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INTRODUCTION 
In 1977, an atmospheric correction algorithm for Landsat MSS data 
was implemented in the image analysis software of the Department of Geography, 
University of Zurich (Fasler, 1978; Staenz, 1978). This atmospheric correction 
method is based on using non-vegetated natural surfaces as well as artificial 
surfaces as ground calibration test sites of known reflectance factor (Lyon, 
1975, Staenz, 1978). A water body (Lake of Zurich) was chosen as a dark 
standard, and asphalt/concrete. as a bright standard, respectively. Therefore, 
it is important to acquire a greater understanding of the optical properties of 
those standards and their changes as related to different parameters such as 
sun zenith angle, age, etc. 
Among several authors, Soerensen et al (1976), Ahern et al (1977), 
and Sturm (1977) have systematically investigated the reflective properties of 
lake water. Unlike the water body, only non-extensive studies are published 
about the reflectance characteristics of asphalt and concrete, so far. Steiner 
and Gutermann (1966) have reported results of a Soviet study on the reflective 
properties of different road surface types, mainly between dry and wet road 
conditions. Miller and Pearson (1971) collected reflectance measurements of 
common road surfacing materials to demonstrate how the target reflectance 
factor can change as a function of the weathering process. 
In this paper, a more detailed study undertaken by the Department of 
Geography during the summer of 1977 is described. The reflectance measurements 
were carried out with a Landsat MSS-compatible EXOTECH 100 radiometer to show 
the reflective characteristics of asphalt and concrete under various 
illumination conditions. Specific comparisons of the reflectance factor curves 
were also made to examine the influence of the weathering process. 
DATA ACQUISITION 
The radiometric field measurements were collected periodically at 
the tarmac of the Kloten airport near Zurich on seven different dates between 
May and September. A total of 380 Landsat MSS (EXOTECH 100 radiometer) spectra 
of eight different asphalt and concrete types as described in Table I were 
obtained in this time. Unfortunately, it was not possible to get the material 
composition of these horizontally located targets from the construction 
company. Therefore, only information about the surface could be made for this 
investigation. Simultaneously to the reflectance measurements, the following 
parameters were obtained: Time of observation, sun zenith angle, sun azimuth, 
viewing angle, and weather condition (temperature, humidity, cloudiness). 
INSTRUMENTATION AND MEASUREMENT PROCEDURE 
The reflectance measurements were carried out within the Landsat MSS 
bands using an EXOTECH 100 radiometer mounted on a tripod to look vertically on 
the targets (viewing angle J, = 09). For this platform, the 15° field-of-view 
objective lens of the radiometer were used, resulting in a circular target with 
a diameter of 0.4m at a tripod height of 1.5m. 
To normalize the collected radiance data, the total downwelling 
radiance reflected from a white standard was obtained before and after each 
measurement as described by Staenz (1978). The ratio of the radiance of each 
target to that of the reference, multiplied by the correction factor, gives the 
reflectance factor. This quantity is recommended by the Working Group VII-9 of 
the International Society of Photogrammetry for use in remote sensing (Boehnel, 
1977; Sievers and Kriebel, 1980). 
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