Electro-optical Sensors Research Articles

Infra-red line camera data-driven edge detector in UAV forest fire monitoring

The accurate prediction of the wildfire spread-rate is a challenging task, due to the high number of parameters involved and the underlying complex dynamic multi-physics processes which drive the phenomenon. For these reasons, data-driven prediction tools could be useful to provide a more accurate prediction of the fire front. In this scenario, systematic fire data gathering becomes crucial and using an Unmanned Aircraft Vehicle (UAV) is strategic to reduce considerably the risk associated with flying a manned aircraft into low visibility and extremely turbulent air, sustained by the fire-induced convective motions.Moreover the employment of the UAV is beneficial, as the possibility of flying at very low altitudes maximizes the on-board Electro-Optical (EO) sensor effectiveness. The aim is to develop a real time data-driven fire propagator to support wildfire fighting operations and to facilitate the risk assessment and decision making process. In order to collect data, the fire front position has to be measured using an infra-red (IR) camera so as to overcome the limitations associated to a visible camera in low visibility (smoky)conditions and night operations. To reduce the computational cost associated to the image processing, a Line Camera (LC) configuration has been preferred. Because of the mono-dimensionality of the measure, classical edge detector, like the Canny method, or contour algorithms, developed for 2D images, can not be applied. In this paper, a mono-dimensional noise-resistant algorithm for edge detection is presented. The generality of the proposed method opens the possibility to a variety of heterogeneous problems of different nature. The robustness of this algorithm resides in the use of known physical characteristics of the target of interest, to increase the feature edge discontinuity. Its straightforwardness guarantees fast computation, making it very attractive for real time image processing, remote sensing applications and for UAV surveillance tasks.

Fabrication of micro-optical connectors for electro-optical sensor devices by a combined femtosecond laser system

The article demonstrates the fundamental possibility of creating microstructures for various functional purposes using the capabilities of the two-photon femtosecond polymerization method. The developed technological approach for creating a micro-optical holder for standard single-mode and multimode fibers is demonstrated. This type of holder can be used to manufacture a unit for optical matching of optical fibers with sensitive optical elements. The possibility of optical matching of fibers with a superconducting single-photon detector, an array system of bolometric superconducting microbridges, and spherical self-formed microlenses by near infrared-sensitive photopolymerization has been experimentally shown. The device manufacturing process was carried out in a combined single laser micromachining facility using femtosecond laser radiation for lithography with submicron resolution, texturing of the sensor surface, and the formation of microstructures for installing single-mode optical fibers.

ASAS-NANP SYMPOSIUM: Applications of machine learning for livestock body weight prediction from digital images.

Monitoring, recording, and predicting livestock body weight (BW) allows for timely intervention in diets and health, greater efficiency in genetic selection, and identification of optimal times to market animals because animals that have already reached the point of slaughter represent a burden for the feedlot. There are currently two main approaches (direct and indirect) to measure the BW in livestock. Direct approaches include partial-weight or full-weight industrial scales placed in designated locations on large farms that measure passively or dynamically the weight of livestock. While these devices are very accurate, their acquisition, intended purpose and operation size, repeated calibration and maintenance costs associated with their placement in high-temperature variability, and corrosive environments are significant and beyond the affordability and sustainability limits of small and medium size farms and even of commercial operators. As a more affordable alternative to direct weighing approaches, indirect approaches have been developed based on observed or inferred relationships between biometric and morphometric measurements of livestock and their BW. Initial indirect approaches involved manual measurements of animals using measuring tapes and tubes and the use of regression equations able to correlate such measurements with BW. While such approaches have good BW prediction accuracies, they are time consuming, require trained and skilled farm laborers, and can be stressful for both animals and handlers especially when repeated daily. With the concomitant advancement of contactless electro-optical sensors (e.g., 2D, 3D, infrared cameras), computer vision (CV) technologies, and artificial intelligence fields such as machine learning (ML) and deep learning (DL), 2D and 3D images have started to be used as biometric and morphometric proxies for BW estimations. This manuscript provides a review of CV-based and ML/DL-based BW prediction methods and discusses their strengths, weaknesses, and industry applicability potential.

Core–Shell Gold Nanoparticle-Star Copolymer Composites with Gradient Transfer and Transport Properties: Toward Electro-Optical Sensors and Catalysis

A series of hybrid core–shell nanomaterials was prepared by solvent phase transfer methods with gold (Au) nanoparticles (NPs) as a core and star copolymers (h-PEI-b-PCL-Cbz) as a shell—consisting o...

