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16 pages, 4628 KiB

Open AccessArticle

Evaluation and Selection of Video Stabilization Techniques for UAV-Based Active Infrared Thermography Application

by Shashank Pant, Parham Nooralishahi, Nicolas P. Avdelidis, Clemente Ibarra-Castanedo, Marc Genest, Shakeb Deane, Julio J. Valdes, Argyrios Zolotas and Xavier P. V. Maldague

Sensors 2021, 21(5), 1604; https://doi.org/10.3390/s21051604 - 25 Feb 2021

Cited by 9 | Viewed by 4382

Abstract

Unmanned Aerial Vehicles (UAVs) that can fly around an aircraft carrying several sensors, e.g., thermal and optical cameras, to inspect the parts of interest without removing them can have significant impact in reducing inspection time and cost. One of the main challenges in [...] Read more.

Unmanned Aerial Vehicles (UAVs) that can fly around an aircraft carrying several sensors, e.g., thermal and optical cameras, to inspect the parts of interest without removing them can have significant impact in reducing inspection time and cost. One of the main challenges in the UAV based active InfraRed Thermography (IRT) inspection is the UAV’s unexpected motions. Since active thermography is mainly concerned with the analysis of thermal sequences, unexpected motions can disturb the thermal profiling and cause data misinterpretation especially for providing an automated process pipeline of such inspections. Additionally, in the scenarios where post-analysis is intended to be applied by an inspector, the UAV’s unexpected motions can increase the risk of human error, data misinterpretation, and incorrect characterization of possible defects. Therefore, post-processing is required to minimize/eliminate such undesired motions using digital video stabilization techniques. There are number of video stabilization algorithms that are readily available; however, selecting the best suited one is also challenging. Therefore, this paper evaluates video stabilization algorithms to minimize/mitigate undesired UAV motion and proposes a simple method to find the best suited stabilization algorithm as a fundamental first step towards a fully operational UAV-IRT inspection system. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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27 pages, 38837 KiB

Open AccessArticle

A UAV-Based Eddy Covariance System for Measurement of Mass and Energy Exchange of the Ecosystem: Preliminary Results

by Yibo Sun, Junyong Ma, Bilige Sude, Xingwen Lin, Haolu Shang, Bing Geng, Zhaoyan Diao, Jiaqiang Du and Zhanjun Quan

Sensors 2021, 21(2), 403; https://doi.org/10.3390/s21020403 - 8 Jan 2021

Cited by 8 | Viewed by 4659

Abstract

Airborne eddy covariance (EC) measurement is one of the most effective methods to directly measure the surface mass and energy fluxes at the regional scale. It offers the possibility to bridge the scale gap between local- and global-scale measurements by ground-based sites and [...] Read more.

Airborne eddy covariance (EC) measurement is one of the most effective methods to directly measure the surface mass and energy fluxes at the regional scale. It offers the possibility to bridge the scale gap between local- and global-scale measurements by ground-based sites and remote-sensing instrumentations, and to validate the surface fluxes estimated by satellite products or process-based models. In this study, we developed an unmanned aerial vehicle (UAV)-based EC system that can be operated to measure the turbulent fluxes in carbon dioxides, momentum, latent and sensible heat, as well as net radiation and photosynthetically active radiation. Flight tests of the developed UAV-based EC system over land were conducted in October 2020 in Inner Mongolia, China. The in-flight calibration was firstly conducted to correct the mounting error. Then, three flight comparison tests were performed, and we compared the measurement with those from a ground tower. The results, along with power spectral comparison and consideration of the differing measurement strategies indicate that the system can resolve the turbulent fluxes in the encountered measurement condition. Lastly, the challenges of the UAV-based EC method were discussed, and potential improvements with further development were explored. The results of this paper reveal the considerable potential of the UAV-based EC method for land surface process studies. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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24 pages, 12172 KiB

Open AccessArticle

Development of Non Expensive Technologies for Precise Maneuvering of Completely Autonomous Unmanned Aerial Vehicles

by Luca Bigazzi, Stefano Gherardini, Giacomo Innocenti and Michele Basso

Sensors 2021, 21(2), 391; https://doi.org/10.3390/s21020391 - 8 Jan 2021

Cited by 11 | Viewed by 3468

Abstract

In this paper, solutions for precise maneuvering of an autonomous small (e.g., 350-class) Unmanned Aerial Vehicles (UAVs) are designed and implemented from smart modifications of non expensive mass market technologies. The considered class of vehicles suffers from light load, and, therefore, only a [...] Read more.

