220.127.116.11 Mission Objectives
The principal contributions of MERIS data to the study of the upper layers of the ocean are:
· the estimation of photosynthetic potential by detection of phytoplankton (algae);
· the detection of yellow substance (dissolved organic material);
· the detection of suspended matter (particulates and river-borne sediments);
Apart from the above three major observable features, it should also be possible to detect plankton blooms (for example red tides) through their absorption feature near 520 nm. In addition, investigations of water quality, the monitoring of extended pollution areas, and topographic observations (such as coastal erosion), should also be possible.
The radiation balance of the Earth/atmosphere system is dominated by water vapour, CO2 and clouds, as well as being dependent on the presence of aerosol. However, the global monitoring of cloud properties and their processes, is not yet sufficiently accurate. MERIS is intended to help redress this balance by providing data on cloud top height and optical thickness, water vapour column content, and aerosol properties.
Questions related to global change include the role of terrestrial surfaces in climate dynamics and biogeochemical cycles. Spatial and temporal models of the biosphere are currently being developed to study the mechanics of such complex systems in order to predict their behaviour under changing environmental conditions. These models are based on physical and biophysical relationships, which need to be estimated on a regular basis using data from spaceborne sensors. Repetitive accurate physical measurements are necessary in order to quantify surface processes and to improve the understanding of vegetation seasonal dynamics and responses to environmental stress.
To achieve these mission goals, the different radiometric and geometric requirements imposed by the various objectives have to be satisfied. With the help of the ESA Science Advisory Group for MERIS, these requirements have been refined, taking into consideration the constraints imposed by a polar orbiting platform and the technical possibilities of an imaging spectrometer.
In advance of the launch of MERIS, the Ground Segment was designed and algorithms were developed for the interpretation of MERIS observations, and dedicated studies are ongoing to establish the means of determining the accuracy of MERIS data products. This is achieved in close cooperation with the European Expert Support Laboratories whose scientists are the main authors for all information estimation algorithms. Wherever possible, the underlying physical models are being evaluated using experience acquired before ENVISAT launch using data provided by airborne or shipborne campaigns and in situ measurements on specially equipped campaign sites.