230 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
COTTONWOOD ( Populus deltoides , Bartr.) 
w 25 
FOLIAGE REFLECTANCE AT 600 fm » 
af 20 
LOWER SURFACE /" / 
PERCENT RE 
(RELATIVE 
? 
UPPER SURFACE 
INCHES 
15 ' 15 ' 15 1 15 1 15 ‘ IS ' 
MAY JUN JUL AUG SEP OCT 
READILY AVAILABLE MOISTURE 
^ y^^^^m^THE UPPER 30" OF SOIL. 
to 3 
X 2 
z 1 
1—^~T 1 1 1 i 1 1 1 
RAINFALL 
>» 
^ 600 
**jj 400 
Б 200 
E ° 
INCOMING SOLAR RADIATION 
ft ; 
15 1 15 1 15 1 15 1 15 1 15 
MAY JUN JUL AUG SEP OCT 
1961 
Fig. 5. Light reflectance at 600 millimicrons, 
available soil moisture in the upper 30 inches 
of soil, rainfall, and incoming solar radiation 
during 1961 for a Populus deltoides plantation 
at Urbana, Illinois, U.S.A. 
SYCAMORE ( Plontonus occidentolis , L.) 
Fig. 6. Light reflectance at 600 millimicrons, 
available soil moisture in the upper 30 inches 
of soil, rainfall, and incoming solar radiation 
during 1961 for a Liriodendron tulipifera plan 
tation at Urbana, Illinois, U.S.A. 
stronger than reflectance changes associated with decreasing available moi 
sture. 
Chemical analyses of chlorophyll content of the foliage made during 1961 
tend to support the association of increasing reflectance with the fall color 
change for all wavelengths between 550 and 690 millimicrons. Unfortunately, 
irregularities in the chlorophyll analyses discovered during the 1962 field 
season create some question as to the validity of this data. For this reason the 
chlorophyll analyses will not be discussed in more detail. 
Significance of Results 
The changes in light reflectance observed in the pine and broadleaved trees 
included in this study suggest that tone contrast between pine and broad 
leaved trees is easiest to obtain in the early spring. The two panchromatic/ 
minus-blue photographs shown in fig. 7 illustrate this. 
It appears that readily available soil moisture, and associated moisture 
stress in plant tissue, may be significant factors in determining the amount of