MUNIR A , AVED A , BLASCH E . Situational awareness: techniques, challenges, and prospects [J ] . AI , 2022 , 3 ( 1 ): 55 - 77 . DOI: 10.3390/ai3010005 http://doi.org/10.3390/ai3010005 https://www.mdpi.com/2673-2688/3/1/5 https://www.mdpi.com/2673-2688/3/1/5 Situational awareness (SA) is defined as the perception of entities in the environment, comprehension of their meaning, and projection of their status in near future. From an Air Force perspective, SA refers to the capability to comprehend and project the current and future disposition of red and blue aircraft and surface threats within an airspace. In this article, we propose a model for SA and dynamic decision-making that incorporates artificial intelligence and dynamic data-driven application systems to adapt measurements and resources in accordance with changing situations. We discuss measurement of SA and the challenges associated with quantification of SA. We then elaborate a plethora of techniques and technologies that help improve SA ranging from different modes of intelligence gathering to artificial intelligence to automated vision systems. We then present different application domains of SA including battlefield, gray zone warfare, military- and air-base, homeland security and defense, and critical infrastructure. Finally, we conclude the article with insights into the future of SA.

WANG Z G , LIU B , CUI X G , et al . The application of micro coaxial rotorcraft in warfare: an overview, key technologies, and warfare scenarios [J ] . IEEE Access , 2022 , 10 : 40358 - 40366 . DOI: 10.1109/ACCESS.2022.3166890 http://doi.org/10.1109/ACCESS.2022.3166890 https://ieeexplore.ieee.org/document/9755973/ https://ieeexplore.ieee.org/document/9755973/

LAMAZARES Á , MOLINOS E , OCAÑA M . Detection and tracking of moving obstacles (DATMO): a review [J ] . Robotica , 2020 , 38 ( 5 ): 761 - 774 . DOI: 10.1017/S0263574719001024 http://doi.org/10.1017/S0263574719001024 https://www.cambridge.org/core/product/identifier/S0263574719001024/type/journal_article https://www.cambridge.org/core/product/identifier/S0263574719001024/type/journal_article Working with mobile robots, prior to execute the local planning stage, they must know the environment where they are moving. For that reason the perception and mapping stages must be performed previously. This paper presents a survey in the state of the art in detection and tracking of moving obstacles (DATMO). The aim of what follows is to provide an overview of the most remarkable methods at each field specially in indoor environments where dynamic obstacles can be potentially more dangerous and unpredictable. We are going to show related DATMO methods organized in three approaches: model-free, model-based and grid-based. In addition, a comparison between them and conclusions will be presented.

CAI W Y , XIE Q N , ZHANG M Y , et al . Stream-function based 3D obstacle avoidance mechanism for mobile AUVs in the internet of underwater things [J ] . IEEE Access , 2021 , 9 : 142997 - 143012 . DOI: 10.1109/ACCESS.2021.3119594 http://doi.org/10.1109/ACCESS.2021.3119594 https://ieeexplore.ieee.org/document/9568944/ https://ieeexplore.ieee.org/document/9568944/

WU J F , WANG H L , ZHANG M H , et al . On obstacle avoidance path planning in unknown 3D environments: a fluid-based framework [J ] . ISA Transactions , 2021 , 111 : 249 - 264 . DOI: 10.1016/j.isatra.2020.11.017 http://doi.org/10.1016/j.isatra.2020.11.017 Compared with preprocessed obstacle environments, unknown environments are more challenging for path planning. In unknown environments, an agent can make decisions only by relying on the obstacle information detected by its onboard sensors. However, when facing non-convex obstacles, this limited detection information can easily trap the agent in a local optimum. In this paper, a nature-inspired methodology called Interfered Fluid Dynamic System (IFDS) is extended to anti-local-optimum obstacle avoidance in unknown 3D environments for the first time and a novel fluid-based path planning framework is proposed. First, the detection region of the agent is discretized. Then, spherical virtual obstacles (SVOs) located at detected discrete points are generated and memorized. Thus, obstacle avoidance in unknown environments is transformed into the avoidance of known SVOs. Next, the currently generated and memorized SVOs are input to the core of the framework, the IFDS algorithm, to produce repulsive effects, and the corresponding 3D avoidance path is resolved. On this basis, to address local optimum in cases with non-convex obstacles, and considering compatibility with the IFDS, the direction coefficient and sink-heading angular rate adjustment strategies, which belong to the same system as the IFDS, are introduced to modify the IFDS in this framework. Finally, receding horizon control is introduced to improve the obstacle avoidance performance. Simulations show that the proposed framework can enable the agent to autonomously jump out of the 3D non-convex obstacle environments with typical features of the local optimum, including wall-like and cave-like obstacles, and safely reach the destination.Copyright © 2020 ISA. Published by Elsevier Ltd. All rights reserved.