Design study of a compact ultra-wide-angle high-spatial-resolution high-spectral-resolution snapshot imaging spectrometer

An ultra-wide-angle high-spatial-resolution high-spectral-resolution snapshot imaging spectrometer (UWA-2HSR-SIS) is presented, which comprises a microlens array (MLA), multiple fiber bundles, a micro-cylindrical-lens array (MCLA), a cylindrical lens, a static grating interferometer (SGI), and an area-array detector. The MLA is arranged in a circular arc of 120° or more. The MCLA is arranged in a straight line. The SGI includes a fixed reflection grating in Littrow configuration, a beam splitter, and a fixed plane mirror. Each fiber bundle containing multiple optical fibers is coupled to a separate microlens of the MLA, subdividing the field angle of each microlens into multiple smaller field angles. The light passing through each subdivided smaller field angle of each microlens of the MLA is received by a separate part of the detector. The UWA-2HSR-SIS is a new concept that not only obtains both high spatial resolution and high spectral resolution based on a single sensor for the first time, but also has an ultra-wide field angle in the horizontal plane, can obtain spectral information covering the full spectral range of interest in real time, and is very stable against various disturbances. The UWA-2HSR-SIS has great potential for remote sensing electro-optical reconnaissance sensors in the visible and near-infrared region.

Surface modification and properties modulation of rGO film by short duration H2 and NH3 plasma treatment

Reduced graphene oxide (rGO) is a versatile material due to the presence of oxygen functionalization. One of the methods to tune the properties of rGO for the specific application is plasma treatment. Plasma H 2 and NH 3 are known introduced surface defects for increasing surface reactivity and inducing substitutional doping on rGO film. They need to be further discussed with the changes in electrical and optical properties of the film for the construction of devices such as electrical, optical, and electro-optical sensors. This article reports the effect of H 2 and NH 3 plasma treatment on the surface and properties of rGO film using a variety in plasma power and temperature. We found low-power H 2 plasma at low- and medium-temperature induced further de-oxygenation of rGO. A tiny etching effect by H 2 plasma slightly reduces the conductivity, σ to 54.01 S/cm from the reference rGO value of 448.90 S/cm. Low-power H 2 plasma at high-temperature left the high defective sites due to plasma etching. The σ was reduced to 8.04 S/cm. Medium-temperature medium-power NH 3 plasma did not effective for N-doping. An etching effect by NH 3 plasma noticeably reduces the σ to 5.79 S/cm. Medium-temperature high-power and high-temperature medium-power NH 3 plasma induce N-doping but at the same time significantly etch the rGO. They significantly reduce the hole concentration and lower the σ to 0.48 S/cm. High-power high-temperature NH 3 plasma rigorously induces N-doping but extreme plasma etching results in poor surface condition and film discontinuity. The film exhibited electron as a majority carrier but with the lowest σ of 0.05 S/cm.

Object Detection at Sea Using Ensemble Methods Across Spectral Ranges

Abstract Having the option of a temporally unmanned bridge when conditions allow, while maintaining or even enhancing navigational safety, is a long term aim in the maritime industry. Such a system requires excellent perception of the environment using an array of sensors. This paper investigates performance of object detection at sea using electro-optical sensors in relevant spectral ranges and discusses how missed detection risk is minimised for objects within navigation range. Using a combination of cameras in visible, near- and far infrared ranges, convolutional neural networks are employed for object detection. Ensemble techniques are suggested to minimise the amount of missed detections and it is shown how optimisation of confidence thresholds can be used to increase performance. The results are based on image data from vessels in near-coast operation in Danish waters.

A Transfer Function Measurement Setup With an Electro-Optic Sensor for MR Safety Assessment in Cascaded Media

This article introduces a transfer function (TF) measurement setup for cascaded media (CM) and demonstrates that the full immersion of an implant in a lossy medium might result in an underestimation of the RF-induced heating compared to partial immersion. A CMTF measurement setup was constructed using medium-specific local electric field sources and electro-optical sensor (EOS). TFs of bare and insulated wire samples were measured in the CM air/saline. Finite-difference time-domain (FDTD) simulations were implemented using a reciprocal approach with a monopole excitation source as well as a piecewise plane wave excitation method. As a theoretical guideline for understanding the CM behavior of the devices, an analytical model based on the buried wire models was derived. CMTFs agree with good precision between FDTD simulations, analytical modeling, and the EOS measurements. Measured TFs were calibrated and validated similar to ISO/TS 10974:Ed.2. Calculated tip SAR values under uniform incident field show an increase up to a factor of 5.7 for partially immersed wires compared to the full immersion. On average, FDTD-based TFs overestimate SAR by 25% compared to measurement-based TFs. As safety assessments for fully immersed implant leads or devices might not represent the worst-case scenario, single-medium assessments might underestimate the RF-induced heating.

