Sight Angle Research Articles

Line-of-sight rate construction for a roll-pitch gimbal via a virtual pitch-yaw gimbal

In this paper, a method to construct the line of sight rate of a target with a roll-pitch gimbal and tracker is described. Construction of line-of-sight rate is performed via utilizing a virtual pitch-yaw gimbal. Kinematics of both the roll-pitch and pitch-yaw gimbals are described. A dynamical model for the roll-pitch gimbal is developed, and a nested control structure is designed to control the angular rates and line of sight angles. A kinematic model of the tracker is developed and a tracker controller is designed to keep the target in the field of view. Conversion equations between roll-pitch and pitch-yaw gimbal configurations are provided. Finally, constructed line of sight rates are compared to true line of sight rates via simulations. Obtained results indicate that the constructed line of sight rates pertaining to a target satisfactorily converge to the actual line of sight rates.

Спотворення зображення в системах дистанційного зондування Землі при довільних кутах візування

Background. The main problem in launching space optical and electronic viewing systems (OEVS) for remote sensing of the Earth can be regarded as their high price, which even the leading countries of the world are not always ready to pay. Therefore, the quality of spacecraft systems imposed the most stringent requirements. One of the economically expedient options to increase the efficiency of space OEVS is scanning the Earth’s surface at arbitrary angles of sighting, which allows for the same time of service life to collect more information, but this in turn leads to image distortion. Therefore, analysis of the resulting image quality depending on the angles of sighting of the OEVS is an actual task that will assess the capabilities of the system and its conformance with the established requirements. Objective. Improving the physical and mathematical model of the modulation transfer function of the system “lens – matrix detector” and the study of the dependence of spatial and radiometric resolution on the angles of sight for the space OEVS when the sighting axis deviates from the nadir. Methods. Based on the analysis of signal generation models for television and thermal imaging space OEVS, it is proposed to use the concept – the contrast gray body. In the physical and mathematical model, it is proposed normalize to the spatial frequencies of objects at different angles of sight to the spatial frequencies in the nadir, and to calculate the radiometric resolution take into account the transmission and rarefied of the atmosphere, the image movement speed on the detector and its integration time. Results. Practical results of calculations of the offered physical and mathematical model for space OEVS showed that at deviation from nadir the effective spatial bandwidth worsens and at the specified parameters of system it is inexpedient scanning at angles of sighting greater than 30º. Accordingly, a comparative analysis of radiometric resolution for different type of detectors showed that the use of a photonic detector gives ~1.4 times better resolution in the nadir as opposed to the use of thermal detector and almost identical results are obtained at maximum angles of sighting. Also, a significant impact is made by a decrease a coefficient of atmospheric transmittance due to the rarefied of the atmosphere, which reaches from 26% to 45% that depends on the spectral range. Conclusions. Analysis of the results of the study confirms the possibility that photonic detectors can be replaced by modern thermal detectors with insignificant loss of image quality of the resulting image, which can significantly increase the service life of space OEVS.

Flight safety event management method as illustrated by a guided reactivity model

The article provides a brief analysis of the problems of the existing flight safety management system in the state aviation of the Russian Federation, based on the lack of stable positive dynamics of accidents reduction. Brief conclusions from the analysis of the currently proposed scientific approaches for accidents reduction are given. The most significant practical results in the field of building a safety management system for a particular flight are considered. A new approach to the implementation of on-board flight safety management systems based on event management is proposed. The method of event-based safety management of a particular flight allows us to exclude the real time manifestation of known dangerous factors. To implement it, all processes related to known hazards are described in the form of events and assembled into complete groups of events. Control of the occurrence of the complete groups of events, their analysis and event management are carried out by event management models developed for each dangerous factor. When a certain number of events in one or several complete groups of events is reached, the aviation system protection algorithm, by preventing the occurrence of the remaining one or several events of the complete group, prevents erroneous actions of the crew, which prevents the occurrence of aviation incidents and accidents. As an example of the method implementation, the principle of forming an automated guided reactivity model of the event control contour for the dangerous factor "Violation of the Established Minimum Safe Parameters of the Aircraft Flight" in relation to an arbitrary maneuverable aircraft is considered in the article. The system, having registered the events that determine the group flight, is included into the analysis of dynamic elementary events determining the position of the wingman relating to the leading aircraft inside the event control contour in terms of range, angle of sight and altitude separation. When the parameters of one of the dynamic events approach the boundary of the event control contour, the system uses a recommendation or control action to set limits to the parameters not to go beyond the contour, which prevents the occurrence of erroneous actions of the crew.

