THE PERFORMANCE ANALYSIS OF AN UAV BORNE VECTOR GRAVIMETRY SYSTEM

The integrated system based on Inertial Navigation System and Differential Global Navigation Satellite System (INS/DGNSS) has been proven to perform well in gravity estimation. Moreover, INS/DGNSS airborne gravimetry is a cost-effective system compared to satellite missions or terrestrial gravimeters. Although local gravity field can be surveyed by INS/DGNSS airborne gravimetry over small area in a relatively short time, there are some shortcomings of current commercial airborne system. The cost for renting an aircraft is high and the availability of conducting small area surveys is rather limited. In order to overcome these problems, an alternative presented in this study is based on the use of Unmanned Aerial Vehicle (UAV). Because high-accuracy Inertial Measurement Unit (IMU) and centimeter-level positioning are crucial in obtaining mGal-level gravity disturbance estimations, proposed UAV borne system loads a navigation grade IMU iNAV-RQH/RQT and a GNSS receiver by using an unmanned helicopter for positioning, orientation, and gravimetry. Based on the characteristics of vertical take-off and landing, in addition to the gravimetry in kinematic mode as the measure method, the Zero Velocity Update (ZUPT) mode is implemented as a novel method in the acquisition of gravimetry with proposed unmanned helicopter platform. This allows the system for correcting the drifts inherent in the IMU including accelerometers and gyroscopes. On the other hand, compared to the traditional approach for airborne scalar gravimetry, the algorithm for vector gravimetry determination is proposed in this study to estimate the gravity disturbance vector in all three components. The results in kinematic mode show that accuracies at crossover points are approximately 6-11 mGal and 4 mGal for the horizontal and vertical components, respectively with 0.5 kilometers resolution. The repeatability in ZUPT mode is evaluated with accuracies of about 2-3 mGal. Therefore, the capability of proposed UAV borne vector gravimetry system has been demonstrated through various scenarios in this study. Besides the classical DGNSS technique, the applicability of Precise Point Positioning (PPP) technique for INS/GNSS gravimetry is discussed.