss the above sources of errors and how they could be minimized. From the measurements carried out in the coastal waters off Goa and Arabian Sea using the hypespectral radiometer, we propose simple protocol to measure the data and also screen the erroneous data measured from the radiometer. Source

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