1.1.5 Special Features of MERIS

The global mission of AATSR and MERIS make a major contribution to understanding the role of the oceans and ocean productivity in the climate system, and enhance our ability to forecast change through models. Both sensors offer a large synergistic potential that contributes to climate studies and global change observations in addressing environmental features in a multi-disciplinary way.

MERIS, primarily dedicated to observing oceanic biology and marine water quality through observations of water colour, makes also contributions to atmospheric and land surface related studies. AATSR has, besides its main objective to provide detailed sea surface temperature maps, the capability to measure a range of parameters for cloud microphysics, plus land surface temperature and various vegetation indices over land.

MERIS provides a unique European remote sensing capability for observing oceanic biology and marine water quality through global observations of ocean colour (figure 1.6), and provides continuity with other ocean colour sensors such as SeaWiFS and MODIS. AATSR provides continuity with similar ATSR instruments flown on ERS-1 and -2 ensuring the production of a near-continuous 15-year dataset of sea surface temperatures (SST) at an unprecedented accuracy level of 0.3 K or better (figure 1.7).

Figure 1.8 - Global ocean colour image

Figure 1.9 - An ATSR-2 11 µm brightness temperature image of the Gulf of California.

The hottest areas (shown in grey) are mostly land. The cooler sea surface temperatures are shown using purple (coolest) to red (warmest). Source: RAL (file: california_sst.gif).

Biogenic material in our oceans accounts for a large portion of their carbon pickup, playing a major role in the Earth's carbon cycle and therefore our climate. Sea surface temperature is one of the most stable of several geographical variables, which, when determined globally, characterize the state of the Earth's climate system. Phytoplankton concentrations in the oceans, responsible for the oceans' primary production, need to be known with a high degree of accuracy for their adequate prediction through modelling. Furthermore, the accurate knowledge of marine water constituent concentrations, has become mandatory for the assessment of the water quality in marine ecosystems. In parallel, the precise measurement of small changes in SST provides an indication of significant variations in ocean/atmosphere heat transfer rates and their impact on our physical climate.

AATSR and MERIS are both passive optical imaging instruments measuring radiation reflected and emitted from the Earth's surface. AATSR has 4 channels in the visible/near infrared wavelengths and 3 channels in the thermal infrared region. MERIS has 15 channels in the visible and near infrared (see table 1.1 below). The overlap between the instrument bands and the complementary measurements they provide over ocean and land, create novel opportunities for synergetic use of data in many fields of study.

Table 1.1 - MERIS spectral bands and applications.

This fixed set of bands was recommended by the Science Advisory Group (SAG). The level 2 ESA products have been validated for this set of bands.

The detailed spectral response of each band in each camera is given in document “MERIS Spectral Characterisation” ( R-10).