Distribution of suspended particulate matter in the North Sea as inferred from NOAA/AVHRR reflection images and in situ observations
Van Raaphorst, W.; Philippart, C.J.M.; Smit, J.P.C.; Dijkstra, F.J.; Malschaert, J.H.F.P. (1996). Distribution of suspended particulate matter in the North Sea as inferred from NOAA/AVHRR reflection images and in situ observations, in: NOWESP: 2. Compilation of scientific reports. pp. 4 [1-29] In: (1996). NOWESP: 2. Compilation of scientific reports. North-West European Shelf Programme (NOWESP): Hamburg. 324 pp., more |
| Authors | | Top | - Van Raaphorst, W.
- Philippart, C.J.M., more
- Smit, J.P.C.
| - Dijkstra, F.J.
- Malschaert, J.H.F.P.
| |
| Abstract | Distributions of suspended Particulate Matter (SPM) in the surface water of the North Sea were calculated on the basis of the 1973-1993 data base of the EC MAST North West European Shelf Programme (NOWESP) and composite reflection images constructed from data that were collected by the NOAA/AVHRR satellite in 1990-1991. Three models were used for interpolating the in situ data: (1) a distance weighted interpolation algorithm in which the in situ data are taken into account only; (2) an algorithm in which the ratio between the measured SPM and the reflection is interpolated, and the distribution of SPM is calculated from the field of interpolated ratios and the synoptic reflection image; (3) a distance weighted algorithm similar to model 1, however with an additional weight factor that is based on local differences in reflection. The models were tested for periods of 1 and 3 weeks in September 1990 and January 1991, and for the merged set consisting of all in situ data measured in September and January, respectively, between 1973 and 1993.The models 2 and 3 gave largely similar results and had a performance superior to model 1, particularly because they showed more detailed structures in the spatial distributions. Validations and cross-validations showed, however, that the absolute concentrations of SPM predicted by the models were too low at high in situ concentrations and too high at low in situ concentrations.This shortcoming is due to the relatively large degree of smoothing that we applied in the models to account for the high variance of the in situ data. Semivariograms and correlograms showed that the in situ data showed substantial variability and were poorly correlated even at short distances. Only for the 20 years merged data set some correlation (< 60%) existed for stations separated less than 50 km from each other. Monthly distributions of SPM were calculated with model 3 and the 20 year data set. The distributions confirm the main patterns found previously by others, such as the turbidity plume crossing the North Sea from southeast England towards the depository in the Skagerrak. The distributions indicate that materials from this plume may deposited in the central North Sea in spring and summer and eroded again in autumn and winter. Areas with maximum SPM concentrations were identified off the Belgian coast and north of the Wadden Sea, particularly in winter, from which particles are entrained into the main current in a narrow strip along the continental coast to the German Bight. The results suggest that the two main fluxes of SPM in the North Sea, off England and along the continental coast, remain largely separated until they both end in the Skagerrak. |
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