In this paper, solutions for precise maneuvering of an autonomous small (e.g., 350-class) Unmanned Aerial Vehicles (UAVs) are designed and implemented from smart modifications of non expensive mass market technologies. The considered class of vehicles suffers from light load, and, therefore, only a limited amount of sensors and computing devices can be installed on-board. Then, to make the prototype capable of moving autonomously along a fixed trajectory, a “cyber-pilot”, able on demand to replace the human operator, has been implemented on an embedded control board. This cyber-pilot overrides the commands thanks to a custom hardware signal mixer. The drone is able to localize itself in the environment without ground assistance by using a camera possibly mounted on a 3 Degrees Of Freedom (DOF) gimbal suspension. A computer vision system elaborates the video stream pointing out land markers with known absolute position and orientation. This information is fused with accelerations from a 6-DOF Inertial Measurement Unit (IMU) to generate a “virtual sensor” which provides refined estimates of the pose, the absolute position, the speed and the angular velocities of the drone. Due to the importance of this sensor, several fusion strategies have been investigated. The resulting data are, finally, fed to a control algorithm featuring a number of uncoupled digital PID controllers which work to bring to zero the displacement from the desired trajectory. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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11 pages, 1518 KiB

Open AccessArticle

Application of a Small Unmanned Aerial System to Measure Ammonia Emissions from a Pilot Amine-CO₂ Capture System

by Travis J. Schuyler, Bradley Irvin, Keemia Abad, Jesse G. Thompson, Kunlei Liu and Marcelo I. Guzman

Sensors 2020, 20(23), 6974; https://doi.org/10.3390/s20236974 - 6 Dec 2020

Cited by 1 | Viewed by 4955

Abstract

The quantification of atmospheric gases with small unmanned aerial systems (sUAS) is expanding the ability to safely perform environmental monitoring tasks and quickly evaluate the impact of technologies. In this work, a calibrated sUAS is used to quantify the emissions of ammonia (NH [...] Read more.

The quantification of atmospheric gases with small unmanned aerial systems (sUAS) is expanding the ability to safely perform environmental monitoring tasks and quickly evaluate the impact of technologies. In this work, a calibrated sUAS is used to quantify the emissions of ammonia (NH₃) gas from the exit stack a 0.1 MWth pilot-scale carbon capture system (CCS) employing a 5 M monoethanolamine (MEA) solvent to scrub CO₂ from coal combustion flue gas. A comparison of the results using the sUAS against the ion chromatography technique with the EPA CTM-027 method for the standard emission sampling of NH₃ shows good agreement. Therefore, the work demonstrates the usefulness of sUAS as an alternative method of emission measurement, supporting its application in lieu of traditional sampling techniques to collect real time emission data. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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16 pages, 4446 KiB

Open AccessEditor’s ChoiceArticle

Optimal Frontier-Based Autonomous Exploration in Unconstructed Environment Using RGB-D Sensor

by Liang Lu, Carlos Redondo and Pascual Campoy

Sensors 2020, 20(22), 6507; https://doi.org/10.3390/s20226507 - 14 Nov 2020

Cited by 30 | Viewed by 4826

Abstract

Aerial robots are widely used in search and rescue applications because of their small size and high maneuvering. However, designing an autonomous exploration algorithm is still a challenging and open task, because of the limited payload and computing resources on board UAVs. This [...] Read more.

Aerial robots are widely used in search and rescue applications because of their small size and high maneuvering. However, designing an autonomous exploration algorithm is still a challenging and open task, because of the limited payload and computing resources on board UAVs. This paper presents an autonomous exploration algorithm for the aerial robots that shows several improvements for being used in the search and rescue tasks. First of all, an RGB-D sensor is used to receive information from the environment and the OctoMap divides the environment into obstacles, free and unknown spaces. Then, a clustering algorithm is used to filter the frontiers extracted from the OctoMap, and an information gain based cost function is applied to choose the optimal frontier. At last, the feasible path is given by A* path planner and a safe corridor generation algorithm. The proposed algorithm has been tested and compared with baseline algorithms in three different environments with the map resolutions of

0.2

m, and

0.3

m. The experimental results show that the proposed algorithm has a shorter exploration path and can save more exploration time when compared with the state of the art. The algorithm has also been validated in the real flight experiments. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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15 pages, 4836 KiB

Open AccessArticle

The Effect of a Flow Field on Chemical Detection Performance of Quadrotor Drone

by Sangwon Do, Myeongjae Lee and Jong-Seon Kim

Sensors 2020, 20(11), 3262; https://doi.org/10.3390/s20113262 - 8 Jun 2020

Cited by 19 | Viewed by 4281

Abstract

The determination of a suitable sensor location on quadrotor drones is a very important issue for chemical reconnaissance platforms because the magnitude and direction of air velocity is different for each location. In this study, we investigated a customized chemical reconnaissance system consisting [...] Read more.

