Target Reflectivity Research Articles

Acoustic reflector utilizing sound speed control by multiple obstacles

Acoustic diffusers have a structure that diffuses sound waves in various directions by utilizing the interference of sound waves caused by surface irregularities. For example, a phase diffraction grating based on number theory has a structure with equally spaced depressions of irregular depth, and the maximum difference between the depressions is half the target wavelength. If the reflector targets 500 Hz sound waves, the thickness of at least 34 cm is required. On the other hand, the acoustic lens proposed by Kock et al. in the 1950s composed by multiple spheres or other obstacles to control the speed of sound. This report proposes a diffuser without depressions of irregular depth by applying the acoustic lens principle of Kock etal. The difference in reflection time caused by the depressions of the diffuser can be controlled by multiple obstacles.

Supercontinuum-based hyperspectral LiDAR for precision laser scanning.

Hyperspectral LiDAR enables non-contact mapping of the 3D surface geometry of an object along with its spectral reflectance signature and has proved to be effective for automated point cloud segmentation in various remote sensing applications. The established hyperspectral LiDAR methods offer a range precision of a few mm to a few cm for distances exceeding several meters. We propose a novel approach to hyperspectral LiDAR scanning based on a supercontinuum (SC) coherently broadened from a 780 nm frequency comb. It provides high precision distance measurements along with target reflectance over the 570-970 nm range of the SC output. The distance measurements are carried out by monitoring the differential phase delay of intermode beat notes generated by direct photodetection, while the backscattered light spectrum is acquired using a commercial CCD spectrometer with 0.16 nm resolution across the 400 nm bandwidth of the SC output. We demonstrate a measurement precision below 0.1 mm for a stand-off range up to 50 m on a diffuse target with around 89% reflectance. The measured relative accuracy as compared to a reference interferometer is on the order of 10-5 for distances up to 50 m. Initial results also indicate spectrum-based material classification within a 3D point cloud using a linear support vector machine. The results highlight the potential of this approach for joint high-precision laser scanning and automated material classification.

Identification of carbonate cave reservoirs using wavelet reconstruction and WLRPCA based background modeling

Carbonate cave reservoirs are controlled by large strike-slip fault, which are home to incredibly rich oil and gas resources and hold immense exploration potential. The effective identification of these reservoirs using geophysical methods is quite important, but often challenging due to low signal-to-noise ratio and strong background reflection shielding of raw seismic data. In order to fully exploit the information of carbonate reservoirs contained in seismic data and improve the interpretation accuracy, we involve the innovative use of wavelet reconstruction and background modeling techniques to enhance the identification accuracy of carbonate cave reservoirs based on post-stack seismic data. The wavelet reconstruction in the first step mitigate the impact of noise and background reflection, allowing us to reveal the bead-like reflections hidden underneath strong interference energy. Then, we propose a background modeling method based on the weighted logarithmic robust principal component analysis (WLRPCA) technique in the second part to further eliminate background and noise signals. Compared with traditional principal component analysis (PCA) and robust principal component analysis (RPCA), WLRPCA exhibits superior recognition accuracy and noise immunity in the background modeling process, which effectively separates the target reflection from interference reflection and provides a favorable data basis for subsequent reservoir identification. Finally, a comprehensive attribute analysis is conducted on the processed seismic data, which confirms that the sweetness is the most effective attribute in detecting cave reservoirs. The proposed method has been successfully applied to both synthetic data and real data from an oil field in northern China, demonstrating their feasibility and effectiveness in identifying carbonate cave reservoirs.

Underwater spectral reflectance measurements: the reflectance standard submersion factor and its impact on derived target reflectance.

For Earth observation remote sensing, high quality reflectance spectra are necessary for model input, algorithm development, and validation of derived products. In the aquatic environment, a common approach for making spectral reflectance measurements involves using a calibrated reflectance standard such as a Spectralon plaque underwater. The manufacturer provides a National Institute of Standards and Technology traceable reflectance curve with each standard, measured in air. Here, we demonstrate how the reflectance factor changes when submerged in water based on the standard albedo and viewing geometry. Target reflectances calculated incorrectly with the air calibrated values are 10%-60% lower than those estimated with submerged plaque calibrations. We provide guidelines for proper use and calibration of standards underwater.