ZHANG Z D , WANG Z J , YU J . Extended dynamic system modulation for real-time obstacle avoidance [J ] . Chinese Journal of Aeronautics , 2022 , 35 ( 12 ): 212 - 225 . DOI: 10.1016/j.cja.2022.01.007 http://doi.org/10.1016/j.cja.2022.01.007 https://linkinghub.elsevier.com/retrieve/pii/S1000936122000073 https://linkinghub.elsevier.com/retrieve/pii/S1000936122000073

CHAI R Q , TSOURDOS A , SAVVARIS A , et al . Review of advanced guidance and control algorithms for space/aerospace vehicles [J ] . Progress in Aerospace Sciences , 2021 , 122 : 100696 . DOI: 10.1016/j.paerosci.2021.100696 http://doi.org/10.1016/j.paerosci.2021.100696 https://linkinghub.elsevier.com/retrieve/pii/S0376042121000014 https://linkinghub.elsevier.com/retrieve/pii/S0376042121000014

邓海鹏 , 麻斌 , 赵海光 , 等 . 自主驾驶车辆紧急避障的路径规划与轨迹跟踪控制 [J ] . 兵工学报 , 2020 , 41 ( 3 ): 585 - 594 . DOI: 10.3969/j.issn.1000-1093.2020.03.020 http://doi.org/10.3969/j.issn.1000-1093.2020.03.020 为减少道路突发事故，提高车辆通行效率，需要研究车辆的紧急避障以实现自主驾驶。基于车辆点质量模型，设计了非线性模型预测控制（MPC）路径规划器；基于车辆动力学模型，设计了线性时变MPC轨迹跟踪器。在路径规划层引入避障功能函数，通过车辆与障碍物的距离调节函数值大小，综合避障函数权重和路径偏差权重，规划出一条既能避开障碍物又使路径偏差最小的临时轨迹。在轨迹跟踪层，利用该临时轨迹和航向角偏差作为车辆主动转向控制参考量，将线性时变MPC优化问题转化为二次规划问题，计算满足车辆动力学约束的前轮转向角最优解。结果表明：所设计的双层MPC紧急避障控制策略对低速(60 km/h)、中速(80 km/h)、高速(100 km/h)行驶车辆有很强的适应性，高速行驶时最大质心侧偏角不超过1.0°，最大航向角偏差不超过2.5°，车辆横向稳定性良好，随着车速增大，车辆避障响应时刻提前；在多车连续避障场景中，自主驾驶车辆的质心侧偏角和航向角偏差均能控制在较小范围内，在多目标连续避障的路径规划和轨迹跟踪问题上同样具有很好的控制效果。

DENG H P , MA B , ZHAO H G , et al . Path planning and tracking control of autonomous vehicle for obstacle avoidance [J ] . Acta Armamentarii , 2020 , 41 ( 3 ): 585 - 594 . (in Chinese) DOI: 10.3969/j.issn.1000-1093.2020.03.020 http://doi.org/10.3969/j.issn.1000-1093.2020.03.020 Emergency obstacle avoidance is one of the key points for autonomous driving system. A path planning controller based on non-linear model predictive control and a path tracking controller based on linear time-varying model predictive control are designed.In path planning controller，an obstacle-avoiding function is used to adjust the distance between the intelligent vehicle and obstacles by calculating the value of obstacle-avoiding function.A new route is supposed to be planned，which can not only keep away from obstacles but also decrease the deviations from the global course，by considering the different weights of obstacle-avoiding function and the planning error. In path tracking controller，the solution of linear time-varying model predictive control is converted into a positive-definite quadratic program.And then the desired steering angles of front wheel are calculated by using the reference trajectory and orientation angle of vehicle center. The results show that the obstacle-avoiding controller has strong robustness and the path tracking controller has better performance in controlling accuracy and vehicle dynamics stability when a vehicle travels at 60 km/h，80 km/h，or 100 km/h. The maximal side-slip angle is no more than 1°，and the maximal deviation of yaw angle is less than 2.5°.Obstacle avoiding action occurs in advance with the increase in velocity of autonomous vehicle. In addition，the dual-MPC controller is adaptive to the circumstance of multi-obstacles avoidance as well，which can be easily demonstrated by the small deviation of yaw angles and small side-slip angles.Key

