SSgard {HydroMe} | R Documentation |
This selfstarting function estimates the water retention parameters contained in the Gardners function. It has an initial attribute that creates initial estimates of the parameters Thr, Ths, alp, and scal
SSgard(input, Thr, Ths, alp, scal)
input |
A numeric vector of the suction potential |
Thr |
A numeric parameter representing the residual moisture content |
Ths |
A numeric parameter representing the saturated moisture content |
alp |
A numeric parameter representing the inverse of air-entry potential |
scal |
A numeric parameter representing the pore-size distribution index |
The dataset should contain a column for logarithm of suction potential, taking care to place a very small numer for log (x) whenever x is zero. The function estimates the parameters in two parts: when the product of alp and input is less than or eaual to unity and when this quantity is geater than unity
numeric vector of the same length as input. It is the value of the expression Thr+(Ths-Thr)/(1+(alp*input^scal)) . It represents the fitted estimates of moisture contents using the Gardners model
If the model returns negative values for residual moisture content, a zero value should be dopted for that residual moisture content. Also, if the model fails to converge, one may need to adjust the controls. It is also important to note that some datasets do perform poorly with this function
Omuto, Christian Thine
Gardner, W.R., 1958 Some steady state solutions of the unsaturated moisture flow equation with application to evaporation from a water table Soil Science, 85, 228-232
SSvan, SSbrook, SScamp
##-- Load pfdata-- data(pfdata) gard.nlis <-nlsList(y~SSgard(x, Thr, Ths, alp, scal)|Level, data=pfdata) cor(fitted(gard.nlis),pfdata$y, use="complete")^2 # To compute r^2