Calibration of optical backscatter sensor for measurements of sediment transport through the Marsdiep inlet

Calibration of optical backscatter sensor for measurements of sediment transport through the Marsdiep inlet

Bertoncelj, Vesna (TU Delft Civil Engineering and Geosciences; TU Delft Environmental Fluid Mechanics)

van der Molen, Johan (mentor)
Katsman, Caroline (mentor)
de Schipper, Matthieu (graduation committee)

Delft University of Technology

2019-12-10

In highly dynamic and vulnerable tidal systems such as the Wadden Sea, the importance of understanding natural processes and how they are hampered by anthropogenic pressure is highly demanding. Within these processes the sediment transport is one of the most challenging movements to be monitored. With this in mind, suspended particulate matter (SPM) transport in the Marsdiep inlet, the southeastern most tidal inlet in the Dutch Wadden Sea, is monitored with high frequency acoustic backscattering measurements obtained with acoustic Doppler current profiler (ADCP) on Texels Eigen Stoomboot Onderneming (TESO) ferry. The calibration of ADCP measurements is practiced with another device - optical backscatter sensor (OBS). In order to obtain reliable suspended particulate matter concentration (SPMC) measurements, the first step is to calibrate OBS output with high precision. Based on the studies done in the past, the calibration needs to be done locally and regularly as the OBS is sensitive to the variability of SPM properties. The objective of the present study is to formulate an improved OBS calibration method with in situ water samples taken from the Royal Netherlands Institute for Sea Research (NIOZ) jetty. This was achieved by applying pumping suction method to collect the water samples while measuring optical backscattering signal with Campbell Scientific OBS3+ device. Subsampling of the water samples was tested and the results revealed that subsampling leads to undesirable outcome. Procedural control filters that were applied to the laboratory procedure showed filter mass loss that needs to be taken into the account, and the analysis of salt retention showed 1.06 mg of salt remaining on the filters after filtration procedure. Moreover, loss on ignition (LOI) technique revealed the amount of organic content of SPMC which is linearly correlated to full SPMC. The analysis of spring-neap tidal cycle showed that during neap tide there was 0:5 mg l^-1 more organic SPMC compared to the one during spring tide. Finally, the sources of uncertainties were identified and the guidance for further research was suggested.

Optical backscatter sensor
OBS
Marsdiep inlet
OBS calibration
Suspended Particulate Matter
SPM
Sediment transport
Wadden Sea
Loss on ignition

http://resolver.tudelft.nl/uuid:27ce0846-0a5a-49e1-b169-10352d0830c6

53.001775, 4.789047

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© 2019 Vesna Bertoncelj