816 
Table 1 lists the various shutter speeds in terras of the length 
of time the shutter remained open for a common lens opening of 
f-5.6. Using the 1,500 feet pass as the reference, the relative 
film exposure for the 6,000 and 15,000 feet pass was calculated 
for each flight mission (Table 1). Since all shutter speeds used 
were within the range of 1/225 to 1/500 of a second, no reciproc 
ity problems that often cause departure of the dye emulsions 
sensitivities from the linear portion of the expected D-Log E 
curve when slow shutter speeds are used should exist (Kodak, 
1971). 
TABLE 1 
Shutter Speeds and Relative Film Exposures for 
Vegetation Study Using Infrared Film 2443 
Shutter 
Speeds for a f-5.6 Relative 
FlightLens OpeningFilm Exposure 
JUNE 
1,500 
feet 
.00250 
sec. 
1.000 
6,000 
feet 
.00200 
sec. 
0.800 
15,000 
feet 
.00167 
sec. 
0.668 
SEPTEMBER 
1,500 feet 
.00222 sec. 
1.000 
6,000 feet 
.00200 sec. 
0.901 
15,000 feet 
.00143 sec. 
0.644 
SOLAR INTENSITY AND REFLECTANCE MEASUREMENTS 
Solar spectral intensity was measured over a frequency range of 
500 to 900 nanometers with an Isco model SR spectrophotometer 
(Figure la, b)„ The leveled meter was located near the targets 
at an elevation of 1.2 meters and had an unobstructed sky view. 
Measurements were taken during each of the three flying height 
passes on both flight dates. Immediately after taking the solar 
intensity readings during each pass, a fiber optics sensor attach 
ment to the Isco spectrophotometer was used to measure the spec 
tral reflectance of the red and green targets from a distance of 
one-half meter above the rugs. 
To obtain the normalized relative reflectance curves (Figure 2a, 
b), the measured reflectance at the time of each pass was multi 
plied by the relative film exposure (Table 1) for each flight- 
altitude combination studied. This normalized relative reflec 
tance may be thought of as what the camera film would view if