It can be seen from Table II that the daily calculated mean 
reflectance factor of the four Landsat MSS bands varies within the standard 
deviation for a slightly rough (fine grained) asphalt cover (type Al). Similar 
results could be obtained for a fine grained concrete surface (type C4) as 
reported in Table III. Based on this result, the surface weathering process 
does not cause a significant change of the reflectance factor within a four 
months measurement period. This is probably also true for a surface with a 
distinct structure such as the concrete types Cl, C2, and C3. However, ideal 
data sets, pointed out in the preceding section, were not available to verify 
this statement. 
These results, described in this paper, demonstrate that slightly 
rough (fine grained) asphalt and concrete surfaces can be recommended as 
reference targets for atmospheric corrections of remotely sensed data and for 
intercalibration of ground, airborne, and satellite sensors since the 
reflectance factor of those targets does not vary significantly over a longer 
time period of four months. Those horizontally located targets were used with 
some success by Staenz (1978) to remove atmospheric effects (path radiance, 
transmission) from Landsat MSS data. 
CONCLUDING REMARKS 
From this investigation the following conclusions can be drawn: 
- For all the investigated targets (2 asphalt and 6 concrete types), 
the reflectance factor of the two visible Landsat MSS bands 4 and 5 
is lower than for the near infrared bands 6 and 7. Furthermore, it 
was found that different asphalt and concrete types have different 
reflectance factors. This is mainly due to the material 
composition, surface structure, weathering condition, etc. 
E Illumination/viewing geometry effects become more important as we 
move towards asphalt and concrete targets with a distinct structural 
surface (e.g. grooved targets). Also the target geometry which 
affects the amount of microshadowing near the illumination/viewing 
geometry should be taken into account for such investigations. 
= The surface weathering process does not influence the Landsat MSS 
band reflectance factor of less structural (slightly rough) targets 
within a four month measurement period. This indicates that the 
reflectance factor of such targets compared to a vegetated surface 
has not to be determined permanently with radiometric measurements 
or models and therefore, the use of those targets saves time and 
costs. Unfortunately, ideal data sets were not available to 
investigate this effect on more structural targets. 
= The utilization of asphalt and concrete surfaces without a distinct 
structure as reference targets can be recommended for 
intercalibration between ground, airborne and satellite data. 
However, it may be difficult to locate homogeneous field targets 
which have the required size of at least 3 by 3 pixels (e.g. Landsat 
MSS: 240x170 m2, Thematic Mapper: 90x90 m2, SPOT: 60x60 m2). 
ACKNOWLEDGEMENTS 
The active support of Dr. F. Fasler (State Bureau of Statistics, 
Canton, Aargau, Switzerland), the LAD of the Swiss Army, Radio Schweiz AG, and 
SWISSAIR throughout the data acquisition is gratefully acknowledged, as is the 
assistance of Dr. D.G. Goodenough and Dr. F.J. Ahern (Canada Centre for Remote 
Sensing, Ottawa) for critically reading the manuscript. 
314 
DATE 
25 May 
2 June 
28 June 
11 July 
8 Augu: 
24 Augu: 
15 Sept: 
DATE 
26 May 
2 June 
28 June 
11 July 
2 Augu 
24 Augu 
15 Sept