The determination of a suitable sensor location on quadrotor drones is a very important issue for chemical reconnaissance platforms because the magnitude and direction of air velocity is different for each location. In this study, we investigated a customized chemical reconnaissance system consisting of a quadrotor drone and a chip-sized chemical sensor for detecting dimethyl-methylphosphonate (DMMP; a Sarin simulant) and investigated the chemical detection properties with respect to the sensor position through indoor experiments and particle image velocimetry (PIV) analysis of the system. The PIV results revealed an area free of vortex–vortex interaction between the drone rotors, where there was distinctly stable and uniform chemical detection of DMMP. The proposed chemical reconnaissance system was found to be realistic for practical application. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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15 pages, 8618 KiB

Open AccessArticle

High-Altitude Balloon-Based Sensor System Design and Implementation

by Zhanchao Wang, Min Huang, Lulu Qian, Baowei Zhao and Guangming Wang

Sensors 2020, 20(7), 2080; https://doi.org/10.3390/s20072080 - 7 Apr 2020

Cited by 9 | Viewed by 26462

Abstract

As a kind of large-scale unmanned aerial vehicle, a high-altitude balloon can carry a large load up to tens of kilometers in the near space for a long time, which brings a new way for the stratosphere atmospheric detection. In order to provide [...] Read more.

As a kind of large-scale unmanned aerial vehicle, a high-altitude balloon can carry a large load up to tens of kilometers in the near space for a long time, which brings a new way for the stratosphere atmospheric detection. In order to provide a suitable working environment for the near-space detection load, it is necessary to design a sensor system based on a high-altitude balloon, which is used to provide environmental temperature, height position, and attitude information, current working, and video surveillance. The high-altitude balloon-based sensor system designed in this paper had participated in the near-space flight experiment, whose total flight time was 30 h and 53 min, and the horizontal flight time was 28 h and 58 min crossing the day and night. The high-altitude balloon-based sensor system had withstood the severe environment of the near-space during the day and night, providing accurate temperature measurement, real-time altitude position and attitude data acquisition, reliable current monitoring, and comprehensive video surveillance. In the next three years, the high-altitude balloon-based sensor system developed in this paper will continue to participate in the experiment and provide support for more detection loads. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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16 pages, 7941 KiB

Open AccessArticle

Feasibility of Discriminating UAV Propellers Noise from Distress Signals to Locate People in Enclosed Environments Using MEMS Microphone Arrays

by Alberto Izquierdo, Lara del Val, Juan J. Villacorta, Weikun Zhen, Sebastian Scherer and Zheng Fang

Sensors 2020, 20(3), 597; https://doi.org/10.3390/s20030597 - 21 Jan 2020

Cited by 8 | Viewed by 3556

Abstract

Detecting and finding people are complex tasks when visibility is reduced. This happens, for example, if a fire occurs. In these situations, heat sources and large amounts of smoke are generated. Under these circumstances, locating survivors using thermal or conventional cameras is not [...] Read more.

Detecting and finding people are complex tasks when visibility is reduced. This happens, for example, if a fire occurs. In these situations, heat sources and large amounts of smoke are generated. Under these circumstances, locating survivors using thermal or conventional cameras is not possible and it is necessary to use alternative techniques. The challenge of this work was to analyze if it is feasible the integration of an acoustic camera, developed at the University of Valladolid, on an unmanned aerial vehicle (UAV) to locate, by sound, people who are calling for help, in enclosed environments with reduced visibility. The acoustic array, based on MEMS (micro-electro-mechanical system) microphones, locates acoustic sources in space, and the UAV navigates autonomously by closed enclosures. This paper presents the first experimental results locating the angles of arrival of multiple sound sources, including the cries for help of a person, in an enclosed environment. The results are promising, as the system proves able to discriminate the noise generated by the propellers of the UAV, at the same time it identifies the angles of arrival of the direct sound signal and its first echoes reflected on the reflective surfaces. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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11 pages, 2655 KiB

Open AccessArticle

Cavity Ring-Down Methane Sensor for Small Unmanned Aerial Systems

by Benjamin Martinez, Thomas W. Miller and Azer P. Yalin

Sensors 2020, 20(2), 454; https://doi.org/10.3390/s20020454 - 14 Jan 2020

Cited by 34 | Viewed by 5955

Abstract

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 [...] Read more.

