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The applicability of the ASED-sensor for measuring bed level changes in intertidal areas

Mus, A. (2019) The applicability of the ASED-sensor for measuring bed level changes in intertidal areas.

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Abstract:The Acoustic Sediment Elevation Dynamics (ASED)-sensor is a stand-alone measuring device designed by NIOZ, to study bed level dynamics within intertidal areas. The ASED- sensor was used to study the morphological behaviour of intertidal flats. However, the sensor was not yet properly tested and lacked an algorithm and autonomous script for translating raw intensity data into bed level data. Therefore, the objective of this study is to assess the applicability of the ASED-sensor for measuring bed level changes in intertidal areas. It includes developing the raw data processing algorithms and their implementation in Python scripts. The ASED-sensor uses a pulsed acoustic signal of approximately 300 kHz to measure bed levels during submerged conditions. The reflected signal by the bed is detected by a sudden increase in amplitude. The travel time of the signal from the sensor to the bed and vice versa needs to be converted to a distance, to obtain bed levels. The sensor will be tested both in the lab and in the field. Lab experiments need to be collected to verify whether the ASED-sensor can detect the echo and measure the travel time in a range of environmental conditions in the water tank and wave flume at NIOZ in Yerseke. The environmental conditions consisted of water depths, soil types, dilutions of soil types, and waves and current forcing. Thereafter the ASED-sensor was deployed to measure in the field. The field experiments were performed in the Eastern Scheldt, next to NIOZ, and in the Western Scheldt at the Kapellebank. The Eastern Scheldt experiment was performed during a weekend, while the Western Scheldt experiment collected data for 19 days. The lab experiments and the Eastern Scheldt experiment were validated with a manual measurement using a tape measure. The validation of the Western Scheldt experiment’s data was accomplished by a tape measure and erosion pins. At the start of the study, the ASED-sensor lacked an autonomous script for translating raw intensity data into bed level data. Therefore, three algorithms were tested, consisting of Fast Fourier Transform, envelope method and the Kalman filter. The Kalman filter method showed the most promising results, with the lowest standard deviation and lowest computation time. Parameter settings within the script were determined using the lab and field experiments. The parameter settings are filtering noise and searching the start of the sudden increase in amplitude of the first strong signal reflected by the bed. These parameters tune the bed detection of the ASED-sensor. The practical measurement domain for the ASED-sensor is from 0.20 m to 0.45 m, according to the raw data analysis of all lab experiments. The coefficient of determination (
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/77930
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