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Content archived on 2023-01-04

Monitoring of the Marine Environment : Coastal Monitoring, 1992-1994

Exploitable results

Remote sensing has been applied to the study of coastal upwelling off Northwest Africa, for describing temporal both and spatial distribution. The analysis of temporal and spatial variability of coastal upwelling has been finalized. The latest development of the analysis included a quantification of the relationship between the upwelling indices derived from sea surface temperature (SST) images and meteorological data, respectively. The SST database has been updated so that more than 10 years of SST observations are available. The total number of images now exceeds 5000. Remote sensing data and a hydrodynamics model have been used in a separate study of cross shelf transport in an area off Mauritania. This particular study was carried out with the purpose of examining in detail the vertical structure and the turbulence characteristics in the upper layer of the ocean during coastal upwelling events. The model has been forced with European centre for medium range weather forecasting (ECMWF) winds, and the crosshelf distribution of temperature extracted at regular time intervals. During the same period several satellite images were available and the surface distribution of temperature was compared to the model results. The combined use of remote sensing and model contributed to the understanding of coastal upwelling as a wind driven phenomenon.
Research has been undertaken on the contribution of marine studies to the analysis of global change, in particular to assimilate data from satellite sewing and ship surveys and develop algorithms relating this data to processes occurring in the water column. Extensive data sets were collected on the vertical structure of the phytoplankton photosynthetic pigment. 1100 chlorophyll profiles were parametrized into a Gaussian distribution superimposed on a background chlorophyll concentration. Statistical analyses enabled the delineation of the studied basin into 7 biogeochemical provinces. Semianalytical algorithms were developed to comput the vertical chlorophyll profiles and total integrated pigments from satellite data. Comparison of computed and observed data showed a mean error of less than 20%. Analysis using new instrumentation has shown that phytoplankton fluorescence can be used to estimate productivity as well as the photosynthesis light parameters required for satellite models of primary production. An oceanographic survey was conducted to investigate the optical and biooptical properties of the southern Baltic. The first results illustrate the importance of yellow dissolved organic matter which efficiently competes with phytoplankton for energy. Numerical modelling was investigated. For the preparation of topographic and meteorological input data, 2 preprocessor were developed giving a specific simulation within 1 hour. In order to facilitate the access and archiving of the large data sets produced, interactive shell scripts have been developed and implemented with a data archiving system installed on a mainframe. An impaired model for the heat fluxes and the skin effect at the air sea interface has been implemented. 2 surveys have been launched on: available turbulence models; models and data for the ocean mixed layer dynamics. The hydrodynamics of up welling in typical cross sections off Africa were studied using real wind data. The different time variabilites of the turbulent mixed layer and the thermal mixed layers were demonstrated. The model adequately reproduced the temperature difference between shelf water and open ocean.
A feasibility study has been initiated to: improve access to and stimulate use of marine environment (ME) data collections and related documents; improve and simplify the maintenance of the data collections in a format and location independent manner; to evaluate the World Wide Web (WWW) as a tool to make resources and data available worldwide. The WWW suite consists of one or more central servers and several clients located at the end users machine. An experimental server has been set up and made operational within the ME unit. Together with this server, clients have been made available on all hardware platforms. 4 data collections and their documentation have been made accessible through this server client system. The requested data is sent to the user at the click of a button in a format understood by the users computer. The data can be fed into the users personal applications, examined or printed. The requested data is translated and decompressed by the client on the users machine in the format needed. Apart from having the actual data available, the documentation on the data is also accessible through the same mechanism. The core of the WWW suite is formed by one or more servers, clients, an interconnecting network and HTTP, the WWW client server protocol. Current protocols form a small subset of this protocol. HTTP is extremely lightweight and thus has very good performance over wide area networks, such as the internet. Within the ME unit several clients from different sources have been tested and installed. Currently 5 different servers are in use.
Preparation of algorithms has been undertaken to extract geophysical parameters from ocean colour data, and of methodologies for their archival, management and exploitation. Compilation of a biooptical data base on the marine environment has been initiated, using historical data, to promote the use of ocean colour data in an application demonstration programme devoted to marine regions of European interest. The definition of standard format and processing software has been completed. All software development concerning the set of the value adding algorithms, together with interfaces, formats, and suitable procedures for verification and output data validation, has been completed, and functional tests been performed. All software developed has been integrated into a single system, which will provide the backbone for the data processing systems of future ocean colour sensors. The compilation of a data archive has progressed and a data catalogue and browsing system have been made available for consultation to all interested scientific groups. The main research projects concern the assessment of pigment patterns, and their variability in both space and time; the relationships between plankton pigments and nutrients; the evaluation of plankton biomass and production; surface circulation and water constituent dispersion, including sediment transport; currents; bathymetry and islands interaction; upwelling dynamics; coastal runoff and plumes; the monitoring of potential pollution sources; and fisheries applications. The standard data selections have been obtained in the following manner: for each year and for each geographical group, a selection of all the images judges of some interest was performed, on the basis of operational criteria taking into account the image geographical coverage, seasonal period, acquisition mode and satellite altitude, acceptable cloud cover, and surface features. A final plan has been drafted for a programme on ocean colour techniques for observation, processing and utilization systems. A preliminary assessment of ocean colour applications to marine environmental issues has been undertaken and 2 workshops held on the topic. Alternative methods for the use of algorithms to determine optically active material concentrations in marine water have been investigated. Joint activities for the development of European algorithm set have also been started.
Coastal monitoring has been improved, with special reference to pollution situations, the development of methods for the analysis of remote sensing data on sea colour, and the development of bioptical algorithms relating sea colour to water composition. A radiometer is being developed for the detection of the blooms of the marine cyanobacterium tricherdesmium in oligotrophic case 1 waters. A simulation study has been carried out using a 3 component model of sea colour, explicitly accounting for the contributions of the main optical parameters (ie phytoplankton, nonchlorophyllous particles and yellow substance). The results obtained indicated that algorithms operating on the data recorded should have the capability to discriminate pixels containing trichodermium at concentrations down to 0.1 mg m{-3} chlorophyll and yield estimates of the concentration. The validity range has been explored by a sensitivity analysis. Modifications have been made to improve the procedure used for absorption measurements of aquatic particles retained on glass fibre filters. Beam transmission and beam reflection measurements were combined in order to remove the spurious contribution caused by sample back scattering, by use of a commercial integrating sphere attachment to the dual beam spectrophotometer. The sample was bleached with a sodium hypochlorite solution, which proved to be simple, rapid and highly effective. Calculation of irradiance distributions was studied for cases of stratified water with a diffusely reflecting bottom. The 2 stream method of solving the radiative transfer equation was adapted to the calculation of light distribution in vertically homogenous water bodies. The solution in such cases can be given in analytical form and will then allow study of the influence of various parameters (eg bottom reflectivity, ratio of diffuse to direct solar incoming radiance and inherent water optical properties) on the spatial distributions of the fluxes. This method was then extended to stratified water bodies consisting of homogenous layers, and could therefore be used in the estimation of errors in pigment retrieval when water stratification and bottom reflectance cannot be neglected.

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