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infiltrometer
2011 Oct 11
1
singular gradient error in nls
...29.5, 31, 31.5, 32.5) #cumulative infiltration in cm per min
df <- data.frame(time, cumul)
df$cumul.m <- df$cumul/100/60 #convert to meters per second
df$time.s <- df$time*60 #convert to seconds
b2 <- 1-(0.196/(0.06/0.01131)) #relationship between soil moisture and the
size of the ring infiltrometer (6 cm radius by 113.1 cm2 cross sectional
area)
theta <- 0.196 #difference in residual soil water and field capacity
Here is the formula:
#Where a = K_fs and b=psi_f
nlsfit <-
nls(time.s~(theta/a*b2)*((cumul.m/theta)-(((0.16-b)/b2)*log(1+((cumul.m*b2)/(theta*(0.16-b)))))),
data = df, start...