Global Monthly Vegetation Cover

Data Processing Description

Introduction Page, Preface

The processing of weekly data (B3.0/W15 --> B3.2/W15) was based on the GVI weekly composite raw (counts) data -- the Second Generation of GVI -- and is described in the NOAA Global Vegetation Index User's Guide (Kidwell 1997b) and in Gutman et al. 1995.

The monthly processing (B3.2/W15 --> C3.2/M15) flow included the following steps: 1) Quality/Cloud flags were applied on a weekly basis, resulting in data gaps, 2) NDVI was averaged over one month (five weekly composites) for each map cell to partially fill in the data gaps and reduce some of the angular variability (the weeks that spill over into the next month were used for both the current and the previous months); 3) bi-linear spatial interpolation was applied to the missing data areas with persistent cloudiness in monthly averaged images; 4) 3x3 map cell running average smoothing was done to partially account for the imperfection of cloud screening, to filter out atmospheric and angular variabilities, and to compensate for different numbers of observations used in monthly averaging and for random spatial sampling from the original Global Area Coverage (GAC) AVHRR data into the GVI map cells.

Note that the NDVI data were produced from the top-of-the-atmosphere radiances, i.e., no angular/atmospheric corrections were applied except for cloud screening.