<title>MMW-radar-based navigation: solutions to the vertical position problem</title>

Abstract

The acquisition of navigation data is an important upgrade of enhanced vision (EV) systems. E.g. the position from an aircraft relative to the runway during landing approaches has to be derived from data of the EV sensors directly, if no ILS or GPS navigation information is available. Due to its weather independence MMW radar plays an important role among possible EV sensors. Generally, information about the altitude of the aircraft relative to a target ahead (the runway) is not available within radar data. A common approach to overcome this so called vertical position problem is the use of the Flat Earth Assumption, i.e. the altitude above the runway is assumed to be the same as the actual altitude of the aircraft measured by the radar altimeter. Another approach known from literature is to combine different radar images from different positions similar to stereo and structure from motion approaches in computer vision. In this paper we present a detailed investigation of the latter approach. We examine the correspondence problem with regard to the special geometry of radar sensors as well as the principle methodology to estimate 3D information from different rage angle measurements. The main part of the contribution deals with the question of accuracy: What accuracy can be obtained? What are the influences of factors like vertical beam width range and angular resolution of the sensor relative transformation between different sensor locations, etc. Based on this investigation, we introduce a new approach for vertical positioning. As a special benefit this methods delivers a measurement of validity which allows the judgement of the estimation of the relative vertical position from sensor to target. The performance of our approach is demonstrated with both simulated data and real data acquired during flight tests.