Sensitivity Characteristics of Electro-Optical Sensors Under AC/DC Hybrid Electric Fields in Oil Medium Environment

The measurement of ac/dc hybrid electric fields in converter transformers is important for the verification of electric field calculation model and the insulation optimization. Electro-optical (EO) sensors have obvious advantages for measuring strong electric fields, but their response characteristics and mechanisms under the action of ac/dc hybrid electric fields are not fully understood by researchers, which restricts a wide application of sensors. In this article, we first describe an improved dual-beam structure, which enables us to measure both ac and dc electric fields in oil simultaneously. Next, the complete output characteristics of the EO sensor under ac/dc hybrid electric field are obtained through experiments. The results show that measurement sensitivities of EO sensor under dc and ac electric fields are different; there is a coupling effect in measuring ac/dc hybrid electric fields: the increase of one electric field component will reduce the sensor's measurement sensitivity to the other electric field component, which is more obvious for a strong electric field. Finally, we propose the response mechanism with theoretical analysis. First, the sensitivity difference is due to the difference of electric fields inside EO crystal under ac and dc electric fields, and it is affected by the conductivity and dielectric constant of crystal and oil medium. Second, the optical nonlinearity of EO sensors under strong electric fields is the cause of coupling effect: the sensor's nonlinear modulation of a strong ac electric field will introduce coupling errors in measurement signal of the dc electric field and a strong dc electric field will move the zero point of the sensor's ac induction curve from the linear region to the nonlinear region, causing the ac sensitivity to decrease nonlinearly with the increase of the applied dc electric field. This article provides a measurement and analysis of EO sensors under ac/dc hybrid electric fields in an oil medium environment, which is beneficial to the wide application of EO sensors.

Target tracking algorithms for multi-UAVs formation cooperative detection*

This paper considers the problem of the ground target positioning and tracking algorithm for multi UAVs formation cooperative detection, and a real time and fast algorithm is proposed based on UAV airborne electro optical sensors. One state estimation problem for nonlinear stochastic system is studied by means of the unscented Kalman filter algorithm from target tracking process. To extend the single target tracking to multiple target tracking, one improved unscented Kalman filter algorithm is advised based on iterative multiple models. Furthermore, to relax the strict condition on white noise in Kalman filtering, the target tracking or state estimation is reduced to derive the inner and outer ellipsoidal approximations for the state in case of unknown but bounded noise. Finally, one simulation example confirms our theoretical results.

Optimization of dielectric films with dual ion beam sputtering deposition for high reflectivity mirrors

Abstract Dielectric thin films deposited by Ion beam sputtering deposition technique have superior properties of good adhesion and customized optical properties suits to many optical filters for electro-optical sensors. In the present work Tantalum Pentoxide (Tantala) and Silicon Dioxide (Silica) thin films are fabricated with dual ion beam sputtering deposition process. The process parameters are optimized to achieve better surface quality and optical constants. The effect of the assist ion beam on the film properties is evaluated. Multi-layer dielectric mirrors realized with 1000 ppm loss on optimization of single-layer Silica and Tantala films, which will be suitable for linear and Ring Laser Resonators. The films are characterized by ellipsometer, non-contact optical profiler, spectrophotometer, and cavity ring-down loss meter. The multi-layer mirrors were subjected to vacuum annealing and the effect of annealing on film reflectivity is evaluated. The work emphasizes the process requirements of Ion Beam Sputtering to realize high reflectivity and low loss mirrors of Tantala and Silica films from Ta2O5 and SiO2 target materials. It gives an insight into the process deficiencies in matching the theoretical design of multi-layer mirrors from the practical aspects of coatings.

An unprecedented spike of the electroluminescence turn-on transience from guest-doped OLEDs with strong electron-donating abilities of host carbazole groups.

An unreported unprecedented spike of ∼μs line-width, followed by an overshoot, was discovered at the rising edge of transient electroluminescence (TEL) from guest-doped organic light-emitting diodes with strong electron-donating abilities from the host carbazole groups. By changing the device structures and TEL measurement parameters, a series of experimental results demonstrate that this TEL spike is not related to exciton interactions such as singlet-triplet and triplet-triplet annihilations but originated from the radiative recombination of pre-stored electrons with injected holes. Surprisingly, these pre-stored guest electrons do not come from the energy-level traps in the host-guest systems; instead, the guest molecules receive the electrons transferred from the host carbazole groups due to their strong electron-donating abilities. Moreover, the observed spikes show rich and extraordinary temperature dependences. Based on the detailed understanding of the spike formation mechanism, we have proposed the requirements for the occurrence of spike and realized the artificial adjustments of the spike intensity. For instance, the instantaneous luminescent intensity of this spike can reach over 80 times the magnitude of the TEL plateau. Accordingly, this work deepens the physical understanding of this novel spike in TEL and paves the way for fabricating an electro-optic sensor to detect instantaneous weak current signals.

