The reference utilized for calibrating the measured radiance is -a 
panel coated with a matte cream white paint of 3M NEXTEL 3101. The calibration 
of the panel was conducted with the EXOTECH 100 radiometer measuring the total 
downwelling irradiance with the 27 -steradian field-of-view objective lens and 
the reflected panel radiance with the 15° field-of-view objective lens (Staenz, 
1978). The ratio of the reflected panel radiance to the total downwelling 
‘irradiance is the correction factor (reflectance factor of the panel) varying 
from 0.77 to 0.80 within the four radiometer bands. These calibration 
measurements were repeated several times during the measurement campaign to 
check the correction factor of the panel. 
EXPERIMENTAL RESULTS 
Typical asphalt and concrete Landsat MSS (EXOTECH 100 radiometer) 
reflectance factor curves, obtained from dry and weathered surfaces under 
similar illuminating (sun zenith angle 0; = 459, sun azimuth angle y; = 479) and 
viewing (9, - 09) conditions, are presented in Figure 1. The reflectance 
spectra indicate an increasing reflectance factor from band 4 to 7 for the 
concrete type C6. All the other investigated surface types show a slight 
decrease within the near infrared (band 6 to 7). The variation of the 
reflectance factor (5 - 35% in band 4, 6 - 40% in band 5, and 12 - 35% in band 
6 and 7) of these targets are due to its age (stage of weathering process), 
material composition, surface structure (target geometry) etc. as reported 
among others by Steiner and Gutterman (1966). 
The influence of the illumination and viewing geometry effects on 
the reflectance factor of asphalt and concrete surfaces can become very 
important as we intend to use those targets as a standard reflector over a 
longer period of time for corrections of atmospheric attenuation of satellite 
and airborne data as well as for intercalibration between ground, airborne and 
satellite sensors. Particularly data of sensor systems with wider scan angles 
and off-nadir viewing geometry (SPOT, airborne multispectral scanners) are 
40, 
7 C2 
C3 
w 
© 
A 
REFLECTANCE FACTOR Ry (%) 
no 
e 
1 | 
| | 
e e 
n ce 
  
  
  
-—— 04 
—A2 
0 T = 
4 5 6 7 
LANDSAT MSS BAND 
FIGURE 1: Reflectance factor Rp(%) of horizontally located asphalt (types Al 
and A2) and concrete surfaces (types Cl to C6) measured under 
similar illuminating and viewing conditions (sun zenith angle 0i 
= 45°, sun azimuth angle 0; 7 47°, viewing angle 0. m 09), For 
description of asphalt and concrete types see Table I. 
310 
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