Measurement of Line Characteristics and of Track Irregularities by Means of DGPS and INS

The evaluation of existing line characteristics and geometric track irregularities, being perhaps dangerous for dynamic safety of railway systems, becomes more and more evident with rising use of tilting trains like the German ICE3 or ICT, as the resulting irregularities may lead to the danger of train derailment. To identify track defects, a new approach of measuring technique using differential GPS and an inertial navigation system to determine the absolute position and ultrasonic devices to determine the peculiar properties of the geometric track quality was developed. By combination of differential GPS (DGPS) and inertial navigation system (INS) the position and the rigid body motions of a measurement platform at a self propelled draisine is determined. This platform is used additionally as a base for measuring the relative position of the left and right railhead vertically and laterally by ultrasonic sensors, so that their position can be described in an earth fixed co-ordinate system. The basic principles of this measurement system are explained as well as the results of railway field tests (together with the Austrian Railways̈ OBB) are demonstrated. An accuracy in the millimeter range has been proven. The speed of the measurement draisine was up to 50 km/h. Wavelengths of up to 200 m can be determined.