Open Water Detection for Autonomous In-harbor Navigation Using a Classification Network

Autonomous navigation quay to quay is a goal for various surface vessel trades, from inland ferries to river transport and offshore services. Ability to navigate safely within a harbour or other confined waters is an essential step-stone towards this goal. This paper aims at creating a map of open water area that is available for safe navigation, given dynamic and static obstacles. Employing electro-optical sensors, the paper suggests open water detection using a classification convolutional neural network on context sensitive sub-partitioning of an image in a pyramid of smaller areas, combining the classifications in to a map of subareas containing open water. A salient feature of this approach is the ease of annotation and ease of creating a large amount of annotated images that is needed for machine learning. Following classification of sub-areas, camera images are transformed to bird’s view by projective geometry methods to enable planning of feasible paths for navigation. This new approach is validated on data from sea trials in Danish waters.

Active and Passive Electro-Optical Sensors for Health Assessment in Food Crops.

In agriculture, early detection of plant stresses is advantageous in preventing crop yield losses. Remote sensors are increasingly being utilized for crop health monitoring, offering non-destructive, spatialized detection and the quantification of plant diseases at various levels of measurement. Advances in sensor technologies have promoted the development of novel techniques for precision agriculture. As in situ techniques are surpassed by multispectral imaging, refinement of hyperspectral imaging and the promising emergence of light detection and ranging (LIDAR), remote sensing will define the future of biotic and abiotic plant stress detection, crop yield estimation and product quality. The added value of LIDAR-based systems stems from their greater flexibility in capturing data, high rate of data delivery and suitability for a high level of automation while overcoming the shortcomings of passive systems limited by atmospheric conditions, changes in light, viewing angle and canopy structure. In particular, a multi-sensor systems approach and associated data fusion techniques (i.e., blending LIDAR with existing electro-optical sensors) offer increased accuracy in plant disease detection by focusing on traditional optimal estimation and the adoption of artificial intelligence techniques for spatially and temporally distributed big data. When applied across different platforms (handheld, ground-based, airborne, ground/aerial robotic vehicles or satellites), these electro-optical sensors offer new avenues to predict and react to plant stress and disease. This review examines the key sensor characteristics, platform integration options and data analysis techniques recently proposed in the field of precision agriculture and highlights the key challenges and benefits of each concept towards informing future research in this very important and rapidly growing field.

Bacteria-based electro-optical platform for ampicillin detection in aquatic solutions

We have shown for the first time that it is possible to use a bacteria-based sensory system consisting of the bacterium Pseudomonas putida TSh-18 and an electro-optical sensor to detect ampicillin in the concentration range 0.5–600 μg/mL. Changes in the anisotropy of cell polarizability were detected at 900 and 2100 kHz; these represented the state of the cytoplasm and of the cell membrane, respectively. The changes indicate the quickest cell response to changes in the characteristics of the bacterial culture exposed to ampicillin. We have also shown that it is possible to monitor the ampicillin in the presence of kanamycin. In control experiments, we examined the effects of ampicillin and kanamycin on bacterial cells by phase-contrast microscopy and by standard microbiological tests on solid media. P. putida TSh-18 is recommended as a sensor system for ampicillin detection. Electro-optical analysis ensures detection of ampicillin in aquatic solutions in real-time, takes 10 min, and offers a lower limit of ampicillin detection of 0.5 μg/mL, which is lower than the European Community's maximum residue limit standards for penicillin antibiotics.

Performance Analysis of Space Surveillance Using Space Based Optical Sensors

This paper aims to describe the analysis of the performance of an electro-optical space-based sensor for space surveillance purposes and space debris detection in the geostationary (GEO) ring. Such sensor is considered to be operating on a dawn–dusk Sun-synchronous, circular low Earth orbit at an altitude of 630 Km, while its optical characteristics have been taken from those of the Space-Based Visible (SBV) sensor. Two main simulations have been carried out through the use of the MATLAB software. The first simulation deals with the detection capability of the sensor, which is discussed in terms of detectable visual magnitude when the target of the observation is a diffuse sphere orbiting in the geostationary (GEO) orbit; its minimum detectable size is then determined. In addition, the relative geometry between the Sun, the sensor and the target has also been studied along with the configurations which can limit the visibility of the sensor over the target. The second simulation has been used to evaluate the performance of the sensor in terms of number of detectable GEO targets and duration of the observation when a certain pointing strategy is adopted. In such strategy, two SBV-like sensors are placed on the same orbit, thus creating a constellation in which each sensor points towards a fixed location in the inertial space. These locations have been chosen to be the geosynchronous pinch points.

