Авторизоваться
Для зарегистрированных пользователей

The  analysis  of  two  years  of  Collection  3  and  five years  of  Collection  4  Terra  Moderate  Resolution  Imaging  Spectroradiometer (MODIS) Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation (FPAR) data sets is  presented in  this  article  with  the  goal  of  understanding  product  quality with  respect  to  version  (Collection  3  versus  4),  algorithm  (main versus backup), snow (snow-free versus snow on the ground), and cloud  (cloud-free  versus  cloudy)  conditions.  Retrievals  from  the main radiative transfer algorithm increased from 55% in Collection 3  to  67%  in  Collection 4   due  to algorithm  refinements  and improved  inputs.  Anomalously  high  LAI/FPAR  values  observed in Collection 3 product in some vegetation types were corrected in  Collection  4.  The  problem  of  reflectance  saturation  and  too few  main  algorithm  retrievals  in  broadleaf  forests  persisted  in Collection  4.  The  spurious  seasonality  in  needleleaf  LAI/FPAR fields was traced to fewer reliable input data and retrievals during the boreal winter period. About 97% of the snow covered  pixels were processed by the backup Normalized Difference Vegetation Index-based algorithm. Similarly, a majority of retrievals  under cloudy conditions were obtained from the backup algorithm. For these  reasons,  the  users  are  advised  to   consult  the  quality  flags accompanying the LAI and FPAR product