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of ~10–30 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate point-source methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as ~0.005 g/s can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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16 pages, 4445 KiB

Open AccessArticle

Engineering Design of an Active–Passive Combined Thermal Control Technology for an Aerial Optoelectronic Platform

by Zhifeng Cheng, Lu Sun, Fuhe Liu, Xiaofeng Liu, Lei Li, Quanchao Li and Richa Hu

Sensors 2019, 19(23), 5241; https://doi.org/10.3390/s19235241 - 28 Nov 2019

Cited by 10 | Viewed by 2582

Abstract

In order to ensure the imaging performance of the aerial optoelectronic platform system in low temperature environment, an active-passive combined thermal control technology was studied. A thermal control finite element model of the aerial optoelectronic platform was established. Additionally, thermal control simulation analysis [...] Read more.

In order to ensure the imaging performance of the aerial optoelectronic platform system in low temperature environment, an active-passive combined thermal control technology was studied. A thermal control finite element model of the aerial optoelectronic platform was established. Additionally, thermal control simulation analysis and experiments under extreme conditions were carried out respectively. The simulation and experimental results showed that the temperature level of the primary mirror is improved above 25 °C by the proposed thermal control technology effectively, meanwhile the temperature gradient of the primary and secondary mirrors are less than 5 °C. The successful implementation of this active-passive combined thermal control technology provides a technical support for the precision thermal control of aerial optoelectronic platforms. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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17 pages, 3623 KiB

Open AccessArticle

Rigorous Calibration of UAV-Based LiDAR Systems with Refinement of the Boresight Angles Using a Point-to-Plane Approach

by Elizeu Martins de Oliveira Junior and Daniel Rodrigues dos Santos

Sensors 2019, 19(23), 5224; https://doi.org/10.3390/s19235224 - 28 Nov 2019

Cited by 13 | Viewed by 3391

Abstract

Advances in micro-electro-mechanical navigation systems and lightweight LIDAR (light detection and ranging) sensors onboard unmanned aerial vehicles (UAVs) provide the feasibility of deriving point clouds with very high and homogeneous point density. However, the deformations caused by numerous sources of errors should be [...] Read more.

Advances in micro-electro-mechanical navigation systems and lightweight LIDAR (light detection and ranging) sensors onboard unmanned aerial vehicles (UAVs) provide the feasibility of deriving point clouds with very high and homogeneous point density. However, the deformations caused by numerous sources of errors should be carefully treated. This work presents a rigorous calibration of UAV-based LiDAR systems with refinement of the boresight angles using a point-to-plane approach. Our method is divided into a calibration and a parameter mounting refinement part. It starts with the estimation of the calibration parameters and then refines the boresight angles. The novel contribution of the paper is two-fold. First, we estimate the calibration parameters conditioning the centroid of a plane segmented to lie on its corresponding segmented plane without an additional surveying campaign. Second, we refine the boresight angles using a new point-to-plane model. The proposed method is evaluated by analyzing the accuracy assessment of the adjusted point cloud to point/planar features before and after the proposed method. Compared with the state-of-the-art method, our proposed method achieves better positional accuracy. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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20 pages, 8315 KiB

Open AccessArticle

A Survey of Practical Design Considerations of Optical Imaging Stabilization Systems for Small Unmanned Aerial Systems

by Christopher Dahlin Rodin, Fabio Augusto de Alcantara Andrade, Anthony Reinier Hovenburg and Tor Arne Johansen

Sensors 2019, 19(21), 4800; https://doi.org/10.3390/s19214800 - 4 Nov 2019

Cited by 13 | Viewed by 5124

Abstract

Optical imaging systems are one of the most common sensors used for collecting data with small Unmanned Aerial Systems (sUAS). Plenty of research exists which present custom-made optical imaging systems for specific missions. However, the research commonly leaves out the explanation of design [...] Read more.

Optical imaging systems are one of the most common sensors used for collecting data with small Unmanned Aerial Systems (sUAS). Plenty of research exists which present custom-made optical imaging systems for specific missions. However, the research commonly leaves out the explanation of design parameters and considerations taken during the design of the optical imaging system, especially the image stabilization strategy used, which is a significant issue in sUAS imaging missions. This paper surveys useful methodologies for designing a stabilized optical imaging system by presenting an overview of the important aspects that must be addressed in the designing phase and which tools and techniques are available and should be chosen according to the design requirements. Full article

(This article belongs to the Special Issue Sensors for Unmanned Aircraft Systems and Related Technologies)

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