Systematic approach of guidance information reconstruction of laser strapdown guidance air-to-ground missile

The decoupling algorithm of laser strapdown guidance which can effectively suppress the disturbance rejection rate problem and a method of extracting line of sight angle rate are studied. Firstly, the decoupling mathematical model of strapdown seeker is established, the cause of the disturbance rejection rate problem of strapdown guidance is analyzed, and the time synchronization algorithm is designed to reduce the coupling of the attitude motion of the missile to the guidance information. Secondly, an extraction algorithm of line of sight angle rate is established, an extraction algorithm of filter parameters changing with the remaining flight time is designed to suppress the attitude oscillation of the initial phase of terminal guidance and improve the tracking speed of the last phase, and the extracted line of sight angle rate is compared with the output characteristics of the platform seeker. Finally, the effectiveness of the proposed line of sight angle rate extraction algorithm is verified by six degrees of freedom trajectory simulation, and the influence of disturbance rejection rate parasitic loop on strapdown terminal guidance accuracy is analyzed by simulation.

Target Tracking Enhancement by Three-Dimensional Cooperative Guidance Law Imposing Relative Interception Geometry

The problem that two cooperative missiles intercept a maneuvering target while imposing a desired relative geometry is investigated in the paper. Firstly, a three-dimensional (3D) estimation model for cooperative target tracking is proposed and the observability of the missile-target range measurement is analyzed. In order to enhance the estimation performance, a two-level cooperative interception guidance architecture is proposed which combines a coordination algorithm with a novel 3D fixed-time convergent guidance law considering line of sight (LOS) angle constraints, such that the desired relative geometry can be imposed quickly and steadily by a dynamic strategy. The effectiveness and superiority of the proposed guidance law is evidenced through the numerical simulations comparing with other guidance laws.

Three-dimensional sliding mode guidance law for maneuvering target with prescribed performance and input saturation

The three-dimensional sliding mode guidance laws with prescribed performance and saturation actuator are proposed for maneuvering target. The proposed guidance laws can ensure the line of sight (LOS) angle converges according to the prescribed performance with actuator saturation and the convergence rate, the steady state error and the maximum overshoot can be preset in advance. A novel transformed error function is designed by combining the LOS tracking error with the performance constraint function. Then, to further solve the problem of input saturation, the saturation function and auxiliary system are introduced. Additionally, this paper discusses the problem whereby the upper bound of the aggregate uncertainty, including the target information, is unavailable. An adaptive sliding mode guidance law with prescribed performance is presented for this scenario. Experiments comparisons are conducted with other forms of guidance laws. Simulation results show that the guidance laws proposed in this paper achieve effective performance.

Detection Effectiveness Estimation Based on Multi-Angle Data and Visualization Analysis

In intelligent confrontation games, how to estimate the detection effectiveness of the early-warning detection (EWD) system of systems (SoS) is the most important issue that has been studied in hopes of a breakthrough for the long time. The conventional approaches to effectiveness estimation have been reductionism or the linear estimation methods, which are not suitable for the estimation of the effectiveness of EWD SoS. Effectiveness estimation methods and ideas based on complex networks have been proposed and studied, which can inspire that the logic relationship in the SoS can be analyzed by using the network thoughts. As a development of some research based on the Data mode, data and visualization analysis methods have been proposed. In these approaches, the multi-angle data and visualization analysis methods can be utilized to directly show some significant relationships in the SoS from the different aspects, especially from different angles of sight. These statistics and suggested results can be employed to analyze the situation of SoS, so they have potentially important capabilities in terms of the estimation of EWD SoS. Therefore, in this paper, these new ideas are introduced into the study and solution of the problem of the detection effectiveness estimation of EWD SoS. On the basis that the running characteristics of the detecting work of the EWD SoS are described, the data method and idea with multi-angles for EWD SoS are proposed and discussed, and the visualization analysis method and ideas about EWD SoS are suggested and analyzed. Furthermore, a typical application is employed to estimate the detection effectiveness of EWD SoS, based on the data and visualization analysis methods stated in this paper. As the results of the estimate are generally consistent with the actual situation, the validity of the proposed methods is considered proven. The main work in this paper can provide new ideas on the study of the issue of the detection effectiveness estimation of EWD SoS, and it also helpful for SoS analysis and other estimations of effectiveness.

