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Integration of optical and acoustic remote sensing data over the backshore-foreshore-nearshore continuum, a case study in Oostende (INSHORE)

Onderzoeksproject SR/00/125 (Onderzoeksactie SR)


Personen :

  • Dr.  KNAEPS Els - Vlaamse Instelling voor Technologisch Onderzoek (VITO)
    Coördinator van het project
    Betoelaagde Belgische partner
    Duur: 1/1/2009-30/6/2010
  • Dhr.  DE BATIST Marc - Universiteit Gent (UGent)
    Betoelaagde Belgische partner
    Duur: 1/1/2009-30/6/2010

Beschrijving :

Objective

The INSHORE project aims at integrating optical and acoustic remote sensing data in view of studying morpho-sedimentary processes over the nearshore-shore continuum. This corresponds to an area that comprises the dry beach (backshore), the intertidal beach (foreshore), the nearshore (lower shoreface) and the first nearshore channel. This spatial continuum will be called inshore.

INSHORE is a spin-off from former projects under the BelSPO SSD/STEREO programmes and under the authority of the Flemish Government. Since 2000, experience has been gained on the morphodynamic analysis of highly qualitative terrain surveys, both for the dune-beach zone (derived from hyperspectral and LiDAR airborne data) and for the near coastal area (derived from acoustical seaborne data).

The innovative character of INSHORE is that it integrates state-of-the-art techniques of both the airborne and seaborne realm. Each of these techniques has its own specifications and processing procedures, though through the development of a common sedimentological and morphological legend key, the data will be fine-tuned to obtain spatially integrated maps. Merging of the products and fine-tuning them to a same sedimentological and morphological classification over the inshore continuum is highly unique.

The methodology will be worked out on data from the coastal area around Oostende. This small area, about 4 km², has been selected because of the major nourishment activities that recently have been executed here. In the spring of 2004, the back- and foreshore were nourished with 575.000 m³ of sea sand; at the same time, a nearshore underwater berm was created consisting partly of sea sand and partly of gravel. The major nourishments were needed to increase the safety level of the coastline. However, they altered the geomorphology and the sedimentological characteristics of the area, creating a very interesting test site for airborne and seaborne remote sensing.

In the May/June 2009, new airborne and seaborne acquisitions are planned. An airborne hyperspectral campaign will serve to acquire a new hyperspectral dataset. The LiDAR data will be acquired in the framework of the continuous monitoring programme of the Flemish Government. Seaborne acoustic acquisitions will take place at selected parts of the seabed in function of the previous results. Adequate ground-truthing will be performed to train the classifications and to validate the derived map products. For the first time, additional remote sensing information will be sought from laserscan return pulse intensity recordings, as well as from multibeam echosounder backscatter recordings.

Two integrated data layers will be produced, the first covering the project area’s geomorphology and the second covering the surficial sediment facies classes of the area. This information will allow formulating morpho-sedimentary hypotheses on the local functioning of the coastal morphological system.

This research frames in the need for detailed scientific data to support the management and monitoring practices in the Belgian coastal zone. Integration of data over the inshore continuum is important to understand coastal erosion in a larger sediment dynamic framework. Moreover, there is wide interest from the scientific community for which detailed knowledge on the morpho-sedimentary state and dynamics is important for the set-up of realistic impact scenario’s of sea-level rise or for the prediction of the occurrence of macro benthic communities.

Method

Existing technologies, i.e. airborne hyperspectral images and LiDAR data in combination with seaborne acoustic data, are used in an innovative an synergistic way in order to map and describe the continuum of the seawall down to the seabed.
If spatially integrated maps of the sedimentology and morphology of the inshore continuum are to be made, the combined use of airborne hyperspectral and LiDAR data, in combination with seaborne acoustic data, is utmost relevant and no sound alternative exists. A methodology is in place to derive sand classes from hyperspectral data. The use of LiDAR data for topographic mapping of the Belgian coast is standard. Procedures are in place to interpret side-scan sonar and multibeam data in terms of the seabed sediment nature. Merging these products and fine-tuning them to represent similar morpho-sedimentary units, and using the classification procedures to produce spatially integrated full-coverage morphological and sedimentological geographic data layers of the inshore continuum is highly unique.

Result

The INSHORE project has a large technical component and will clarify issues on data merging and integration, resulting from optical/acoustic, airborne/seaborne technologies. This know-how will be applied over the inshore continuum with the aim of studying its morpho-sedimentological state and dynamics. Its relevance will be illustrated related to coastal zone management and monitoring, including coastal erosion.

At least for the Belgian research domain, the suggested approach is highly innovative and unique because, for the first time, an integrated, full-coverage and detailed output will be provided over the inshore continuum. This will yield new insights into the:

the state and dynamics of foreshore and nearshore nourishment berms;
the near- to offshore sediment distribution tied to probable source areas;
the inshore continuum morphology with identification of morphological units;
the impact of beach nourishment works on the morphodynamics of the inshore continuum.

These items are of utmost importance in the view of sea-level rise impact scenarios in which a good estimation of the coastal sediment budget is crucial. The high quality of the data will also allow deriving more sound parameters (e.g. sediment variability, roughness, beach slope) to be used in the modelling of the beach state, sediment transport and morphodynamics. The data are highly supportive for the prediction of the occurrence of benthic habitats as these are predominantly dependent on the sedimentological characteristics.

Related to monitoring, the nowadays practice of the Flemish Authorities consists of a yearly LiDAR survey of the fore- and backshore and independently a nearshore survey of the whole coastline. The Hydrographic Service performs offshore measurements with a frequency depending on the navigational importance of the area.

From the results and the experience that will be gained throughout this project, it is expected that a monitoring scheme can be produced in which the synergy of the approaches can be maximised. As such, it might be envisaged to tune the existing monitoring activities to the time window of the LiDAR/Hyperspectral flights.

The experience will significantly strengthen the partners’ expertise for cooperation within an international context. The project brings Belgium to the forefront of integrated mapping with applications towards monitoring and management within the perspective of integrated coastal zone management.


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