Robust UAV Position and Attitude Estimation using Multiple GNSS Receivers for Laser-based 3D Mapping (2312.02485v1)

Abstract: Small-sized unmanned aerial vehicles (UAVs) have been widely investigated for use in a variety of applications such as remote sensing and aerial surveying. Direct three-dimensional (3D) mapping using a small-sized UAV equipped with a laser scanner is required for numerous remote sensing applications. In direct 3D mapping, the precise information about the position and attitude of the UAV is necessary for constructing 3D maps. In this study, we propose a novel and robust technique for estimating the position and attitude of small-sized UAVs by employing multiple low-cost and light-weight global navigation satellite system (GNSS) antennas/receivers. Using the "redundancy" of multiple GNSS receivers, we enhance the performance of real-time kinematic (RTK)-GNSS by employing single-frequency GNSS receivers. This method consists of two approaches: hybrid GNSS fix solutions and consistency examination of the GNSS signal strength. The fix rate of RTK-GNSS using single-frequency GNSS receivers can be highly enhanced to combine multiple RTK-GNSS to fix solutions in the multiple antennas. In addition, positioning accuracy and fix rate can be further enhanced to detect multipath signals by using multiple GNSS antennas. In this study, we developed a prototype UAV that is equipped with six GNSS antennas/receivers. From the static test results, we conclude that the proposed technique can enhance the accuracy of the position and attitude estimation in multipath environments. From the flight test, the proposed system could generate a 3D map with an accuracy of 5 cm.

• The paper demonstrates a novel multi-GNSS approach using six antennas to accurately estimate UAV position and attitude without an IMU.
• It employs a Q-Method and hybrid fix solutions that enhance RTK performance, achieving 5 cm mapping accuracy even in multipath environments.
• Experimental tests validate that low-cost GNSS receivers combined with a laser scanner can produce precise 3D maps in both static and dynamic conditions.

Introduction

The utilization of small-sized Unmanned Aerial Vehicles (UAVs) for applications like remote sensing and aerial surveying has garnered substantial interest due to their cost-effectiveness and flexibility in operations. One of the critical aspects of these applications, particularly in direct 3D mapping, is obtaining accurate position and attitude data for the UAV. These are foundational for translating sensor data to a common coordinate frame, enabling the construction of precise maps.

Methodology

A novel technique for estimating the positions and attitudes of small-sized UAVs has been introduced, focusing on the use of multiple Global Navigation Satellite System (GNSS) antennas and receivers. This approach uniquely leverages the redundancy of multiple GNSS inputs to improve the performance of real-time kinematic (RTK) positioning, traditionally reliant on single-frequency GNSS receivers. Two primary strategies are employed: hybrid GNSS fix solutions and a consistency examination of GNSS signal strength.

This novel system involves outfitting a UAV with six GNSS antennas/receivers, resulting in an extended array and creating multiple possibilities for baseline vector estimations. An estimation approach, known as the "Q-Method," is utilized for calculating the optimal attitude from these vectors without necessitating an Inertial Measurement Unit (IMU), which generally adds to the cost and complexity of the system.

Experimental Results

Through static and flight tests, the proposed technique demonstrated its capacity to significantly refine the accuracy and reliability of UAV position and attitude estimations in multipath environments—areas with signal reflection and diffraction challenges. In static tests, the fix rate of RTK-GNSS solutions was notably enhanced, and multipath signals were effectively detected and mitigated.

In flight tests, the UAV's position and attitude estimates were successfully used to produce a 3D map with an accuracy of 5 cm. This impressive result was achieved using only GNSS receivers and a laser scanner, without the assistance of IMUs or other advanced sensors, which are often expensive and exceed the payload capacity of small UAVs.

Conclusion

The research demonstrates how incorporating multiple, low-cost GNSS receivers can yield precise and reliable UAV positioning and attitude estimation, even in challenging environments. This advancement could be pivotal in scenarios where direct 3D mapping is necessary but without the need for extensive groundwork or access to high-precision instruments, such as during the immediate aftermath of disasters. The system holds the potential for extensive use in various industries, bridging the gap between affordability and mapping accuracy.