Mkb. Ludeke et al., THE USE OF SATELLITE NDVI DATA FOR THE VALIDATION OF GLOBAL VEGETATION PHENOLOGY MODELS - APPLICATION TO THE FRANKFURT BIOSPHERE MODEL, Ecological modelling, 91(1-3), 1996, pp. 255-270
An algorithm based on a three-spline function fitted to measured NDVI
courses (normalized difference vegetation index) was developed to anal
yze a given NDVI annual course with respect to leaf shooting and leaf
abscission times of deciduous vegetation. in contrast to algorithms wh
ich are based on modified second derivatives of the NDVI time course t
o detect shooting or abscission, the proposed algorithm takes into acc
ount the whole annual time course and is therefore less sensitive to n
oise in the NDVI-signal. In the present study this algorithm was used
to validate the phenology results for the deciduous vegetation of a gl
obal equilibrium run of the prognostic Frankfurt Biosphere Model (FBM,
spatial resolution 0.5 degrees x 0.5 degrees) driven by a climatology
which represents a mean seasonality of the driving variables. The mea
n value of the area-weighted frequency distribution of the difference
between the shooting date deduced from NDVI and the shooting date calc
ulated by the FBM for the deciduous vegetation types is -4 days, indic
ating that in the global mean the FBM predicts leaf shooting less than
one week too late. A 75% fraction of the area under consideration sho
ws predicted shooting dates lying within a range of +/- 30 days compar
ed to the satellite-derived dates. The distribution has its maximum at
a difference of 0 days (i.e. the FBM exactly fits the NDVI deduced sh
ooting day for these areas). This result supports the general assumpti
on that at least in global scale models phenology can be successfully
deduced from carbon flux balance considerations.