TCHUIEV V , SHIMA T . Intercept angle guidance in an obstacle-rich environment [J ] . Journal of Guidance, Control, and Dynamics , 2017 , 40 ( 6 ): 1507 - 1514 . DOI: 10.2514/1.G002355 http://doi.org/10.2514/1.G002355 <空>

YANG M , ZHANG Y N , TAN N , et al . Concise discrete ZNN controllers for end-effector tracking and obstacle avoidance of redundant manipulators [J ] . IEEE Transactions on Industrial Informatics , 2021 , 18 ( 5 ): 3193 - 3202 . DOI: 10.1109/TII.2021.3109426 http://doi.org/10.1109/TII.2021.3109426 https://ieeexplore.ieee.org/document/9529019/ https://ieeexplore.ieee.org/document/9529019/

WANG B , ZHANG Y M , ZHANG W . Integrated path planning and trajectory tracking control for quadrotor UAVs with obstacle avoidance in the presence of environmental and systematic uncertainties: theory and experiment [J ] . Aerospace Science and Technology , 2022 , 120 : 107277 . DOI: 10.1016/j.ast.2021.107277 http://doi.org/10.1016/j.ast.2021.107277 https://linkinghub.elsevier.com/retrieve/pii/S1270963821007872 https://linkinghub.elsevier.com/retrieve/pii/S1270963821007872

LI J , ZHANG J X , ZHANG H H , et al . A predictive guidance obstacle avoidance algorithm for AUV in unknown environments [J ] . Sensors , 2019 , 19 ( 13 ): 2862 . DOI: 10.3390/s19132862 http://doi.org/10.3390/s19132862 https://www.mdpi.com/1424-8220/19/13/2862 https://www.mdpi.com/1424-8220/19/13/2862 A predictive guidance obstacle avoidance algorithm (PGOA) in unknown environments is proposed for autonomous underwater vehicle (AUV) that must adapt to multiple complex obstacle environments. Using the environmental information collected by the Forward-looking Sonar (FLS), the obstacle boundary is simplified by the convex algorithm and Bessel interpolation. Combining the predictive control secondary optimization function and the obstacle avoidance weight function, the predicting obstacle avoidance trajectory parameters are obtained. According to different types of obstacle environments, the corresponding obstacle avoidance rules are formulated. Lastly, combining with the obstacle avoidance parameters and rules, the AUV’s predicting obstacle avoidance trajectory point is obtained. Then AUV can successfully achieve obstacle avoidance using the guidance algorithm. The simulation results show that the PGOA algorithm can better predict the trajectory point of the obstacle avoidance path of AUV, and the secondary optimization function can successfully achieve collision avoidance for different complex obstacle environments. Lastly, comparing the execution efficiency and cost of different algorithms, which deal with various complex obstacle environments, simulation experiment results indicate the high efficiency and great adaptability of the proposed algorithm.

LIN H Y , PENG X Z . Autonomous quadrotor navigation with vision based obstacle avoidance and path planning [J ] . IEEE Access , 2021 , 9 : 102450 - 102459 . DOI: 10.1109/ACCESS.2021.3097945 http://doi.org/10.1109/ACCESS.2021.3097945 https://ieeexplore.ieee.org/document/9490263/ https://ieeexplore.ieee.org/document/9490263/

CHEN H , LU P . Real-time identification and avoidance of simultaneous static and dynamic obstacles on point cloud for UAVs navigation [J ] . Robotics and Autonomous Systems , 2022 , 154 : 104124 . DOI: 10.1016/j.robot.2022.104124 http://doi.org/10.1016/j.robot.2022.104124 https://linkinghub.elsevier.com/retrieve/pii/S0921889022000665 https://linkinghub.elsevier.com/retrieve/pii/S0921889022000665

陈天德 , 黄炎焱 , 沈炜 . 基于虚拟障碍物法的无震荡航路规划 [J ] . 兵工学报 , 2019 , 40 ( 3 ): 651 - 658 . DOI: 10.3969/j.issn.1000-1093.2019.03.025 http://doi.org/10.3969/j.issn.1000-1093.2019.03.025 人工势场法作为路径规划的一种算法，凭借其解算得到的平滑航路，特别适用于不够灵活的移动机器人、智能体的路径规划。由于人工势场法自身不可避免地存在局部极小值以及算法执行不可避免的离散化，导致航路点解算可能会陷入局部极小值陷阱而进入死循环以及出现航路点震荡问题。针对局部极小值陷阱问题，提出改进型虚拟障碍物法；对虚拟障碍物位置的确定，引入了威胁区的概念，并提出了一个确定标准。针对航路点震荡问题，提出过滤震荡点法。仿真实验证明：改进型虚拟障碍物法能够有效地使陷入局部极小值陷阱的航路点解算，成功逃出陷阱；过滤震荡点法能够有效地消除震荡航路点，得到相对平滑的航路。

