Because of the spatial-temporal variability and inhomogeneity of natural factors and the uncertainty of human activities, runoff and sediment yielding is a complicated nonlinear process.

Due to the strong spatial inhomogeneity and temporal variability of atmosphere, especially water vapor , accurate modeling of path delay in GPS signals is necessary for high -accuracy position.

The results of our study showed, that there was a strongly spatial and temporal variability in the sward height and herbage allowance.