SAR Image Registration in the Presence of Rotation and Translation: A Constrained Least Squares Approach

This letter proposes a coregistration algorithm to compensate for the possible inaccuracy of trajectory sensor during the synthetic aperture radar (SAR) image acquisition process. Such a misalignment can be modeled as a pure displacement in range and azimuth directions and a rotation effect due to different angles of sight. The approach is formalized as a constrained least squares (CLS) optimization problem enforcing a constraint of the absence of a zooming effect between the two SAR images. Moreover, the system equations can optionally be weighted according to local properties between the extracted patches within the quoted couple. Interestingly, the solution can be obtained in closed form, therefore, with a low computational cost. The results of the tests conducted on the 9.6-GHz Gotcha SAR data demonstrate the capability of the strategy to properly register the imagery.

The Microvariable Activity of BL Lacertae

We report on seven nights of optical observation taken over a two-week period, and the resultant analysis of the intermediate-frequency peaked BL Lac object (IBL), BL Lac itself, at redshift z = 0.069. The microvariable behavior can be confirmed over the course of minutes for each night. A relativistic beaming model was used in our analysis, to infer changes to the line of sight angles for the motion of the different relativistic components. This model has very few free parameters. The light curves we generated show both high and moderate frequency cadence to the variable behavior of BL Lac itself, in addition to the well documented long-term variability.

Integrated Guidance and Control Design of Rolling-Guided Projectile Based on Adaptive Fuzzy Control with Multiple Constraints

In the terminal guidance section of large caliber naval gun-guided projectile while striking nearshore maneuvering target, an integrated guidance and control (IGC) method based on an adaptive fuzzy and block dynamic surface sliding mode (AFCBDSM) was proposed with multiple constraints, including the impact angle, control limitations, and limited measurement of the line of sight (LOS) angle rate. The strict feedback cascade model of rolling-guided projectile IGC in space was constructed, and the extended state observer (ESO) was used to estimate the LOS angle rate and uncertain disturbances inside and outside the system, such as target maneuvering, model errors, and wind. A nonsingular terminal sliding mode (NTSM) was designed to zero the LOS angle tracking errors and LOS angle rate in finite time, with the adaptive exponential reaching law. The cascade system was effectively stabilized by the block dynamic surface sliding mode, which prevented differential explosions. To compensate for the saturated nonlinearity of canard control constraints, an adaptive Nussbaum gain function was adopted. The switching chatter of the block dynamic surface sliding mode was reduced through adaptive fuzzy control. Proven by Lyapunov theory, the LOS angle tracking error and LOS angle rate were convergent in finite time, the closed-loop system was uniformly ultimately bounded (UUB), and the system states could be made arbitrarily small at the steady state. Hardware-in-the-loop simulation (HILS) experiments showed that the AFCBDSM provided the guided projectile with good guidance performance while striking targets with different maneuvering forms.