CHEN T D , HUANG Y Y , SHEN W . Non-oscillation path planning based on virtual obstacle method [J ] . Acta Armamentarii , 2019 , 40 ( 3 ): 651 - 658 . (in Chinese) DOI: 10.3969/j.issn.1000-1093.2019.03.025 http://doi.org/10.3969/j.issn.1000-1093.2019.03.025 The artificial potential field method, as a path planning algorithm, is used for the path planning of clumsy mobile robots, agents and so on because it can provide a smooth route. Due to the inevitable existence of local minimum and discretization of algorithms during algorithm execution, the calculation of the route point may fall into the local minimum trap, which may result in the infinite loop of algorithmic program and the oscillation of path point. For local minimum trap, an improved virtual obstacle method is proposed to overcome this problem. The definition of threat area is introduced to determine the location of virtual obstacle, and a determining standard is put forward. A filtering oscillation point method is proposed to solve the problem of path point oscillation. The simulated results show that the route points which are stuck in local minimum trap can escape from the trap successfully using the improved virtual obstacle method. Additionally, the oscillation route points can be effectively eliminated to obtain a relatively smooth route by the filtering oscillation point method. Key

ZHANG G Q , HAN J , LI J Q , et al . APF-based intelligent navigation approach for USV in presence of mixed potential directions: guidance and control design [J ] . Ocean Engineering , 2022 , 260 : 111972 . DOI: 10.1016/j.oceaneng.2022.111972 http://doi.org/10.1016/j.oceaneng.2022.111972 https://linkinghub.elsevier.com/retrieve/pii/S0029801822013075 https://linkinghub.elsevier.com/retrieve/pii/S0029801822013075

MANCINI M , BLOISE N , CAPELLO E , et al . Sliding mode control techniques and artificial potential field for dynamic collision avoidance in rendezvous maneuvers [J ] . IEEE Control Systems Letters , 2019 , 4 ( 2 ): 313 - 318 . DOI: 10.1109/LCSYS.7782633 http://doi.org/10.1109/LCSYS.7782633 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=7782633 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=7782633

ZHANG N , GAI W D , ZHONG M Y , et al . A fast finite-time convergent guidance law with nonlinear disturbance observer for unmanned aerial vehicles collision avoidance [J ] . Aerospace Science and Technology , 2019 , 86 : 204 - 214 . DOI: 10.1016/j.ast.2019.01.021 http://doi.org/10.1016/j.ast.2019.01.021 https://linkinghub.elsevier.com/retrieve/pii/S1270963818311416 https://linkinghub.elsevier.com/retrieve/pii/S1270963818311416

HE S , SHIN H S , TSOURDOS A . Optimal guidance for integrated waypoint following and obstacle avoidance [C ] //Proceedings of 2019 Workshop on Research, Education and Development of Unmanned Aerial Systems.Cranfield , UK : IEEE , 2019 : 325 - 334 .

KUMAR S R , WEISS M , SHIMA T . Minimum-effort intercept angle guidance with multiple-obstacle avoidance [J ] . Journal of Guidance, Control, and Dynamics , 2018 , 1 ( 6 ): 1355 - 1369 .

XU Y P , LIU L , PENG Z H , et al . Safe motion planning for goal reaching of multiple autonomous surface vehicles based on high-order control barrier functions [C ] //Proceedings of the 2022 IEEE 17th International Conference on Control & Automation. Naples , Italy : IEEE , 2022 : 660 - 664 .

AMES A D , COOGAN S , EGERSTEDT M , et al . Control barrier functions: theory and applications [C ] //Proceedings of the 2019 18th European Control Conference. Napoli , Italy : IEEE , 2019 : 3420 - 3431 .

LIU J Y , ZHAO M , QIAO L . Adaptive barrier lyapunov function-based obstacle avoidance control for an autonomous underwater vehicle with multiple static and moving obstacles [J ] . Ocean Engineering , 2022 , 243 : 110303 . DOI: 10.1016/j.oceaneng.2021.110303 http://doi.org/10.1016/j.oceaneng.2021.110303 https://linkinghub.elsevier.com/retrieve/pii/S0029801821016073 https://linkinghub.elsevier.com/retrieve/pii/S0029801821016073

GARG K , PANAGOU D . Robust control barrier and control lyapunov functions with fixed-time convergence guarantees [C ] //Proceedings of Advances in Computing and Communications. New Orleans, LA , US : IEEE , 2021 : 2292 - 2297 .

