M.A. Eleveld

User requirements and information definition for a virtual coastal and marine data warehouse

The European Commission supports the development of a European Virtual Coastal and Marine Data Warehouse called CoastBase that aims to improve data and information search and exchange. This paper discusses a study of user requirements and defines relevant and obtainable data and information within the CoastBase project. Thematic as well as technical considerations were taken into account in the study. CoastBase aims to satisfy a variety of users. Potential users interested in data and information on various aggregation levels are represented within the CoastBase consortium. They described their requirements, initially unguided but later guided by a few broad questions about their present work and about the potential role of CoastBase in facilitating it. The results were grouped and summarised. Institutional user groups were formed based on the focus of the organisations on European, regional, national, and local issues, respectively. Individual users were grouped according to their function as Decision & policy maker, Policy advisor & project manager, Researcher, or Database administrator & programmer, respectively. The study has shown that the individual user groups in particular differed in their preferences for aggregation level of the data and information to be extracted from CoastBase. Implications, in the form of envisioned dissimilar use of the CoastBase system are discussed. Both institutional and individual users had different preferences for topic and geographical area to be covered in the CoastBase prototype. However, the study provided a useful synthesis for discussion in plenary, and led to identification of two thematic scenarios for development of the prototype, which are Eutrophication in the North Sea, and Planning in the North Sea and Mediterranean coastal zone. In addition, a comprehensive list of requirements and recommendations for the technical development and evaluation of the system had been compiled from the user requirements. This list, which was approved by the consortium, is included in the paper.

Divergent options to cope with vulnerability in subsiding deltas

Net subsidence of most major deltas in the world and related vulnerability are thought to be increasing, and this is often linked causally to human activities. This paper examines this causality against a range of co-varying factors. We do so with a principal component analysis of co-variability of a range of geophysical and socio-economical indicators of 33 deltas mainly derived from the DIVA tool. Land potentially lost and people at risk of flooding are our indicators of vulnerability. The former correlated positively with maximum surge height and negatively with net sea level rise. The latter correlated positively with delta area, average river discharge, and maximum surge and negatively with net uplift (or subsidence). Thus, variation in societal vulnerability across deltas depends on short-term, instantaneous risks linked to lowland area, river discharge and storm surges rather than on longer-term, slow, net sea level rise. Delta management should focus on precautionary spatial planning, and on maintenance or restoration of historical sediment delivery and accretion rates. Especially larger deltas with high population densities combine a high risk with the potential to accommodate flood water and mitigate flooding risks. The deltas of the Yangtze-Kiang and Ganges-Brahmaputra share these characteristics. Here space should allow engineering of flood retention, sedimentation and diversion channels as well as refuges and safe economic hotspots. At the other end, in deltas with a high population density and limited space, like the Chao Praya, means for adaptation must be sought outside the delta proper. In deltas with low population densities, such as the Lena, Yukon or Fly, natural delta dynamics can prevail.

An Optical Classification Tool for Global Lake Waters

Shallow and deep lakes receive and recycle organic and inorganic substances from within the confines of these lakes, their watershed and beyond. Hence, a large range in absorption and scattering and extreme differences in optical variability can be found between and within global lakes. This poses a challenge for atmospheric correction and bio-optical algorithms applied to optical remote sensing for water quality monitoring applications. To optimize these applications for the wide variety of lake optical conditions, we adapted a spectral classification scheme based on the concept of optical water types. The optical water types were defined through a cluster analysis of in situ hyperspectral remote sensing reflectance spectra collected by partners and advisors of the European Union 7th Framework Programme (FP7) Global Lakes Sentinel Services (GLaSS) project. The method has been integrated in the Envisat-BEAM software and the Sentinel Application Platform (SNAP) and generates maps of water types from image data. Two variations of water type classification are provided: one based on area-normalized spectral reflectance focusing on spectral shape (6CN, six-class normalized) and one that retains magnitude with no modification to the reflectance signal (6C). This resulted in a protocol, or processing scheme, that can also be applied or adapted for Sentinel-3 Ocean and Land Colour Imager (OLCI) datasets. We apply both treatments to MERIS imagery of a variety of European lakes to demonstrate its applicability. The studied target lakes cover a range of biophysical types, from shallow turbid to deep and clear, as well as eutrophic and dark absorbing waters, rich in colored dissolved organic matter (CDOM). In shallow, high-reflecting Dutch and Estonian lakes with high sediment load, 6C performed better, while in deep, low-reflecting clear Italian and Swedish lakes, 6CN performed better. The 6CN classification of in situ data is promising for very dark, high CDOM, absorbing lakes, but we show that our atmospheric correction of the imagery was insufficient to corroborate this. We anticipate that the application of the protocol to other lakes with unknown in-water characterization, but with comparable biophysical properties will suggest similar atmospheric correction (AC) and in-water retrieval algorithms for global lakes.

