TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 64 (No. 4), pp. 561-566, 2008

Short Contribution

Estimation of the in situ Ultraviolet-A Absorption of Seawater by a Simple Irradiance Inversion Model

Takafumi Hirata*

Centre for observation of Air-Sea Interactions and fluXes (CASIX), Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, Devon, PL1 3DH, U.K.

(Received 25 August 2007; in revised form 4 January 2008; accepted 4 March 2008)

Abstract: An irradiance inversion model to estimate the in situ absorption coefficient of seawater has been developed for the Ultraviolet-A (UVA) wavelength domain. Input parameters are sun angle and the up- and downward planar irradiances measured for at least two depths. The present method does not require seawater to be sampled, and is a discrete wavelength method which returns the absorption coefficient at a given wavelength from the irradiances measured at that wavelength without assuming a spectral shape of any optical properties a priori. Comparison between the model results and spectrophotometric measurements shows that the model is practically useful when cloud cover in the atmosphere is ≤50%. According to the present method, measurements of the irradiances enable simultaneous observation of the in situ underwater UVA radiation level and the absorption capacity of bulk seawater using a radiometer.

*Corresponding author E-mail: tahi@pml.ac.uk

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