• As the simulation is based on only a limi ted number of days, the dust load scaling is arbitrary. Taking 
this fact into account, the general shape of the two distributions agree remarkably well within a strip of 
about 1 km width along the road. In particular, this is evident from west-east and south-north dust load 
profiles averaged over 11 image columns and 11 rows (i.e. over 400 m), respectively. The orientation 
of south-north transects are close to the prevailing wind direction. In general, the agreement is better 
across the main wind direction than along that direction. 
s We found that within a strip of 400 m width along the road the satellite based dust load u is by a factor 
9.3 greater than the dust load u, t oek calculated on the basis of the stochastic model. This difference 
can be attributed to the different time interval involved. The satellite based value is assumed to be a 
measure for the deposition integral from the date of road construction to the date of the satellite image 
acquisition, i.e. from 1974 to 1987, whereas the the simulation covers only 65 days. Assuming a constant 
deposition rate over 13 years, a time corrected rescaling factor of about 9.3/(13'365.25/65) = 0.13 
results. This means that 87% of the dust deposited during 13 years disappeared below the vegetation 
canopy or was washed away from the leaves. 
• Apart from this application on a local scale, suspended dust may also be detected on larger scales, e.g. 
as volcanic ash, as tropospheric or stratospheric aerosols or desert sand. We believe that the satellite 
based method described in this paper is also potentially valid for quantifying pollutants of this kind. 
Satellite imagery is often the only way to detect and to quantify such long range phenomena. 
6 REFERENCES 
Frey, U., 1992. Private communication 
Guyot, G., 1989. Signatures spectrales des surfaces naturelles, Paradigme, Caen 
Lamprecht, R., 1989. Modeling air pollution dispersion with a Monte Carlo diffusion model. PSI General 
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Lamprecht, R., 1992. Modeling dry deposition of dust along the Dalton Highway. PSI General Energy 
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Lamprecht, R., Gräber, W M 1993. Modeling dry deposition of dust along the Dalton Highway. Sub 
mitted for publication in Implication for Ecosystem Response to Disturbance. A Case Study in Arctic 
Tundra. Ecological Studies Series, Springer, New York 
SPOT, 1987. SPOT User’s Handbook, Volume 1: Reference Manual, Volume 2: SPOT Handbook, Volume 
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Tanré, D., Deroo, C., Duhaut, P., Herman, M., Morcrette, J.J., Perbos, J., Des 
champa, P.Y., 1986. Simulation of the satellite signal in the solar spectrum (5S). Users Guide 
(revised 1987) 
Tanré, D., Deroo, C., Duhaut, P., Herman, M., Morcrette, J«J., Perbos, J., Des 
champa, P.Y., 1990. Description of a computer code to simulate the satellite signal in the solar 
spectrum: the 5S code. Int. J. Remote Sensing, Vol. 11, No. 4, pp 659-668 
TeiUet,P.M., Sanier, R.T., 1991. Altitude dependence in a semi-analytical atmospheric code. Proc. 5th 
Int. Colloquium on Physical Measurements and Signatures in Remote Sensing, 
Courchevel, France. January 14-18, 1991 (ESA SP-319,May 1991), pp 95-100 
7 ACKNOWLEDGEMENTS 
We wish to thank K. Seidel from the Swiss Federal Institute of Technology for making available the SPOT 
image and for his helpful discussions about the data handling. Additionally, we are indebted to P. Courrouyan 
and C. Ritter from SPOTIMAGE for their information on the calibration procedure. We express our appreci 
ation to U. Frey from the School of Technology at Rapperswil who performed the laboratory measurement of 
the dust reflectance. Finally we wish to thank D. Berlowitz for revising the english wording of the manuscript. 
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