LIU Z C , JIANG Z Y , XU T Y , et al . Avoidance of high-speed obstacles based on velocity obstacles [C ] // Proceedings of 2018 IEEE International Conference on Robotics and Automation. Brisbane , Australia : IEEE , 2018 : 7624 - 7630 .

ZHANG M , ZHENG C M , HUANG K . Fixed-wing UAV guidance law for ground target over-flight tracking [J ] . Journal of Systems Engineering and Electronics , 2019 , 30 ( 2 ): 384 - 392 . DOI: 10.21629/JSEE.2019.02.16 http://doi.org/10.21629/JSEE.2019.02.16 This paper studies the problem of tracking a ground target for a fixed-wing unmanned aerial vehicle (UAV) based on the proposed guidance law. The algorithm ensures that a UAV continuously overflies the target whether it is fixed or moving. The requirements of the UAV flight constraints such as bounded air-speed and acceleration are considered. A Lyapunov function is constructed to prove the stability of the proposed guidance law, and parameter design criteria have been developed. Considering the fixed and moving ground targets, numerical simulations are performed to verify the feasibility and benefits of the proposed guidance algorithm.

QU Y , YI W J . Three-dimensional obstacle avoidance strategy for fixed-wing UAVs based on quaternion method [J ] . Applied Sciences , 2022 , 12 ( 3 ): 955 . DOI: 10.3390/app12030955 http://doi.org/10.3390/app12030955 https://www.mdpi.com/2076-3417/12/3/955 https://www.mdpi.com/2076-3417/12/3/955 This work provides a generalization of the three-dimensional velocity obstacle (VO) collision avoidance strategy for nonlinear second-order underactuated systems in three-dimensional dynamic uncertain environments. A hierarchical architecture is exploited to deal with conflicting multiple subtasks, which are defined as several rotations and are parameterized by quaternions. An improved VO method considering the kinodynamic constraints of a class of fixed-wing unmanned aerial vehicles (UAV) is proposed to implement the motion planning. The position error and velocity error can be mapped onto one desired axis so that, only relying on an engine, UAVs can achieve the goal of point tracking without collision. Additionally, the performance of the closed-loop system is demonstrated through a series of simulations performed in a three-dimensional manner.

GUO K , WANG D W , FAN T X , et al . VR-ORCA: variable responsibility optimal reciprocal collision avoidance [J ] . IEEE Robotics and Automation Letters , 2021 , 6 ( 3 ): 4520 - 4527 . DOI: 10.1109/LRA.2021.3067851 http://doi.org/10.1109/LRA.2021.3067851 https://ieeexplore.ieee.org/document/9384148/ https://ieeexplore.ieee.org/document/9384148/

PARK J , CHO N , LEE S . Reactive collision avoidance algorithm for UAV using bounding tube against multiple moving obstacles [J ] . IEEE Access , 2020 , 8 : 218131 - 218144 . DOI: 10.1109/Access.6287639 http://doi.org/10.1109/Access.6287639 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639

XIAO F , ZHENG P , TRIA J D , et al . Optic flow-based reactive collision prevention for MAVs using the fictitious obstacle hypothesis [J ] . IEEE Robotics and Automation Letters , 2021 , 6 ( 2 ): 3144 - 3151 . DOI: 10.1109/LSP.2016. http://doi.org/10.1109/LSP.2016. https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=7083369 https://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=7083369

SHIN H S , LI K B . An improvement in three-dimensional pure proportional navigation guidance [J ] . IEEE Transactions on Aerospace and Electronic Systems , 2021 , 57 ( 5 ): 3004 - 3014 . DOI: 10.1109/TAES.2021.3067656 http://doi.org/10.1109/TAES.2021.3067656 https://ieeexplore.ieee.org/document/9384239/ https://ieeexplore.ieee.org/document/9384239/

WANG Y N , WANG H , LIN D F , et al . Nonlinear modified bias proportional navigation guidance law against maneuvering targets [J ] . Journal of the Franklin Institute , 2022 , 359 ( 7 ): 2949 - 2975 . DOI: 10.1016/j.jfranklin.2022.02.012 http://doi.org/10.1016/j.jfranklin.2022.02.012 https://linkinghub.elsevier.com/retrieve/pii/S0016003222001120 https://linkinghub.elsevier.com/retrieve/pii/S0016003222001120

QI Q M , LI C W , ZHANG Z L , et al . Parallel test of optical automatic target recognition system for loitering munition based on digital twin [C ] //Proceedings of 2021 International Conference on Control, Automation and Information Sciences. Xi'an , China : IEEE , 2021 : 955 - 961 .