Geoscience Reference
In-Depth Information
2.4.2.4.
Validating the estimated vegetation index value
The French region of Franche-Comté is one of the regions in France for which
we have information relating to both its NDVI (calculated from satellite channels
within SPOT) and to its estimated quantitative index value, which is worked out
with the help of CLC. The fact that there are two sets of data makes it possible to
compare the results provided by each information source, and to validate (or not) the
estimation that is made by CLC. The NDVI explains the spatial temperature
variation reasonably well, particularly in summer when the index reaches a value of
-0.27 (which is represented by the dashed line in Figure 2.14). The correlation
coefficients, which are induced by the estimated index (created by CLC), and which
are represented by the full line in Figure 2.14, vary coherently with the NDVI. The
change in value of the coefficients from negative to positive can be easily explained
as follows: a significant amount of biomass that is present in an area has a high
NDVI (210-220) and a low estimated value that is calculated by CLC (-135). The
reverse situation is true for areas in which there is a low level of biomass, for
example in areas that are composed of artificial surfaces.
Figure 2.14.
Correlation coefficients between CLC index values
and the average temperature for each month of year
It should be noted that the weak winter coefficients have values that are in
contrast to the values of the summer coefficients, and this is particularly true for
July. With CLC the winter coefficients are much weaker. This fact shows that the
CLC does not take into consideration any of the minute variations that exist within
the different types of land cover. Figure 2.14 clearly shows that the index calculated
from CLC leads to the creation of an r-level which is much higher when the
correlation concerns the region of Franche-Comté (continuous line) rather than for
the whole of France (dotted line). Here we can see that vegetation has various
effects on temperature according to the different regions of France.
