Positioning of unmanned air vehicles by using continuously monitoring reference stations

Unmanned Air Vehicles have become one of the indispensable tools of industry and public sector in recent years. Althogh Unmanned Air Vehicles, initially started to use in military area, it is now used in archeology, agriculture, identification of forest areas, disaster management and in map construction. By using CORS Technique in surveying, more precise positioning measurements can be observed with only using one fixed GPS, and also these measurements can be done in wider coverage areas. When the photogrammetric mapping made by the UAVs compare with photogrammetric mapping made by airplanes, UAVs are faster, more precise, more cost-effective and have oppotunity to make repetitive measurements. Besides these advantages, there are also some disadvanteges which are the short duration of flight time, more affected by the the wind and disconnection of the radio link between the GPS antenna and the ground station during flight time. When we combine the benefits provided by the use of CORA with the use of CORS Technique, it will be faster and less costly to obtain the final products, and more accurate products will be obtained than with the measurements made with the airplane. All air vehicles have a GPS receiver to determine their position and direction. In addition to its GPS receiver, the UASTURK unmanned aerial vehicle was also equipped with a dual-frequency RTK GPS receiver for measuring with CORS Technique. By this way, we made a comparison of the GPS device on the plane and the equipped RTK GPS device. In our experiment, in the event of a radio link failure between the UAV and the Ground Control Station, the entire flight must be redone, for this reason an office evaluation method was used to eliminate radio link failure. With this method, the GPS datas recorded on the default GPS receiver and on the equipped RTK GPS receiver were corrected using past datas from the CORS station in the same time slot. First, the center coordinates of all the photographs were calculated by the corrections made for the RTK GPS receiver, and first orthomosaic product was produced. The same process was also performed using the GPS receiver on the UAV and second orthomosaic product was produced. Coordinate accuracy analysis of the orthomosaic products were made by 17 ground control points used in the field. As a result of this analysis, first orthomosaic product (RTK-GPS corrected) has centimeter level accuracy (10.7 cm horizontal - 26.9 cm vertical) and the second orthomosaic product (UAV-GPS corrected) has decimeter level accuracy (3.687 m horizontal - 3.194 m. vertical) If we consider that the coordinates calculated with the GPS-IMU system on board are accurate about 2-5 m, by this method the coordinates which observed by the measurement of UAV will be in the cm level.