Evaluating the effects of material reflectivity and atmospheric attenuation on photonic radar performance in free space optical channels

Abstract The automotive industry is on the verge of embracing autonomous vehicles in the near future. In the pursuit of developing self-driving cars, photonic radars have emerged as a reliable sensor technology. These radars operate based on free space optical channels, but they are vulnerable to various atmospheric challenges. In this research, the objective is to examine the effect of material reflectivity on target recognition by utilizing photonic radar under various atmospheric conditions within free space optical channels. We explore four distinct scenarios representing targets with reflectivity ranging from 90 % to 20 %. The findings of this study indicate a decrease in received signal strength as reflectivity decreases across all analysed atmospheric conditions. The key findings include successful detection of stationary targets at a 1000-m range, the impact of target reflectivity on echo signal intensity and resolution, and the system’s effective performance in detecting targets even in dense fog conditions of up to 50 dB/km and are further validated through theoretical analysis.

Polarization- and angle-insensitive broadband long wavelength infrared absorber based on coplanar four-sized resonators.

In many potential applications, there is a high demand for long wavelength infrared (LWIR) absorbers characterized by a compact configuration, broad operational bandwidth, high absorption efficiency, and polarization- and angle-insensitive characteristics. In this study, we design and demonstrate a high-performance broadband LWIR absorber based on coplanar four-sized resonators, consisting of arrays of titanium (Ti) disks with different diameters supported by a continuous zinc selenide (ZnSe) layer and by a Ti film acting as a back-reflector. Particle swarm optimization (PSO) is employed to optimize the complicated geometry parameters, and the final optimized device exhibits near-unity absorption (∼96.7%) across the entire operational bandwidth (8 µm∼14 µm) under unpolarized normal incidence, benefiting from the impedance-matching condition and the multiple surface plasmon resonances of this configuration. Furthermore, the proposed absorber is insensitive to the angle of incidence due to the localized surface plasmon resonances supported by these four-sized resonators, and is insensitive to the state of polarization thanks to the highly symmetric feature of the circular pattern. The measured absorption of the fabricated sample exhibits a relatively high coincidence with the simulation, with an average absorption of 88.9% ranging from 8 µm to 14 µm. The proposed absorber, which can be easily integrated into a standardized micro/nano manufacture process for cost-effective large-scale production, provides a feasible solution for improving optical performance in thermal emitter, infrared detection, and imaging applications. Furthermore, the generalized design principle employing the optimized method opens up new avenues for realizing target absorption, reflection, and transmission based on more complicated structure configurations.

High-availability displacement sensing with multi-channel self mixing interferometry.

Laser self-mixing is in principle a simple and robust general purpose interferometric method, with the additional expressivity which results from nonlinearity. However, it is rather sensitive to unwanted changes in target reflectivity, which often hinders applications with non-cooperative targets. Here we analyze experimentally a multi-channel sensor based on three independent self-mixing signals processed by a small neural network. We show that it provides high-availability motion sensing, robust not only to measurement noise but also to complete loss of signal in some channels. As a form of hybrid sensing based on nonlinear photonics and neural networks, it also opens perspectives for fully multimodal complex photonics sensing.

Polarised full-waveform warning LIDAR with dust backscattering suppression

LIDAR, when used under adverse weather conditions such as fog and dust, suffers from attenuation and backscattering. In particular, backscattering creates spurious echo peaks in the received waveforms at incorrected ranges and leads to false alarms. As a solution, this paper proposes polarised full-waveform warning LIDAR for dust backscattering echo suppression, intended for applications under dusty environments. To this end, first, a theoretical model of the polarised LIDAR is developed based on the LIDAR equation and depolarisation characteristics of dust backscattering and target reflection. Thereafter, the depolarisation characteristics are experimentally evaluated under an artificially generated dusty environment; the results reveal that the target reflection features a strong depolarisation characteristic, whereas dust backscattering has a weak one. When the LIDAR emits linearly polarised light, a significant orthogonal-polarised component exists owing to the target reflection, and dust backscattering induces a mainly parallel-polarised component. On interposing an orthogonal-polarisation analyser in the receiving optical path, the parallel-polarised component from the dust backscattering and target reflection is blocked, whereas the orthogonal-polarised component is allowed to pass; this helps improve the contrast of the target reflection to dust backscattering. Finally, based on the theoretical model of the polarised LIDAR and experimental results, an orthogonal-polarised LIDAR prototype is designed and fabricated. Using this prototype, target detection experiments in a dusty environment are performed; the corresponding experimental results indicate that the orthogonal-polarised LIDAR effectively suppresses dust backscattering echoes and that the contrast of the target reflection to dust backscattering is improved by 4.78–7.12 dB. Utilization of the polarised full-waveform warning LIDAR can significantly reduce the false alarm rate and improves the LIDAR system performance when used under dusty environment conditions, in applications such as smart mining and autonomous driving.

