266 
* Nitrogen: it is the chemical compound which is best correlated with reflectances. With exception of 
X=1982nm, best correlations occur at wavelengths associated to absorption bands. The two reflectance ratios 
(i.e. p/pi68o P/P 2230 ) produce different results: p/p 16S0 tends to be efficient for wavelengths between 
1722nm and 1759nm, whereas the ratio p/p 2 23 o tends to be efficient for wavelengths between 1982nm and 
2190nm. This dual behaviour was also noticed for the other chemicals (L, Cell. W, Cell. S). 
* Lignin: correlations are relatively large. Best correlations were obtained for wavelengths between 1680nm 
and 1778nm, and for 2310nm. However, most of these wavelengths cannot be attributed to lignin. The fact 
that large correlations tend to occur at the same wavelengths for lignin and nitrogen can partly be explained 
by the large correlation between these two compounds (Table 1). 
♦Cellulose: cellulose concentrations, especially Cell.S, were poorly correlated with reflectances. Best 
correlations were obtained with attributable wavelengths. 
III. Laboratory-derived Predictive Equations 
Stepwise regression analysis was applied to laboratory-derived reflectance spectra for determining those 
spectral bands, and associated linear relations, that are predictive of chemical concentrations. Only reflectance 
data associated to the 13 spectral bands outside atmospheric absorption bands were considered. In addition to 
the raw reflectance p, regression analysis was also applied to several transformations of reflectances. The most 
successful were: log(l/p), p/p 168 o> and p/p 2 23 o- Two criteria were used for selecting "predictive wavelengths", 
and associated predictive linear relations: Fisher-Snedecor values larger than the tabulated F-value at a 1% 
significance level, and larger correlations between actual and predicted concentrations. Several predictive 
wavelengths were determined. Table 2 displays the most successful wavelengths and associated correlations 
between the predicted and actual chemical concentrations. It should be noted that: 
- two to three wavelengths were sufficient for predicting N, L and ADF concentrations with correlations larger 
than 97%, 87% and 84%, respectively. Results for cellulose S are much poorer than for cellulose W. 
- selected predictive wavelengths could not always be attributed to absorption bands of compounds. This could 
partly be explained by some intercorrelation between chemicals. This was typically the case with NDF: most 
predictive wavelengths that were selected correspond to absorption bands of nitrogen and protein. 
P 
log(l/p) 
P/PtôSO 
P / P2230 
N 
2180*-2230: 97 
2180*-2230: 97 
2180*-2270: 97 
2180*-2270: 97 
2190*-2270: 97 
L 
2190-2230: 88 
2180-2230: 88 
2180-2230: 88 
2190-2270*: 87 
1734-1722*-2270*: 89 
2190-2270*: 87 
ADF 
2100*-2230: 85 
1778*-1982: 84 
1982-1759-1722*: 88 
2230-2190: 88 
2230-2100*: 85 
1778*-1722*-1982: 88 
2190-2270*: 82 
2180-2270*: 82 
1982-1778*: 80 
1734-2270*-1722: 85 
2190-2270: 83 
2180-2270: 82 
2100*-2270: 80 
1982-1734-1722*: 84 
CellS 
2100**2230: 50 
2100*-2230: 49 
2270*-2100*:49 
2100*-2270*: 49 
CellW 
1722*-2230: 82 
1722*-2100*: 82 
1722*-2270*: 82 
1722*-2100*: 83 
1722*-2270*: 82 
1722**2230: 82 
1734*-2100*: 76 
1759-2100*: 73 
1734*-1982-2100*: 86 
1759-2100*-2270*:82 
1734*-l778*: 70 
2190-2270*: 67 
1734*-1778*-l 982: 82 
2270*-2190-2139: 77 
Hemi 
2139-2100*: 58 
2100*-2139-2230: 68 
2139-2100*: 58 
2100*-2139-2230: 68 
2190-2100*: 59 
2139-2100*: 59 
2139-2100*-2270*: 66 
1734-2270*-2100*: 68 
2139-2100*: 57 
2190-2100*: 62 
2139-2100*-2270*: 67 
NDF 
1734*-1759: 84 
2180-2230: 85 
2180-1982: 84 
1734*-1759: 84 
2180-1982: 84 
2190-1982:84 
2139-2270: 82 
2270-2190: 82 
1734*-l 722*-2100*:85 
1734*-l722*-2190: 85 
2180-1982: 82 
1734*-1778-1722: 85 
Table 2 : 
Optimal wavelengths 
in order of selection, 
from stepwise 
regression analyses on 
pine needle laboratory 
reflectance spectra 
with associated 
correlations (F>1%). 
Attributable 
wavelengths, i.e. 
within lOnmofa 
known absorption 
wavelength for that 
compound, are 
indexed with 
The relationships predictive of lignin, ADF and nitrogen concentrations mentioned below are represented in 
percentage of dry matter. Wavelengths that can be attributed to chemicals are indexed with the symbol *.