Curran, P.J., Dash, J., Lankester, T. and Hubbard, S.
Global Composites of the MERIS Terrestrial Chlorophyll Index
International Journal of Remote Sensing, 28, . (doi:10.1080/01431160600639685).
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From the year 2006, the European Space Agency (ESA) supported the production of the global composite (Level 3) of a unique terrestrial chlorophyll product called the MERIS Terrestrial Chlorophyll Index (MTCI) (Dash and Curran 2004). The MTCI is calculated using three red/near infrared bands of Envisat MERIS data (Rast et al. 1999). This index estimates the relative location of the reflectance 'red edge' of vegetation and is more sensitive than red edge position to canopy chlorophyll content, notably at high chlorophyll contents. This product effectively combines information on leaf area index and the chlorophyll concentration of leaves to produce an image of chlorophyll content (i.e. the amount of chlorophyll per unit area of ground). Chlorophyll content plays an important role in determining the physiological status of a plant, is related to photosynthetic rate and varies temporarily and spatially. MTCI global composites can be used to estimate relative and land cover specific, chlorophyll content in space and time and this in turn can be a key input to models of terrestrial productivity, gas exchange and vegetation health.
Two global monthly MTCI composites for March and August 2003 are presented on the cover. These images display the MTCI on a nominal scale of 0 to 6, with higher values indicating higher chlorophyll content. These images clearly capture the phenology of global vegetation. In March, a major part of the southern hemisphere (e.g. South Africa, South America) had high MTCI values during the peak of their growing season, whereas a major part of the northern hemisphere had low MTCI values in March. In August, the situation was reversed. A major part of the northern hemisphere (e.g. Europe, North America) had high MTCI values when the coverage of green leaves was at a maximum. In both images the tropical rain forests had relatively high MTCI values. It is interesting to note that even at the centre of these forests there is a change in MTCI values between March and August.
This global MTCI product will be produced as weekly and monthly composites and is the only terrestrial chlorophyll product available from space. The MTCI along with oceanographic chlorophyll concentration estimates, also from MERIS, can be used to generate a 'global chlorophyll map' for the estimation of global productivity.
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