Chi-square spectral fitting for concentration retrieval, automatic local calibration, quality control, and water type detection

In this study, the inverse bio-optical model HYDROPT was calibrated with regional specific inherent optical properties (SIOPs) and various local SIOPs to examine the effect of these calibrations on the retrievals. The study area, the Wadden Sea, is an estuary and tidal flat area with very high concentrations of chlorophyll a (Chl a), suspended particulate matter (SPM), and coloured dissolved organic matter (CDOM). HYDROPT could derive concentrations of Chl a, SPM, and CDOM with a reasonable degree of accuracy when in situ above-water reflectances were used as input (root mean squared error of 0.19–0.52 mg·m−3 for Chl a, 0.28–0.46 mg·m−3 for SPM, and 0.20–0.34 m−1 for aCDOM). However, quality control showed that 70% of the in situ input reflectance spectra were ambiguous; these spectra could be modelled with various sets of SIOPs. Therefore, automatic local calibration based on the spectral fit (χ2) value of the fitting procedure did not necessarily lead to the best results; this was expected to be an advantage of χ2 fitting. When MERIS data were used as input, the concentration maps showed distributions according to the expectations, although tidal flats and nearby land affected the results at the locations that matched with in situ stations. The water types (water with similar SIOPs) that could be detected based on MERIS data were new in this study.

DESIMA: A Decision Support Tool for Integrated Coastal Zone Management

Evaluating engineering solutions to coastal erosion and assessing the potential impacts of oil spills are some of the tasks that management authorities in Europe’s coastal regions are concerned with. The Inland and Marine Waters Unit of the European Commission’s Joint Research Centre aims to support these authorities through the development of methods, tools and systems that integrate distributed coastal data and information. This chapter introduces a distributed information system, called DESIMA, that has been specifically created to support (European) integrated coastal zone management. The DESIMA-Demonstrator was designed to show the possibilities of such a distributed system. A key requirement for its design and implementation was that large data sets remain with data providers and that their data formats did not have to be changed. Furthermore, users had to have realtime access to data and models through a system architecture and user interface that allow interpretation of various formats on a single PC or workstation using a regular browser. To meet these requirements, the Common Object Request Broker Architecture (CORBA) was selected as a basis for the design of the DESIMA-Demonstrator, whereas Java was used for the user interface. Two applications, a coastal protection scenario and an oil spill scenario, demonstrate how a user can benefit from the DESIMA concept by using data and software that are implemented and maintained elsewhere. The coastal protection scenario enables the appraisal of three coastal management options in relation to flood risk for the town of West Bay (UK). The oil spill scenario simulates the evolution of an oil slick in the Gulf of Lion (France) and provides land cover data that allows the user to assess possible onshore impacts.

Validation of a spectral correction procedure for sun and sky reflections in above-water reflectance measurements

A three-component reflectance model (3C) is applied to above-water radiometric measurements to derive remote-sensing reflectance Rrs (λ). 3C provides a spectrally resolved offset Δ(λ) to correct for residual sun and sky radiance (Rayleigh- and aerosol-scattered) reflections on the water surface that were not represented by sky radiance measurements. 3C is validated with a data set of matching above- and below-water radiometric measurements collected in the Baltic Sea, and compared against a scalar offset correction Δ. Correction with Δ(λ) instead of Δ consistently reduced the (mean normalized root-mean-square) deviation between Rrs (λ) and reference reflectances to comparable levels for clear (Δ: 14.3 ± 2.5 %, Δ(λ): 8.2 ± 1.7 %), partly clouded (Δ: 15.4 ± 2.1 %, Δ(λ): 6.5 ± 1.4 %), and completely overcast (Δ: 10.8 ± 1.7 %, Δ(λ): 6.3 ± 1.8 %) sky conditions. The improvement was most pronounced under inhomogeneous sky conditions when measurements of sky radiance tend to be less representative of surface-reflected radiance. Accounting for both sun glint and sky reflections also relaxes constraints on measurement geometry, which was demonstrated based on a semi-continuous daytime data set recorded in a eutrophic freshwater lake in the Netherlands. Rrs (λ) that were derived throughout the day varied spectrally by less than 2 % relative standard deviation. Implications on measurement protocols are discussed. An open source software library for processing reflectance measurements was developed and is made publicly available.

Variability of adjacency effects in sky reflectance measurements

Sky reflectance Rsky(λ) is used to correct in situ reflectance measurements in the remote detection of water color. We analyzed the directional and spectral variability in Rsky(λ) due to adjacency effects against an atmospheric radiance model. The analysis is based on one year of semi-continuous Rsky(λ) observations that were recorded in two azimuth directions. Adjacency effects contributed to Rsky(λ) dependence on season and viewing angle and predominantly in the near-infrared (NIR). For our test area, adjacency effects spectrally resembled a generic vegetation spectrum. The adjacency effect was weakly dependent on the magnitude of Rayleigh- and aerosol-scattered radiance. The reflectance differed between viewing directions 5.4±6.3% for adjacency effects and 21.0±19.8% for Rayleigh- and aerosol-scattered Rsky(λ) in the NIR. Under which conditions in situ water reflectance observations require dedicated correction for adjacency effects is discussed. We provide an open source implementation of our method to aid identification of such conditions.