Dash, J. and Curran, P.J.
The MERIS terrestrial chlorophyll index
International Journal of Remote Sensing, 25, (23), . (doi:10.1080/0143116042000274015).
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The MEdium Resolution Imaging Spectrometer
(MERIS), one of the payloads on Envisat, has fine spectral
resolution, moderate spatial resolution and a three day repeat
cycle. This makes MERIS a potentially valuable sensor for the
measurement and monitoring of terrestrial environments at
regional to global scales. The red edge, which results from an
abrupt change in reflectance in red and near-infrared
wavelength has a location that is related directly to the
chlorophyll content of vegetation. A new index called the MERIS
terrestrial chlorophyll index (MTCI) uses data in three red/NIR
wavebands centred at 681.25nm, 705nm and 753.75nm (bands 8,
9 and 10 in the MERIS standard band setting). The MTCI is easy
to calculate and can be automated. Preliminary indirect
evaluation using model, field and MERIS data suggested its
sensitivity, to notably high values of chlorophyll content and its
limited sensitivity to spatial resolution or atmospheric effects. As
a result this index is now a standard level-2 product of the
European Space Agency.
For direct MTCI evaluation two different approaches were used.
First, the MTCI/chlorophyll content relationship were
determined using a chlorophyll content surrogate for sites in
southern Vietnam and second, the MTCI/chlorophyll
relationship was determined using actual chlorophyll content for
sites in the New Forest, UK and for plots in the greenhouse.
Forests in southern Vietnam were contaminated heavily with
Agent Orange during the Vietnam War. The contamination level
was so high that it led to a long term decrease in chlorophyll
content within forests that have long since regained full canopy
cover. In this approach the amount of Agent Orange dropped on
to the forest between 1965 and 1971 was used as a surrogate
(inverse) for contemporary chlorophyll content and was related
to current MTCI at selected forest sites. The resulting
relationship was negative. Further per pixel investigation of the
MTCI/Agent Orange concentration relationship is under way for
large forest regions. In the second approach MTCI was related
directly to chlorophyll content at two scales and the initial
resulting relationships were positive. Further plans involve the
evaluation of the MTCI at local, regional and eventually global
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