Ghent University: Department of Geography
CREST- project: Climate resilient coast
Approximately 250.000 people live in the low-elevation coastal area polders at the Belgian coastline. The Belgian coastline is 67 km long and consists mostly of sandy beaches with sea walls in front of the cities and dunes in between. It is situated at the southern part of the North Sea between the Netherlands and France. Next to the Netherlands, Belgium is the most vulnerable country to flooding in Europe due to rising sea levels. Moreover, the Belgian coast proves to be the most built-up region of Europe. Due to sea level rise and the high economic activity in the coastal cities, the Belgian coast suffers a high economic vulnerability for coastal flooding (see Figure 1). To protect the coast the Belgian government yearly nourishes the beaches with sand.
Figure 1: Indication of areas with a high economic vulnerability on the Belgian coast
Since the yearly volumes of sand for beach nourishments is increased, it is important to estimate aeolian sand transport to assess the artificial coastal safety by beach elevation and beach nourishment. As a result of storms a clear variation in morphology can be observed. Therefore, it is crucial to detect the variation in morphology of the intertidal zone and the rest of the sandy beach in time. Digital Surface Models (DSMs) are an indispensable data source for the management of coastal safety by beach elevation and beach nourishment.
Mobile laser scanning platform
In the framework of CREST – Climate Resilient Coast, high resolution topography surveys are carried out on a regular basis throughout the year, with a focus on high energetic storm events. These morphological surveys are performed using a prototype mobile platform (a quad type Kymco UTV 450i), aiming at a measurements before and/or after major storm events with centimeter accuracy and spatial resolution. The mobile platform is equipped with a Leica HDS6100 phase based laser scanner. Position and orientation of the moving vehicle is measured with a Novatel SPAN Global Navigation Satellite System (GNSS) and INS. RTK corrections are received from a Virtual Reference System (Flepos). The setup is shown in Figure 2.
Figure 2: The mobile laser scanning platform on the intertidal zone of the Belgian Coast
Calibration and data acquisition
After connecting the devices, calibration of the configuration is indispensable before starting every survey. The purpose of calibration is to compute the angular bias between the attitude values given by the INS and the actual value of roll, pitch and heave at the optical centre of the laser scanner. This is done using the Validator in the Processing manager of QINSy.
Figure 3: Calibration of roll, pitch and heading in the Validator
The data are logged onto a portable computer, during the survey QINSy Online is used to follow the survey lines, follow up and control all the incoming signals and systems and have a real time quality control of the acquired data.
Figure 4: Replay of the data
After the survey all data is exported from the Processing Manager in ASCII format so high resolution topographic DSMs, difference maps and profiles can be extracted and volumes calculations can be performed.
11th January 2018
Author: Annelies Vandenbulcke