In Situ Time Series Estimation of Downwelling Diffuse Attenuation Coefficient at Southern Bay of Bengal
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In Situ Time Series Estimation of Downwelling Diffuse Attenuation Coefficient at Southern Bay of Bengal P. Muhamed Ashraf & S. S. Shaju & D. Gayatri & P. Minu & B. Meenakumari
Received: 8 July 2012 / Accepted: 17 October 2012 # Indian Society of Remote Sensing 2012
Abstract The present study is aimed to determine the bio-optical characteristics of oceanic waters during South west monsoon in Bay of Bengal using hyperspectral radiometer. The variability of diffuse attenuation coefficient, Kd(1), with chlorophyll a showed a good relation at shorter wavelengths, indicating the effect of phytoplankton on Kd(1). The determination coefficient, R2 at 412, 443, 490 and 555 nm were greater than 0.931. A good linear relation between Kd(490) and Kd(1) was observed at shorter wavelengths. These relationships of Kd(1) provides a platform to study the underwater light field during Southwest monsoon in Bay of Bengal. Keywords Diffuse attenuation coefficient . Chlorophyll a . Photosynthetically active radiation . Tropical convergence zone . Bay of Bengal
P. M. Ashraf (*) : S. S. Shaju : P. Minu Central Institute of Fisheries Technology, Matsyapuri P.O, Cochin 682 029 Kerala, India e-mail: [email protected] D. Gayatri Indian National Centre for Ocean Information Services, Hyderabad, India B. Meenakumari Indian Council for Agricultural Research, New Delhi, India
Introduction During South-west monsoon, the west India coastal current merges with the eastward flowing Equatorial Counter Current and the part of this whole eastward flowing South-west Monsoon Current, flows northward into Bay of Bengal. This region experiences very turbulent environment with higher levels of waves and winds because of the Inter Tropical Convergence Zone located over the warmest surface waters that are associated with eastward oceanic currents (Philander et al. 1995; Pickard and Emery 2003; Francis and Gadgil 2010). Inside and outside of the intercontinental tropical convergence zone, the fluxes of heat, moisture, momentum and radiation through the surface of the ocean and in the atmosphere itself differ dramatically and the absorption properties of the water column have significance. One of the important water column property to study the characteristics of the water and light availability is diffuse attenuation coefficient for downwelling irradiance, Kd(1). It is a quasi apparent optical property, that is influenced by the angular distribution of light field as well as the nature and quantity of substances present in the medium, is of particular interest because it quantifies the presence of light, the nature of particles present in it and the depth of the euphotic zone. Kd is an indicator of the penetrating component of solar radiation. For most waters Kd(1) is largely determined by absorption
J Indian Soc Remote Sens
properties of water and is very well correlated with chlorophyll a concentration (Case I waters). Some researchers studied the variations in diffuse attenuation coefficient and its vertical distribution of chlorophyll
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