Integrated guidance and control of guided projectile with multiple constraints based on fuzzy adaptive and dynamic surface

Based on fuzzy adaptive and dynamic surface (FADS), an integrated guidance and control (IGC) approach was proposed for large caliber naval gun guided projectile, which was robust to target maneuver, canard dynamic characteristics, and multiple constraints, such as impact angle, limited measurement of line of sight (LOS) angle rate and nonlinear saturation of canard deflection. Initially, a strict feedback cascade model of IGC in longitudinal plane was established, and extended state observer (ESO) was designed to estimate LOS angle rate and uncertain disturbances with unknown boundary inside and outside of system, including aerodynamic parameters perturbation, target maneuver and model errors. Secondly, aiming at zeroing LOS angle tracking error and LOS angle rate in finite time, a nonsingular terminal sliding mode (NTSM) was designed with adaptive exponential reaching law. Furthermore, combining with dynamic surface, which prevented the complex differential of virtual control laws, the fuzzy adaptive systems were designed to approximate observation errors of uncertain disturbances and to reduce chatter of control law. Finally, the adaptive Nussbaum gain function was introduced to compensate nonlinear saturation of canard deflection. The LOS angle tracking error and LOS angle rate were convergent in finite time and whole system states were uniform ultimately bounded, rigorously proven by Lyapunov stability theory. Hardware-in-the-loop simulation (HILS) and digital simulation experiments both showed FADS provided guided projectile with good guidance performance while striking targets with different maneuvering forms.

Assessing the impact of outside view on learning: a close look to EN 17037 ‘view out’ practices through the analysis of 220 classrooms

The purpose of design standards and guidelines is to ensure occupant safety and aid in occupant well-being and satisfaction. Educational buildings such as schools should extend this aim, by also promoting student learning, something that has triggered literature in the past suggesting significant correlation between learning performance and the indoor environment. EN 17037 “Daylight for Buildings” is a recently approved European standard that seeks to assess and ensure successful daylit spaces, including sections on protection against glare, exposure to sunlight, and view out. EN 17037 includes three ways of assessing view out in buildings including, Horizontal sight angle, Outside distance of the view, and Number of view layers outside of windows, a combination that potentially makes it an efficient way to describe such a complex concept. This paper will use a large data set of 220 K-12 classrooms in the Midwest region of the United States in order to evaluate whether any of these three levels of assessing view, or combinations of them can show potential effects on student achievement. The Number of view layers showed a significant positive effect on reading achievement. However, none of the metrics were found to be significant with respect to math achievement. These results aim to identify the next steps of a future controlled study towards a better quantifiable understanding of outside view perception, while also triggering a conversation about the main factors connected to outside view that should be considered towards an indoor environment that promotes learning and productivity.

Distributed cooperative encirclement hunting guidance for multiple flight vehicles system

Distributed cooperative encirclement hunting guidance strategy design and analysis issues for multiple flight vehicles system against a maneuvering target are considered in this paper. Distinct from the former results, the cooperative encirclement hunting guidance laws are based on the leader-follower coordination structure, and are divided into two parts. Firstly, for the leader flight vehicle, a full-head-on interception guidance law is proposed against the maneuvering target, where the uncertain dynamics and the target's unknown maneuver are estimated and compensated by using an extended state observer. For the follower flight vehicles, the distributed time-varying encirclement hunting line of sight angle formation tracking laws with overload saturation are designed where distributed extended state observers are introduced to approximate the complicated uncertain items and the leader vehicle's input signals. Then, the design processes of cooperative encirclement hunting guidance laws are summarized within five steps as an algorithm. Thirdly, the stability and the properties of the proposed cooperative encirclement hunting guidance algorithm are analyzed by employing Lyapunov theories. Finally, numerical simulation results illustrate the effectiveness of achieved cooperative encirclement hunting guidance strategies.

Extreme UV spectrometers for the tungsten 40–70 Å emission in the WEST tokamak

Since the decision to implement a tungsten (W) divertor in ITER, several tokamaks have introduced W in their plasma facing components. For these devices, W monitoring in the core plasma has thus become an important topic of research as its high radiation capability can lead to excessive radiative losses. We have used our extreme UV (EUV) grazing incidence spectrometer (GIS) to investigate the 40–70 Å range where W ions of intermediate charge emit in WEST tokamak discharges. The spectrometer is mounted on a mobile frame controlled with a jack so that it can measure the dependence of the brightness of any spectral feature lying in the observed wavelength interval as a function of the line of sight angle. The quasi-continuum and W line brightnesses in the 40–70 Å range are shown to be much larger when the observed region has a temperature above 3 keV . The brightness profiles as a function of the line of sight position also provides qualitative information on the emitting ions. The delivery and the current installation of a new imaging EUV spectrometer dedicated to the 40–70 Å range are reported. This spectrometer will allow to image the lower inner half of the plasma with an expected time resolution down to 10 ms. The absolute brightness calibration will be performed before the spectrometer is installed on the tokamak at the beginning of the coming experimental campaign.

