State of the art of image-aided navigation techniques for aircraft approach and landing
Résumé
Global Navigation Satellite Systems (GNSS) and Inertial Navigation Systems (INS) are currently the main navigation systems for aircraft. INS navigation is based on dead-reckoning principle so small errors in the measurements of vehicle accelerations and rotation rates can cause non-negligible integration drift. As an alternative navigation mean, more and more considered in navigation applications, image-aided inertial navigation is a complete autonomous navigation opportunity because it is only based on sensors onboard that provide information from the dynamic of the vehicle and the observation of the scenery. This system of navigation might be used in the particular case of loss of other systems of navigation that need additional exterior equipment (Global Navigation Satellite System (GNSS) or Instrument Landing System (ILS) for example). Besides in the particular context of civil aviation, during precision approaches (currently done with ILS or GPS augmented with GBAS or SBAS), it could be interesting to use an additional autonomous mean of navigation like video measurement that could overtake the need of additional ground or space infrastructure. But the performance has to be analyzed so as to determine if such a system can satisfy the precision approaches requirements which are very stringent. Development of techniques of navigation with imaging sensors does not mean a complete replacement of the currently widely used hybridization technique that consists in coupling Global Positioning System (GPS) with Inertial Navigation System (INS). Imaging sensors would be more an additional navigation means, to be combined with existing navigation means. Lots of studies concerning the use of visual measurements for navigation have been achieved and cover a large range of applications, from precise guidance of a UAV during a landing [5], to the estimation of translation or velocity between two successive image of the landscape [7]. From the review of the applications, one of the most robust solutions to use visual measurements is to extract some geometrical measurements from the detection of targets in the image and to use them in a Kalman filter with GPS and INS measurements [1]. The optimal solution would be to couple these geometrical visual measurements, obtained through the detection of particular features, with other means currently used on board (mainly INS measurements and GPS pseudo-range measurements). The information extracted by visual measurements can characterize precisely the relative position of the camera with respect to the feature detected in the image. However, the knowledge of a distance (range between camera and feature, height of camera above ground or dimension of an object on the ground) is needed to determine a metric scale which is absolutely needed to interpret the image measurements. The current paper proposes a state of the art of image-aided navigation methods. A description of the key elements or characteristics used in these methods is done. Based on this, a proposition is done for a video-based navigation system for approach and landing operations. This is a first step of feasibility study for an aircraft landing system based on video.
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