Remote sensing retrieval of total absorption coefficient in the Bohai Sea

Abstract

Temporal and spatial patterns of inherent optical properties in the Bohai Sea are very complex. In this paper, we used 77 groups of field data of AOPs (apparent optical properties) and IOPs (inherent optical properties) collected in June, August, and September of 2005 in the Bohai Sea, to retrieve the spectral total absorption coefficient a(λ) with the quasi-analytical algorithm (QAA). For QAA implementation, different bands in the region 680–730 nm (in 5 nm intervals) were selected and compared, to determine the optimal band domain of the reference wavelength. On this basis, we proposed a new algorithm (QAA-Com), a combination of QAA-685 and QAA-715, according to turbidity characterized by a(440). The percentage difference of model retrievals in the visible domain was between 4.5%–45.1%, in average of 18.8% for a(λ). The QAA model was then applied to Medium Resolution Imaging Spectrometer (MERIS) radiometric products, which were temporally and spatially matched with in-situ optical measurements. Differences between MERIS retrievals and in-situ values were in the range 9.2%–27.8% for a(λ) in the visible domain. Major errors in satellite retrieval are attributable to uncertainties of QAA model parameters and in-situ measurements, as well as imperfect atmospheric correction of MERIS data by the European Space Agency (ESA). During a storm surge in April 2009, time series of MERIS images together with the QAA model were used to analyze spatial and temporal variability of the total absorption coefficient pattern in the Bohai Sea. It is necessary to collect more independent field data to improve this algorithm.