All-in-One SPAD Ranging Sensor With Real-Time Xtalk Calibration and Integrated Biasing

This letter presents a novel fully integrated dToF system-on-chip ranging sensor based on a SPADs array. The sensor is made a configurable array of 16 × 16 SPADs, a 940nm VCSEL, a co-design VCSEL driver and embedded DSP core. To suitable different ranging scenarios with high reliability and low cost, the above mentioned are all packaged into one module for ranging. However, the package of coverglass can cause Xtalk, which have a negative impact on ranging. In order to reduce the influence of Xtalk on ranging. This letter proposes a real-time Xtalk calibration circuit system, which can automatically adjust the laser pulse width, when Xtalk and target bins are mixed together. And also to mitigate the effect of SPAD jitter on the Xtalk bins width, an adjustable bias voltage charge pump circuit is adopted to realize the accurate adjustment of pixel SPAD’s bias voltage. The system has been turned out with precision of better than 5mm within 6m in 80% reflectance of target, still with a precision better than 8mm at a distance within 4m in 18% reflectance of target.

Quantifying amplitude-variation-with-offset uncertainties related to calcite-cemented beds using a Monte Carlo simulation

Calcite cement often occurs locally, forming thin layers of calcite-cemented sandstone characterized by high seismic velocities and densities. Because of their strong impedance contrast with the surrounding rock, calcite-cemented intervals produce detectable seismic reflection signals that may interfere with target reflections at the top of a reservoir. In this case, the amplitude-variation-with-offset (AVO) of the effective seismic signature will be altered and may even create a false hydrocarbon indication. From the Monte Carlo simulation, we find that the presence of thin calcite-cemented beds increases the uncertainty of the Bayesian pore-fluid classification based on the AVO attributes intercept and gradient. In the case example of a North Sea turbiditic oil and gas field, the probability of a false-positive hydrocarbon indication increases from 3%–5% to 18%–21% assuming an equal probability of the occurrence of brine, oil, and gas. The results confirm that calcite-cemented beds can create a pitfall in AVO analysis. Realistic estimates of the AVO uncertainty are crucial for the risk assessment of well placement decisions.

Sonar Point Cloud Processing to Identify Sea Turtles by Pattern Analysis

Abundant in coastal areas, sea turtles are affected by high-intensity acoustic anthropogenic sounds. In this article, we offer a pattern-analysis-based detection approach to serve as a warning system for the existence of nearby sea turtles. We focus on the challenge of overcoming the low signal-to-clutter ratio (SCR) caused by reverberations. Assuming that, owing to low SCR, target reflections within the point cloud are received in groups, our detector searches for patterns through clustering to identify possible “blobs” in the point cloud of reflections, and to classify them as either clutter or a target. Our unsupervised clustering is based on geometrical and spectral constraints over the blob's member relations. In turn, the classification of identified blobs as either a target or clutter is based on features extracted from the reflection pattern. To this end, assuming that reflections from a sea turtle are stable but include spectral diversity due to distortions within the turtle's body, we quantify the stability of the blob's members and the entropy of their reflection spectrum. We test our detector in both the modeled simulations, and at sea, for the detection of sea turtles released after rehabilitation. The results show robustness to highly fluctuating target intensity and ability to detect at low SCR.

High School EFL Teachers’ Continuous Professional Development: Target Needs, Reflection and Challenges

This research investigated the high school EFL teachers’ continuous professional development target needs, reflection and challenges. Further, the target needs of the EFL teachers were analyzed by adapting Hutchinson and Waters’ model (1987). The data were collected using a test, questionnaire (consisted of five parts), and interview; these were administered to 20 high school EFL teachers. A test was administered to identify EFL teachers' present situation and difficulties, and questionnaire parts 1, 2 and 4 dealt with the EFL teachers' difficulties, needs and purposes in the program. Moreover, these were used to identify EFL teachers’ target needs centered on their lacks, necessities, and wants to function in the target situation effectively. Parts 3 and 5 concerned high school EFL teachers' reflection and challenges in the professional development program they are involved in.Additionally, interviews were conducted with the high school EFL teachers to gather data to examine in-depth results of the target needs, reflections and challenges. The results suggested that the high school EFL teachers have different views of their lacks, wants and necessities. The findings also demonstrated that the high school EFL teachers reflected that the current professional development program practicing in their school was never conducted to help EFL teachers develop their profession. Finally, the result revealed that high school EFL teachers face various challenges in the current program they are taking. Therefore, the professional development should be revised according to EFL teachers’ target needs, reflections and challenges.

