UNCERTAINTIES
Uncertainties are associated with all observations, including radiation
measurements. For example, vegetation heterogeneity can lead to
non-uniform radiation interception, and global radiation measurements
made under direct sunlight were found to be lower (about 10%) than
those above the canopy (Tuzet et al., 1997). On the other hand,
radiometer readings are greatly influenced by weather. For example,
water droplets on sensors can absorb long-wave radiation, resulting in
large deviations in long-wave radiation readings during rain or dewfall
events (Michel et al., 2008). This explains the relatively weak
relationship between RI and GPP at the daily scale. However, these
sensor-induced deviations are much less significant at the annual scale,
making the annual estimations of GPP more reliable.