The DG Performance Verifications of UAV Borne MMS Payload with Two Tactical Grade Low Cost MEMS IMUs Using New Calibration Method

摘要

Rapid spatial information collection has become an emerging trend for remote sensing and mapping applications. To facilitate applications such as environment detection and disaster monitoring, the development of rapid low cost systems for collecting near-real-time spatial information is very critical. The technology of Unmanned Aerial Vehicle (UAV) mobile mapping system (MMS) can satisfy these demands. It usually loads an Inertial Navigation System (INS) and Global Positioning System (GPS) for integrated positioning and orientation. Moreover, the mapping system is also loaded on board to implement of Direct Georeferencing (DG) capability. The DG capability can rapidly provide the coordinate of interesting points without any ground control points. These coordinates can be quickly converted to measurable spatial information for numerous applications demanding for near real time georeferenced images. This study develops a long endurance DG based fixed-wing UAV photogrammetric platform where a low cost tactical grade integrated Positioning and Orientation System (POS) is developed. In addition, a novel kinematic calibration method including lever arms, boresight angles and camera shutter delay is proposed. A commercial Micro Electro Mechanical Systems (MEMS) tactical grade IMU is also applied for comparison. Two flight tests with two tactical grade low cost MEMS IMUs are performed to verify the positioning accuracy in DG mode without using Ground Control Points (GCPs) using different calibration method. This study develops a new two-step-kinematic calibration method and compares with traditional two-step calibration. Furthermore, the performance of DG is also analyzed based on the two methods with the different flights and two DG modules. The results presented in this study indicate the accuracy of DG can be significantly improved by lower flight and hardware with superior specifications. The new two-step-kinematic method improves the accuracy of DG about 1-10%. The preliminary results show that horizontal DG positioning accuracies in two-dimension (2D) are around 8 m at a flight height of 600 m with the newly designed tactical grade integrated Positioning and Orientation System (POS). The positioning accuracy in three-dimension (3D) is less than 12 m. Such accuracy is good for near real-time disaster relief. The DG ready function of the proposed platform guarantees mapping and positioning capability even in GCP free environments, which is very important for rapid urgent response for disaster relief. Generally speaking, the data processing time for the DG module, including POS solution generalization, interpolation, Exterior Orientation Parameters (EOP) generation, and feature point measurements, is less than one hour.