직선형 파동유도관에서 벽면 쐐기의 길이에 따른 초음파 전파

This study focuses on the ultrasonic propagation along the wedge length of the wall in a straight waveguide designed to reduce the minimum detection distance of an ultrasonic sensor for distance measurement. Wedges are created on the waveguide wall to avoid ultrasound interference caused by reflection on a smooth wall, and the wedge dimensions must be chosen carefully. The magnitude of the ultrasonic signal was evaluated according to the wedge length in terms of the ratio of the target reflection to the exit reflection while maintaining the wedge angle selected in the previous study. The propagation of ultrasonic waves was studied using finite element analysis. The wedge length that maximizes the magnitude of the ultrasonic signal was found to be similar to the wavelength. It was possible to reduce unwanted reflection and increase target reflection by adjusting the waveguide wall wedge length.

METHOD OF SELF-DEFENSE OF GROUND (SURFACE) OBJECTS FROM HIGH-PRECISION RADAR MEANS OF AIR SURVEILLANCE

Context it is caused by the need to search for scientific and technical ways to ensure the effectiveness of protecting ground (surface) objects from high-precision guided missile weapons.
 Objective it is a necessity to ensure effective self-defense of objects from radar homing means.
 Method. Electrodynamic modeling of Echo signals from spatially distributed objects, taking into account the features of their design and related operational limitations.
 Results. Based on the analysis of the shortcomings of the well-known method of protecting stationary objects from radar surveillance and damage, based on the simulation of an effective reflection center outside the physical dimensions of the object, a new method of countering high-precision measurement of coordinates of stationary and mobile ground (surface) objects is proposed. The technique is based on the spatial deformation of the location of the effective target reflection center with dynamics that exceed the inertial capabilities of the auto-observation contour of the attacking missile (projectile). A structural and functional scheme of technical implementation of the methodology based on the first proposed relationship of simple design and technological solutions is proposed and justified.
 Conclusions. The analytical model of Echo signals of spatially distributed ground (surface) objects was further developed, which takes into account the specifics of their design, and on its basis, for the first time, a universal method of self-defense of objects from radar home-leading devices was developed, which is implemented in a patented method and complex to exclude damage to protected objects.

High School EFL Teachers’ Continuous Professional Development: Target Needs, Reflection and Challenges

This research investigated the high school EFL teachers’ continuous professional development target needs, reflection and challenges. Further, the target needs of the EFL teachers were analyzed by adapting Hutchinson and Waters’ model (1987). The data were collected using a test, questionnaire (consisted of five parts), and interview; these were administered to 20 high school EFL teachers. A test was administered to identify EFL teachers' present situation and difficulties, and questionnaire parts 1, 2 and 4 dealt with the EFL teachers' difficulties, needs and purposes in the program. Moreover, these were used to identify EFL teachers’ target needs centered on their lacks, necessities, and wants to function in the target situation effectively. Parts 3 and 5 concerned high school EFL teachers' reflection and challenges in the professional development program they are involved in. Additionally, interviews were conducted with the high school EFL teachers to gather data to examine in-depth results of the target needs, reflections and challenges. The results suggested that the high school EFL teachers have different views of their lacks, wants and necessities. The findings also demonstrated that the high school EFL teachers reflected that the current professional development program practicing in their school was never conducted to help EFL teachers develop their profession. Finally, the result revealed that high school EFL teachers face various challenges in the current program they are taking. Therefore, the professional development should be revised according to EFL teachers’ target needs, reflections and challenges.

Optimization of Mismatched Filters With Asymmetric Side-Lobe Shape for Short-Range MIMO Radars

This paper presents the design of signal compression and separation filters with asymmetric responses for multiple-input multiple-output (MIMO) radars that use pulses longer than the maximum return time of the reflected signal. Such radars suffer from direct penetration of the transmitted signal to the receiver, appearing as a very strong stationary reflection in the zero range. After pulse compression, the far-side lobes of this crosstalk may compete with the reflections of distant weak targets and limit the maximum radar range. Hence, in addition to the maximum suppression of the direct transmitted signal penetration to the receiver, the far-side lobe reduction of this crosstalk with positive time lags is desirable. Asymmetric response filters allow optimization to be focused on the region where the maximum suppression of crosstalk between the transmitted signal and the receiver is desired. Extreme suppression was achieved by applying lower demand in other areas and other parameters. In this paper, the problem is described in more detail along with the mathematical apparatus by which asymmetric filter outputs can be achieved.

