the sample variance for the hand-held and fixed data sets. Because of the similarity in the sample variance it is 
thought that any difference in the mean reflectance is coincidental. 
Wavelength (nm) 
Figure 8 . Mean reflectance of the grass surface measured using the sensor hand-held compared with it 
fixed to a support. 
Wavelength (nm) 
Figure 9. Coefficient of variation corresponding to figure 8 . 
For the grass, the mean of the hand-held data set showed no significant difference between the 
two methods in visible wavelengths, and the spectra were within the error limits in the near infra-red also. The 
sample variance for the two data sets reveals some spectral difference, with the variance of the hand-held series 
being lower in visible wavelengths but higher in near infra-red wavelengths than the variance of the fixed data 
set. The cause of this is unclear at present.