Requirements for spaceborne traffic measurement based on the satellite TERRASAR-X

Abstract

With new methods, strategies and systems of intelligent transport management the continuous increasing traffic has to be opposed to reduce its negative effects. The safety has to be improved and the number of casualties has to be reduced. Congestions should prevent for keeping emissions of noise and air pollution acceptable. Basis of all immovative management strategies are reliable on traffic flow data. to improve the database significantly is the aim of a lot of current projects around the globe. The development of traffic counts, probe vehicle, and remote sensing are the most important topics in this context. The Institute of Transport Research of the German Aerospace Center (DLR) is developing a procedure to measure traffic flow parameters using the low earth orbit radar satellite TerraSAR-X. The SAR-sensor has some advantages over optical sensors: The procedure is independent of daylight or weather conditions and it is possible to detect cars an measure their speed in one and the same detection. But there are also some disadvantages because the processing of SAR-data is very complex and it is not possible to say if the requirements of modern intelligent transport management systems could be fulfilled by SAR-sensors systems. This paper shows a proposal how to define the requirements of intelligent transport systems (ITS) for satellite based traffic flow measurement. for defining this requirements four different factors have to be analysed: - possible applications, - mathematical analysis, - applicable regulations and relevant laws, and - important user groups. For analysing the applicable regulations not only national law and orders will be account. It would be a system for cross boarder data collection (a low earth orbit satellite system is global available) and therefore international regulations has to be analysed too. The global availability is one of the major advantages of such a space borne system. Most of the individual parameters are depending on different applications. Therefore it is important to have a close look on these traffic applications. The share of the satellite system for each application has to be analysed. There are already a lot of mathematical analysis's dealing with local and instantaneous traffic flow measurements. The most important will be shown. But there are also new studies dealing with the potential of measured traffic density. Each car and herewith each platoon of cars can be measured. This is much more detailed information than current traffic detectors can realize. In this context also the detection fault rate has to be analysed. There are a lot of telematic application and also different traffic management systems. All of them with its special user groups have to be analysed. It is not realistic to operate all possible application with such a system for traffic flow measurements therefore a ranking based on the best benefit for the important user groups is helpful. In a final abstract the most important factors and parameters will be shown with its definition in accuracy and availability.