Learning-based monocular vision obstacle detection and avoidance for UAV navigation in urban airspace

• Main Author: Zhang, Yuhang
• Other Authors: Lyu Chen
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/169870
• Institution: Nanyang Technological University

Unmanned aerial vehicles (UAVs), also known as drones, have gained considerable interest among academics in recent years, which significantly increases the demand for autonomous navigation systems for UAVs. In this study, autonomous navigation is addressed as a two-stage problem. The first stage is the obstacle detection phase, during which the UAVs leverage their onboard sensors to perceive the surroundings and detect obstacles. The second stage is the obstacle avoidance phase, where the UAVs make decisions to continue operations without colliding with anything while approaching the target. This study proposes a self-supervised learning-based depth prediction framework as the criterion for obstacle proximity detection. The framework consists of two subnetworks: the depth and pose estimation modules. The former predicts depth values, while the latter evaluates the object’s translation and rotation matrix. The framework leverages the subnetworks’ outputs to reconstruct the projection relationships of pixels between adjacent frames to optimize the training process. To address the challenge of UAVs operating in large-scale environments, a modified loss function that combines photometric loss and edge-aware smoothness is presented to increase the depth prediction module’s accuracy. This study also presents a deep reinforcement learning-based obstacle avoidance system that takes depth maps as inputs to generate evasive maneuvers. The system works independently from priori maps and models while it learns the collision-free trajectory from interacting with the environment. This study deploys value-based algorithms to learn the nonlinear mapping between the continuous inputs and discrete output motion commands. Furthermore, the proposed system is validated on different simulation scenarios. It is capable of completing the obstacle avoidance task with relatively optimal trajectories in varied environments, demonstrating its superior effectiveness and transferability. Keywords: unmanned aerial vehicles, urban airspace, obstacle detection and avoidance, self-supervised learning, deep reinforcement learning.