Retrieving the availability of light in the ocean utilisingspectral signatures of vibrational Raman scattering inhyper-spectral satellite measurements

Ocean Science

T.Dinter¹  V. V.Rozanov¹  J. P.Burrows¹  A.Bracher¹ 

DOI  :  10.5194/os-11-373-2015

学科分类：海洋学与技术

来源: Copernicus Publications

【 摘 要 】

The availability of light in the ocean is an important parameter for thedetermination of phytoplankton photosynthesis processes and primaryproduction from satellite data. It is also a useful parameter for otherapplications, e.g. the determination of heat fluxes. In this study, a methodwas developed utilising the vibrational Raman scattering (VRS) effect ofwater molecules to determine the number of photons available in the oceanwater, which is expressed by the depth integrated scalar irradianceE₀. Radiative transfer simulations with the SCIATRAN fullycoupled ocean–atmosphere radiative transfer model (RTM) show clearly therelationship ofE₀ with the strength of the VRS signal measuredat the top of the atmosphere (TOA).

Taking advantage of VRS structures in hyper-spectral satellite measurements,a retrieval technique to deriveE₀ in the wavelength regionfrom 390 to 444.5 nm was developed. This approach uses the weightingfunction differential optical absorption spectroscopy (WF-DOAS) technique,applied to TOA radiances, measured by the Scanning Imaging AbsorptionSpectrometer for Atmospheric Chartography (SCIAMACHY). Based on the approachof Vountas et al. (2007), where the DOAS method was used to fit modelled spectra ofVRS, the method was improved by using the weighting function of VRS (VRS-WF)in the DOAS fit. This was combined with a look-up table (LUT) technique,where the E₀ value was obtained for each VRS satellite fitdirectly. The VRS-WF and the LUT were derived from calculations with theSCIATRAN RTM (Rozanov et al., 2014). RTM simulations for differentchlorophyll a concentrations and illumination conditions clearlyshow that low fit factors of VRS retrieval results correspond to low amountsof light in the water column and vice versa.

Exemplarily, 1 month of SCIAMACHY data were processed and a global map of thedepth integrated scalar irradianceE₀ was retrieved. Spectralstructures of VRS were clearly identified in the radiance measurements ofSCIAMACHY. The fitting approach led to consistent results and the WF-DOASalgorithm results of VRS correlated clearly with the chlorophyllconcentration in case-I water. Comparisons of the diffuse attenuationcoefficient, extracted by VRS fit results, with the established GlobColourK_d(490) product show consistent results.

【 授权许可】

Unknown