AERIAL PHOTOGRAPHY AS A DATA SOURCE FOR TRAFFIC MANAGEMENT 
P.Hofstee, International Institute for Aerial Survey and Earth 
Sciences (ITC), Enschede (Netherlands) 
Introduction 
This paper has a limited scope: not all aspects of aerial photography 
as a data source for traffic management will be treated, but only a 
few selected main characteristics and problems, and two examples of 
practical applications will be discussed, 
As a technique, aerial survey has been applied in this field since 
1927. A wide range of applications has been reported (HOFSTEE, 1977), 
especially in the 60's and 70's. There seems to be, however, the 
phenomenon of underpublication: much knowledge and experience is not 
made generally accessible. 
Characteristics of aerial photography 
- The first main characteristic is timeliness: there is & high tem- 
poral correlation between data, as a large area is covered in a 
short time. There is, therefore, continuity in space, but sampling 
in time. Even when a number of overflights is made, the coverage 
is discontinuous in time. Traditional ground methods provide a 
contrasting situation: they usually give a continuity in time but 
sampling in space, as normally a number of points is selected where 
measurements (continuous for some time) are taken. 
— A second main characteristic is the possibility of simultaneous 
collection of several parameters; the aerial photograph can be used 
as a multi-purpose source. Traffic data and land use may be derived 
from the same aerial photograph, or speed, volume, headway and 
parking. As a consequence, several users may use the same data 
source: aerial photographs are a compatible source.