Morphology of the Small Magellanic Cloud using multiwavelength photometry of classical Cepheids

ABSTRACT This is the second of a series related to the study of geometry of the Magellanic Clouds based on multiwavelength photometry of classical Cepheids. In this paper we determine the geometrical and viewing angle parameters of the Small Magellanic Cloud (SMC) using the Leavitt law for classical Cepheids with/without a break in the law at a certain period as reported in the literature. The study utilizes photometric data for more than 3400 common classical Cepheids (Fundamental (FU) and First overtone (FO)) in optical (V, I), near-infrared (Y, J, Ks) and mid-infrared ([3.6] and [4.5] μm) photometric bands. We obtain statistical reddening and distance modulus free from the effect of reddening to each of the individual Cepheids with respect to the mean distance modulus and reddening of the SMC. The reddening maps of the SMC obtained from the analyses with/without breaks in the Leavitt law show good agreement with each other as well as with other maps available in the literature. The Cartesian coordinates of individual stars with respect to the galaxy plane are obtained using the information of equatorial coordinates (α, δ) as well as extinction-free distance measurements. Modelling the observed 3D distribution of the Cepheids as a triaxial ellipsoid, we obtain the geometrical and viewing angle parameters of the SMC. The weighted average yields the following values of parameters for the SMC: the geometrical axes ratios of 1.000 ± 0.001: 1.544 ± 0.002: 9.742 ± 0.030 and the viewing angle parameters having inclination angle i = 3${^{\circ}_{.}}$465 ± 0${^{\circ}_{.}}$030 with respect to the longest axis from the line of sight and position angle of line of nodes (major axis) θlon = 63${^{\circ}_{.}}$086 ± 0${^{\circ}_{.}}$117.

Research on the characteristics of driver visual behavior in highway extra-long tunnel

In order to study the driver visual behavior in highway extra-long tunnel section, the paper used Smart Eye Pro5.7 Eye Tracking System to record the driver’s eye movement data, analyzed eye movement index, such as pupil area, X sight angle, Y sight angle, percentage of fixation times, percentage of fixation time and mean fixation time. The results showed that the driver’s pupil area changes rapidly to adapt brightness variation in the entrance and exit of the tunnel. After entering the tunnel, the psychological state of drivers tends to be stable, and there is a tendency of gradual relaxation. Drivers are more focused and look down.

Influence of Angles of Shighting and the Earth's Surface Curvature on the Spatial Resolution of the Space Electro-Optical Viewing System

Background. One of the key differences between the aeronautical and space optical-electronic viewing systems (OEVS) of remote sensing of the Earth is the height from which the Earth's surface picture is taken. The difference between the heights of aircraft and spacecraft devises can reach several orders of magnitude, so if for aeronautical OEVS you can calculate spatial division on a plane, then for space OEVS this is critical and it is necessary to additionally consider the Earth's surface curvature, especially for angles of sighting other than zero.Objective. The aim of the paper is to develop physico-mathematical model for determining the resolution of the OEVS, which considers the Earth's surface curvature, the orbital height and location of the spacecraft position for different angles of shighting.Methods. In the basis of physical and mathematical model is proposed to use a biaxial ellipsoid as an approximation of the Earth shape to determine its surface curvature and Sun-synchronous orbit trajectory.Results. Practical results of the calculations prove that the Earth's surface curvature for space OEVS significantly influence the spatial resolution and differs from the results obtained by physical and mathematical model in which the spatial resolution is determined on a flat surface. The results of the design show, that when deflected at the angles of shighting, it is necessary to consider the additional deflection in calculations, which it increases, when distance increases for the nadir. At maximum angles of sight, pitch and roll to ±35º, i.e. when the OEVS is deflected at 44.7º from the nadir, the additional deflection is 6.3º, which significantly influences the determination of spatial resolution.Conclusions. The analysis of the proposed the physico-mathematical model of the OEVS showed that the Earth's surface curvature orbit trajectory and the location of the spacecraft, unlike the height, influence the pixels’ projection shape deformation. In this case, the values of the projection tilt angles of the rows and columns of the matrix detector relative to the flight direction change nonlinearly, which adversely influence the system modulation transfer function and require the calibration for some parameters during the flight depending on the angles of shighting and location coordinates.

