A GBAS Testbed to Support New Monitoring Algorithms Development for CAT III Precision Approach

Kurzfassung

The development of new monitoring algorithms needs to have access to a platform that offers flexibility, operational evaluation facilities, test and validation capacities. DLR’s GBAS test bed offers all these features with additional simulation capability. This paper illustrates these properties by showing an application of the recently developed absolute ionosphere gradient monitor by taking advantage of a network of three reference receivers located in the DLR’s research airport at Braunschweig. This paper presents a first draft of an absolute ionosphere gradient monitor capable of detecting gradients from 300 mm/km to 2000 mm/km in order to fulfill the GAST-D requirements in terms of ionospheric gradient monitoring for the ground subsystem. The three receivers give the possibility to build two independent Absolute Slant Ionosphere Gradient Monitors (ASIGM). The performances achieved depend on the performances of the receivers, their relative location and the orientation of their baselines with respect to the runway direction. ASIGM with baseline in the direction of the runway provide the best observability of an ionsphere gradient that a GBAS user can experience during the approach phase (for straight-in approaches). The smaller the angle between the runway and the considered monitor baseline is, the lower the uncertainty of the gradient in the direction of the runway. Distribution of receivers parallel to the runway provides the best observability conditions. This paper gives the optimal relative location of receivers in order to achieve 100% detectability in the 300 to 2000 mm/km range of the absolute slant ionosphere gradient. Two configurations were investigated: one with 3 and another one with 4 receivers linearly distributed. The results obtained are extremely promising for the GAST-D requirements fulfillment and the corresponding architectures can easily be implemented.