Remotely sensed seasonality in the spatial distribution of sea-surface suspended particulate matter in the southern North Sea

An algorithm is presented for estimating near-surface SPM concentrations in the turbid Case 2 waters of the southern North Sea. The single band algorithm, named POWERS, was derived by parameterising Gordon's approximation of the radiative transfer model with measurements of Belgian and Dutch inherent optical properties. The algorithm was used to calculate near-surface SPM concentration from 491 SeaWiFS datasets for 2001. It was shown to be a robust algorithm for estimating SPM in the southern North Sea. Regression of annual geometric mean SPM concentration derived from remote sensing (SPM_rs), against in situ (SPM_is) data from 19 Dutch monitoring stations was highly significant with an r² of 0.87. Further comparison and statistical testing against independent datasets for 2000 confirmed the consistency of this relationship. Moreover, time series of SPM_rs concentrations derived from the POWERS algorithm, were shown to follow the same temporal trends as individual SPM_is data recorded during 2001. Composites of annual, winter and summer SPM_rs for 2001 highlight the three dominant water masses in the southern North Sea, as well as their winter–fall and spring–summer variability. The results indicate that wind induced wave action and mixing cause high surface SPM signals in winter in regions where the water column becomes well mixed, whereas in summer stratification leads to a lower SPM surface signal. The presented algorithm gives accurate near-surface SPM concentrations and could easily be adapted for other water masses and seas.