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The DG performance verifications of UAV borne MMS payload with two tactical grade low cost MEMS IMUs using new calibration method
Abstract
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. Copyright
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To facilitate applications such as environment detection or disaster monitoring, the development of rapid low cost systems for collecting near real time spatial information is very critical. Rapid spatial information collection has become an emerging trend for remote sensing and mapping applications. In this study, a fixed-wing Unmanned Aerial Vehicle (UAV)-based spatial information acquisition platform that can operate in Ground Control Point (GCP) free environments is developed and evaluated. The proposed UAV based photogrammetric platform has a Direct Georeferencing (DG) module that includes a low cost Micro Electro Mechanical Systems (MEMS) Inertial Navigation System (INS)/Global Positioning System (GPS) integrated system. The DG module is able to provide GPS single frequency carrier phase measurements for differential processing to obtain sufficient positioning accuracy. All necessary calibration procedures are implemented. Ultimately, a flight test is performed to verify the positioning accuracy in DG mode without using GCPs. The preliminary results of positioning accuracy in DG mode illustrate that horizontal positioning accuracies in the x and y axes are around 5 m at 300 m flight height above the ground. The positioning accuracy of the z axis is below 10 m. Therefore, the proposed platform is relatively safe and inexpensive for collecting critical spatial information for urgent response such as disaster relief and assessment applications where GCPs are not available.
An approach to enhance the performance of tightly coupled GPS/INS systems is described. First, the advantages of tightly coupled systems compared to loosely coupled systems are clarified. Then, it is shown in hardware-in-the-loop tests and in a test drive that processing time differenced carrier phase measurements instead of delta-range measurements results in an increased velocity and attitude accuracy for the tightly coupled system, which is of great importance in the beginning of a time interval with purely inertial navigation, e.g. when GPS is lost due to jamming. A measurement equation is derived allowing to process the time differenced carrier phase measurements in the navigation Kalman filter. Finally, the proposed method is applied to missile navigation systems, where significant vibrations enter the inertial sensor data.
In this work the analysis of Inertial Navigation Systems (INS) is
approached from a control theory point of view. Linear error models are
presented and discussed, and their eigenvalues are computed in several
special cases. It is shown that the exact expressions derived for the
eigenvalues differ slightly from the commonly used expressions. The
observability of INS during initial alignment and calibration at rest is
analyzed. A transformation based on a physical insight is introduced
which facilitates the determination of the unobservable subspace and
states by inspection of the new dynamics matrix. Finally the
relationship between system observability and quality of estimation is
discussed.
Inertial navigation system (INS) and global position system (GPS) technologies have been widely utilized in many positioning and navigation applications. Each system has its own unique characteristics and limitations. Therefore, the integration of the two systems offers a number of advantages and overcomes each system's inadequacies. INS/GPS integration is usually implemented using Kalman filters. However, Kalman filters perform adequately only under certain predefined dynamic models and suffer from several problems related to observability and immunity to noise effects. An INS/GPS integration method based on artificial neural networks (ANNs) to fuse INS measurements and differential global positioning system (DGPS) measurements has been recently suggested. Although able to provide high performance INS/DGPS integration with accurate prediction of position components during GPS outages, the conventional methods of updating the ANN weights limit the real-time capabilities. This paper offers a new weight updating criterion to improve the limitation of traditional weight updating methods with the utilization of two different architectures; the position update architecture and position and velocity update architecture.
It is pointed out that the GPS (Global Positioning System) signal contains information which, when properly combined with information from INS (inertial navigation system) and other sensors, provides exceptionally high-accuracy position, velocity, attitude, and time information. These ten elements of information (three each in position, velocity, and attitude, and one in time) are common, in various combinations, to most of the avionics functions. When viewed from a system perspective, this high-precision information can be thought of as the integration basis, or a reference set, which offers opportunities for reconfiguration of the offensive, defensive, communication, navigation, and other sensors. Various integration architectures for fusion of these sensors can inherently enhance, enable, or severely limit these potential mission capabilities. The choice of integration architecture can directly and profoundly affect performance, cost of integration, cost of ownership, and exploitation of much greater mission capability. This is illustrated with the GPS/INS integration example