OBSTACLE AWARENESS AND COLLISION AVOIDANCE RADAR SENSOR SYSTEM FOR LOW-ALTITUDE FLYING SMART UAV Young K Kwag and Jung W Kang, Avionics Dept. AERC, Hanhk Aviation University, Seoul, Korea Abstract In this paper, the critical requirement for obstacle awareness and avoidance is assessed with the compliance of the equivalent level of safety regulation, and then the collision avoidance sensor system is presented with the key design parameters for the requirement of the smart unmanned aerial vehicle in low-altitude flight. Based on the assessment of various sensors, small-sized radar sensor is selected for the suitable candidate due to the real-time range and range-rate acquisition capability of the stationary and moving aircraft even under all-weather environments. Through the performance analysis for the system requirement, the conceptual design result of radar sensor model is proposed with the range detection probability and collision avoidance performance in a typical flight environment. Introduction Recently, Unmanned Aerial Vehicle (UAV) has been drawing a great attraction for the applications to both civil and military mission without risk in air safety for the pilot flying in low- altitude and/or in dangerous battlefield environment. Due to the inherent nature of the low flying vehicle, obstacle awareness is a fundamental requirement to avoid the collision against stationary and/or moving target obstacles along the flight path. Also it is noted that UAV should secure the equivalent level of safety comparable with manned aircraft in order to fly in civil and military airspace. Thus the collision avoidance system should be considered as a part of the navigation system in an unmanned vehicle. The obstacle awareness and collision avoidance is being acknowledged as the most important issues in the field of unmanned vehicle. An international standard regulation for the “sense-and-avoid” of UAV is being studied in Europe and USA, and the related technology has not been matured yet for the unmanned systems application. Recent technology advances in obstacle detection using optical imaging sensor for aircraft [I] and laser radar for helicopter [2] have been addressed in the articles, but the radar sensor technology for obstacle awareness and collision avoidance is being under development [3]and has recently been demonstrated for the manned helicopter and unmanned vehicle [4]. Most of current collision avoidance system of the manned aircraft employs Traffic Alert and Collision Avoidance System (TCAS) with standard protocol, which measures relative range and range rate of intruding aircraft using interrogation method and provide the decision information to the pilot for the flight control autonomously [SI. ADS-B (Automatic Dependent Surveillance-Broadcast) is being considered for the future collision avoidance system, which broadcast own GPS-based flight position information to the pass-by aircrafts in order to secure the sufficient distance around own aircraft [6]. But many aerial vehicles, especially MAVs and UAVs can not afford to cany too many avionic aids due to the weight, volume, power, and even cost constraints. Thus, collision avoidance strategies require minimal avionic aids and effective performance with small-size and light-weight for the pilot and even for automating the task of collision avoidance in low altitude pilotless aerial vehicles. In addition, collision avoidance system should autonomously sense the obstacles along the flight path and measure the range and range-rate in real-time under the all-weather environments. The collision awareness and avoidance system is under feasibility study for the Korea Smart UAV project, whose objective is to develop a smart UAV capable of high speed cruise and vertical take- ofUlanding (VTOL) by integrating “smart” technologies over the years, funded by the Ministry of Science and Technology. The basic system requirement includes max. speed of SOOKm/h, altitude of 3 Km, endurance time of 3-5 hours, and obstacle detection range of more than 5 Km. sensor for collision avoidance are compared and the requirement for the radar sensor is assessed in terms In this paper, the characteristics of candidate 0-7803-8539-X/04/$20.00 0 2004 IEEE 12.D.2-1 Authorized licensed use limited to: University of North Carolina at Charlotte. Downloaded on January 19, 2009 at 13:41 from IEEE Xplore. Restrictions apply.of the system requirement and air safety regulation. Radar sensor-based obstacle awareness and collision avoidance system is proposed with the radar design parameters and avoidance criteria. Finally, the millimeter radar detection performance and the collision avoidance algorithm are presented for the application to the unmanned vehicles in the typical flight environments Micro MMW Condition wave Mode Active Active Wavelength cm cm Characteristics of Collision Avoidance Sensor System In general, the collision avoidance system for the manned and/or unmanned vehicles can be divided into cooperative system and non- cooperative system. The examples of the cooperative system include TCAS, ACAS, which currently is equipped with the general manned aircraft, and ADS-B is not dedicated for the collision avoidance system, but is under consideration for the future application. Non- cooperative system employs the sensors such as electro-optical sensor and electromagnetic radar sensor to measure the avoidance information of the obstacles using active or passive metbod. receives the reflecting energy, while passive sensor only receives energy radiated from obstacles. Depending on the type of applicable sensor, there are a number of advantages and disadvantages in terms of operating frequency, average power consumption, detection range, component size, angular resolution, atmospheric effects, clutter characteristics, and electromagnetic interference immunity. Due to the limited Capability of measuring the real-time range, the passive sensor is not considered for the candidate comparison. The frequency band of the microwave radar sensor is relatively low, so it does not provide the sufficient angular resolution, but is insensitive to the weather situation. On the other hand, the millimeter wave radar provides the advantages of the small-size, fine angular resolution, but it is limited to detection range and is sensitive to weather environment. Angular resolution may be improved by increasing the operating frequency, but is physically
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