DOA Signal Identification Based on Amplitude and Phase Estimation for Subarray MIMO Radar Applications

The overlapped equal subarray transmit radar, which is also known as the Subarray Multiple-Input Multiple-Output radar, utilizes the key advantages simultaneously of both types of multi-antenna radar, i.e. the phased array and MIMO radars, so that it is able to detect multiple targets even though it has a radar cross section (RCS) of a weak or small target. In this paper, it is proposed to develop a parameter estimation approach called amplitude and phase estimation (APES). This approach provides improved resolution to the estimation of the amplitude and direction of arrival (DoA) of the target reflection signal on the radar compared to the existing conventional estimation methods such as least squares (LS). The formulation of the APES method on this radar is based on the tested parameters such as DoA and RCS and continuously being evaluated. The results show that the performance of the APES method of this radar can detect targets very precisely when the number of subarrays (M) is greater than the number of detection targets (P), precisely M > P. For the results of DoA and RCS accuracy from the APES method, this radar is more accurate than the LS when testing the angular resolution between the two targets, an angle resolution of 2° is obtained for the APES method which is superior to the LS with an angle resolution of 5.8°. In these conditions, the APES method is able to accurately distinguish between two targets while the LS method is only able to detect one target.

Using dictionary learning for clutter reduction in GPR B-scan images

ABSTRACT Ground-penetrating radar (GPR) has been widely used to detect subsurface objects. However, the target reflection experiences interference owing to clutter, such as direct coupling, interface reflection, and other undesired reflections. Reducing such clutter is a valuable processing step to improve detection accuracy. This letter proposes a GPR clutter reduction algorithm based on dictionary learning (DL). DL learns an adaptive dictionary that can sparsely represent the GPR B-scan image and enable clutter suppression. The learned dictionary atoms are divided into target atoms and clutter atoms, the target component and the clutter component can be reconstructed using these two types of dictionary atoms, respectively. The performance of the proposed algorithm is validated using both simulation data and real GPR data. The results of the visual evaluation and quantitative analysis demonstrate that the proposed algorithm outperforms the existing clutter reduction algorithms.

Beam resource scheduling for a VHF-MIMO radar network in low-angle tracking

The low-angle tracking in multipath interference is a challenging problem for the Very High Frequency (VHF) radar. The colocated Multi-Input Multi-Output (MIMO) technique can remedy such a defect. In this paper, a Joint Beam-Target Assignment and Power Allocation (JBTAPA) strategy is proposed for the VHF-MIMO radar network tracking low-angle targets. The core of the JBTAPA strategy is to improve the worst tracking accuracy among multiple targets by assigning appropriate beams to targets and allocating the power resource in each beam using the feedback information in the tracking cycle. Taking into account the transmit multipath and receive multipath, we derive the Cramér-Rao Lower Bound (CRLB) on angle estimate, which is then incorporated in the Predicted Conditional CRLB (PC-CRLB). A more accurate and consistent lower bound is provided as the optimization metric since the PC-CRLB is based on the most recently realized measurements. A two-stage-based technique is proposed to solve the JBTAPA problem, which is originally NP-hard. Simulation results verify the effectiveness and efficiency of the proposed method. The results also imply that the target reflectivity plays one of the important roles in resource allocation.

Design and Implementation of a Ku-Band High-Precision Blackbody Calibration Target.

Microwave radiometers can be used in human tissue temperature measurement scenarios due to the advantages of non-destructive and non-contact temperature measurement. However, their accuracy often cannot meet the needs of practical applications. In this paper, a Ku-Band high-precision blackbody calibration target is designed to provide calibration for microwave radiometers and meet the requirements of a high temperature-measurement accuracy and high temperature-measurement resolution. From a practical application point of view, the blackbody calibration target needs to have the characteristics of high emissivity and high temperature uniformity. However, previous studies on blackbody calibration targets often focused on the scattering characteristics or temperature uniformity of the calibration target separately, and thus lack a comprehensive consideration of the two characteristics. In this paper, the electromagnetic scattering model and the temperature-distribution model of the calibration target are established through the multi-physical simulation combined with the Finite Element Method. Then, according to the simulation results of the two characteristic models, the structural parameters and composition of the coated cone array are continuously optimized. In addition, to achieve high-precision temperature control of the blackbody calibration target, this paper studies three PID controller parameter self-tuning algorithms, namely, BP-PID, PSO-PID and Fuzzy-PID for the optimal parameter tuning problem of traditional PID algorithms and determines the optimal temperature-control algorithm by comparing the performance of heating and cooling processes. Then, the blackbody calibration target is processed and manufactured. The arch test system is used to validate the reflectance of the calibration target, the emissivity is calculated indirectly, and the temperature-distribution uniformity of the temperature-control panel of the calibration target is tested by a multi-point distribution method. Finally, the uncertainty of the brightness temperature of the blackbody calibration target is analyzed.