First and Second Derivative

One of the methods to numerically calculate first and second derivative is to use Savitzy-Golay filter function. It is available in R in signal package. Function sgolayfilt may be used on all spectra with apply function. Order is set by m parameter (m=1 is the first derivative, m=2 is the second derivative etc.)

library(signal )
# first derivative by S-G filter
deriv1<-apply (a1,1 ,sgolayfilt,p=2 ,n=3,m= 1)
qplotspc(aggregate (deriv1, deriv1$explorder, mean) , mapping = aes (x =.wavelength, y = spc, colour= explorder ))+ scale_x_reverse()+ facet_grid(order ~ expl)
# second derivative by S-G filter
deriv2<-apply (a1,1 ,sgolayfilt,p=2 ,n=3,m= 2)
qplotspc(aggregate (deriv2, deriv2$explorder, mean) , mapping = aes (x =.wavelength, y = spc, colour= explorder ))+ scale_x_reverse()+ facet_grid(order ~ expl)