# Using Ground-Based Passive Reflectors for Improving UAV Landing
## 1 Introduction  
The accidents analysis in military and civil aviation conducted by the International Civil Aviation Organization (ICAO) shows that about 70% of them occur during landing. Such a high level of accidents is due to the complexity of controlling the aircraft during landing [1], information and psychological overloads of the pilot (operator) controlling the landing procedure [2], and the need to simultaneously comply with a large number of restrictions [3]. The complexity of controlling the landing, and landing with a further ground roll, is predetermined by a fairly significant change in the aerodynamic properties of the aircraft during the landing process [4], due to the influence of the earth, the influence of the wind, and the very short time available for making a decision about entering the second circle that is re-landing [5, 6]. The influence of all these features is especially enhanced using unmanned aerial vehicles (UAVs), whose landing is carried out either without human participation in an automatic mode [7], or in manual and semi- automatic modes, with the participation of a human operator of the control point, who often remote a long distance away from the landing site [8]. The combination of all the above features determined the need to strengthen the automation of the landing process, and the development of special automatic landing systems [9, 10]. These solutions mainly took place along the way of creating ground-based radio landing equipment, based on the course-glide-landing control systems by radio beam [11] (radio zones). In such systems, the reference landing trajectory in the height (glide path) and in the horizontal plane (along the course) is created by the equisignal directions (zones), respectively, of the glide path and course beacons located near the runway [12]. The advantage of such systems is the simplicity of the information landing equipment onboard the aircraft, which should only determine the deviation of the aircraft from the reference trajectory in the vertical and horizontal planes. The disadvantages of ground landing facilities of this type are: the inability to automate landing until landing with a further ground roll, due to the distorting influence of theearth on the equi-signal directions; a long deployment time at a new location; the high cost of the system; the presence of a large number of maintenance personnel [13]. When landing on hard-to-reach and poorly developed territories, the problem of using sufficiently flat areas of the earth's surface, highway sections, etc., as airfields, is extremely urgent in the absence of stationary and mobile radio and lighting landing facilities [14; 15]. The rapid creation of such temporary airfields also makes sense near the sites of natural disasters (earthquakes, tsunamis, volcanic eruptions, hurricanes, etc. ), performing tasks to assess and eliminate their consequences. These features determine the need to develop simplified autonomous onboard landing systems that will ensure the landing of aircraft on radio-equipped airfields, without requiring a lot of additional preparatory work [16; 17].