IMIS

Turbidity profiles were obtained using conductivity-temperature-depth (CTD) and turbidity casts from aboard a ship at 16 fixed locations spread over the Belgian part of the Scheldt estuary during monthly or bi-weekly campaigns. Th e campaigns were conducted independently of the tidal phase and spring neap tide. Turbidity was measured at various depths using an Optical Backscatter point Sensor (OBS) of RBR type XR420 CTD+. During each campaign, the sensor was calibrated using a Formazine solution standard. The water body was vertically profiled using a minimal sampling frequency of 0.1 1/s. Simultaneously, two water samples were collected at each location using a Niskin bottle at approximately half the water depth and the water surface. SPM concentrations were gravimetrically determined after filtration in the laboratory. During each campaign, 16x2 SPM water samples were collected, resulting in 32 SPM estimates. To translate turbidity to SPM, we used these 32 samples to apply a linear data fit. We assumed that the relation between turbidity and SPM is location (and time) independent, i.e., equal for every location within one campaign. Calibration of turbidity to SPM resulted in a depth-profile of SPM at 16 fixed locations in the Flemish part of the Scheldt estuary.