Small et al. [2010] reported that GPS noise statistics, specifically MP1 (MultiPath error on the L1 frequency), are anti-correlated with NDVI (Normalized Difference Vegetation Index).  Shown above are daily MP1 values in blue and 16-day MODIS NDVI values in green for Plate Boundary Observatory GPS site P422 (photo at right).  The correlation between the two time series is 0.8 (days with snow have been removed). Results for site P022 are shown below.

Foothill, Idaho, PBO site P422

La Grande, Oregon, PBO site P022