On the realization and analysis of circular harmonic transforms for feature detection

Circular-harmonic spectra are a compact representation of local image features in two dimensions. It is well known that the computational complexity of such transforms is greatly reduced when polar separability is exploited in steerable filter-banks. Further simplifications are possible when Cartesian separability is incorporated using the radial apodization (i.e. weight, window, or taper) described here, as a consequence of the Laguerre/Hermite correspondence over polar/Cartesian coordinates. The chosen form also mitigates undesirable discretization artefacts due to angular aliasing. The possible utility of circular-harmonic spectra for the description of simple features is illustrated using real data from an airborne electro-optic sensor. The spectrum is deployed in a test-statistic to detect and characterize corners of arbitrary angle and orientation (i.e. wedges). The test-statistic considers uncertainty due to finite sampling and clutter/noise.

Electro-optical detection of terahertz radiation in a zinc sulphide crystal at a wavelength of 512 nm

The electro-optical sampling method is a widely used technique for the detection of terahertz (THz) waves. During the last thirty years, various electro-optical sensors have been proposed, but mainly working with a near-infrared probe. Here we demonstrate efficient detection of terahertz radiation up to 2.5 THz using a (110)-cut zinc sulfide (ZnS) crystals with the second harmonic of an amplified solid-state ytterbium laser beam at 512 nm. To validate its characteristics, we compare its performance with that of the cadmium telluride (CdTe) crystal probed at the fundamental wavelength of the laser.

Comprehensive comparative evaluation of background subtraction algorithms in open sea environments

In autonomous-ship and maritime security surveillance operations involving electro-optical sensors, the first phase of foreground segmentation and change detection using background subtraction (BS) algorithms is crucial. However, it is also the most complex in terms of execution time. Despite the development of several BS algorithms, maritime foreground segmentation and change detection remain major challenges owing to the complex, unconstrained, and diverse nature of ocean scenarios. However, only a few studies have investigated the applications of BS algorithms in maritime environments, especially those involving boats in the open sea. This study compares BS methods involving use of a non-static electro-optical sensor in combination with visible-light and infrared cameras to identify the best method for use in open sea scenarios, especially from the viewpoint of avoiding piracy and armed robbery. Thirty-seven methods, ranging from simple temporal differencing to more sophisticated ones, were validated via extensive experiments and analyses using realistic maritime datasets and practical maritime applications. In addition, because most methods considered in this study were not previously evaluated at the pixel level on open sea datasets, this paper proposes an appropriate maritime BS benchmark, based on which the 37 methods were compared to compensate for their prior lack of detailed analyses. The experimental results indicate that BS algorithms of the multiple features category can better handle maritime challenges, thereby realizing higher accuracies when analyzing visible-light and thermal videos. The proposed evaluation, therefore, complements those reported previously. Consequently, the proposed study enables users to identify the most suitable BS algorithm for use in intelligent maritime transportation, maritime security surveillance systems, and autonomous ships in the open sea.

Method of preliminary solution of the problem of space robot navigation by onboard astronomical measurements using the butterworth filter

A method of preliminary solution of the problem of space robot navigation based on the results of measurements carried out using its onboard optronic equipment is presented. The initial data of the navigation problem are the directional cosines of the space robot orientation vector in the absolute geocentric equatorial coordinate system with reference to time during one revolution. Analytical expressions are obtained for determining unknown parameters of the motion of the space robot center of mass in the form of Keplers elements of the orbit. It is shown that to determine the right ascension of the ascending node, the inclination and the semi-major axis of the orbit of the space robot, information about the orientation of its radius vector at various times is used, and to determine the perigee argument, the moment of passing the perigee and the eccentricity of the orbit, the angular orbital speed of the space robot is used, which is determined by the results of evaluating the speed of change in the orientation of its radius vector over time. The presented results can be used in the development of software for navigation systems that allow autonomous determination of the parameters of the space robots orbit using onboard electro-optical sensors in the absence of a priori information about the parameters of the reference orbit or signals from satellite radio navigation systems.