Backstepping Sliding Mode Control for Radar Seeker Servo System Considering Guidance and Control System.

This paper investigates the design of a missile seeker servo system combined with a guidance and control system. Firstly, a complete model containing a missile seeker servo system, missile guidance system, and missile control system (SGCS) was creatively proposed. Secondly, a designed high-order tracking differentiator (HTD) was used to estimate states of systems in real time, which guarantees the feasibility of the designed algorithm. To guarantee tracking precision and robustness, backstepping sliding-mode control was adopted. Aiming at the main problem of projectile motion disturbance, an adaptive radial basis function neural network (RBFNN) was proposed to compensate for disturbance. Adaptive RBFNN especially achieves online adjustment of residual error, which promotes estimation precision and eliminates the “chattering phenomenon”. The boundedness of all signals, including estimation error of high-order tracking differentiator, was especially proved via the Lyapunov stability theory, which is more rigorous. Finally, in considered scenarios, line of sight angle (LOSA)-tracking simulations were carried out to verify the tracking performance, and a Monte Carlo miss-distance simulation is presented to validate the effectiveness of the proposed method.

A composite impact-time-control guidance law and simultaneous arrival

A new composite impact time control guidance law is proposed for simultaneous attack against a ground target. The guidance strategy is composed of two phases. Specifically, the first phase is to guide the missile to proper switching relative range for the second phase. After which, the second phase will lead the missile to the target with a desired impact time by using the proposed Lyapunov based guidance scheme. The impact time is given in a simple analytical form of initial states and switching relative range, the value of which is determined to control the impact time. The proper range of the switching state is analyzed considering the line of sight angle constraint. And the permissible range for impact time can be calculated corresponding to the proper switching state. Two classes of simultaneous attack are considered to demonstrate the effectiveness of the impact time control. One is the sequential launch, and the other is a salvo launch of multiple missiles from different positions. Numerical simulations are carried out to verify the performance of the proposed methodology.

Drivers’ effective decelerating zone in an urban Vehicle-Pedestrian conflict situation: Observational studies and analyses

To analyse the drivers’ decelerating behavior in conflict avoidance process under Vehicle-Pedestrian conflict situation is accordingly a surrogate method for the guidance of driver evasive manoeuvre and improving the active driving safety. Field observation data has been collected by video recording and image processing at urban unsignalized midblock crosswalks in Beijng, China and Munich, Germany. The relationship between deceleration rate and vehicle speed has been statistically described. By analyzing how the time-related measures (Vehicle Time to Conflict Point and Pedestrian Time to Conflict Point) and the distance-related measures (Vehicle longitudinal distance to Conflict Point and Pedestrian Lateral distance to Conflict Point) affect the deceleration rate choice, the drivers‘ effective decelerating zone with sight angle has been proposed with the consideration of longitudinal & lateral conflict behavior. Minimum Vehicle-Pedestrian conflict distance is calculated and a 2 m minimum distance is suggested as the threshold for collision discrimination. Comparisons which address the needs to make the intercultural adaptation when introducing Driver Assistance Systems to developing countries have also been made to show the significant differences between China and Germany. The whole work could hopefully be the groundwork in the target of conflict pre-scanning by decelerating zones under various conflict situations and the design of vehicle active safety systems.