Azimuth Correction Research Articles

Research on Aircraft Direction Finding Based on Antenna Directionality Parameter Identification

Radar direction finding is an essential cooperative monitoring method for aircraft, and the directional parameters of the direction-finding antenna determine the accuracy of direction finding. A modified amplitude comparison direction finding model is proposed based on the traditional principle of adjacent amplitude comparison direction finding and the error of amplitude comparison direction finding. Based on the modified amplitude comparison direction finding model, an error correction genetic simulated annealing (COR-GSA) algorithm is proposed to identify unknown directional antenna directionality parameters by determining the antenna directionality parameters that need to be identified. Identification experiments were conducted using a self-designed dual channel DF receiver, and 1000 sets of aircraft real azimuth data were used for verification. The results showed that using the COR-GSA algorithm to identify antenna directional parameters had the highest DF accuracy. Finally, the identified antenna directionality parameters were used to track the aircraft’s azimuth, and the tracking error was reduced by 18.3% compared to the tracking error without azimuth correction.

Azimuth correction for passive surface wave dispersion based on polarization analysis

SUMMARY Passive surface wave methods have found extensive application in near-surface investigation due to their benefits of low costs, non-invasiveness and high accuracy. Linear arrays are usually adopted in urban environments for their convenience and efficiency. However, the distribution of noise sources in densely populated urban areas varies rapidly in time and space, making it challenging to estimate accurate dispersion spectra using a linear array. To solve this problem, we propose a polarization analysis-based azimuthal correction method. We first obtain the azimuth of each segment by calculating the correlation coefficient of three-component ambient noise data. The normalized correlation coefficient is then applied for quality control to select reliable segments. For selected segments, the overestimated velocity caused by directional sources are corrected to obtain accurate dispersion spectra. A synthetic test is conducted to demonstrate the feasibility of our method. Compared with the dispersion spectra obtained without any correction, the dispersion spectra obtained following the suggested scheme are more consistent with the theoretical dispersion curves. Two real-world examples at crossroads show the superiority of the proposed technique in obtaining higher resolution dispersion energy and more accurate phase velocities. In addition, our approach can attenuate the artefacts and improve the dispersion measurements.

APO-ELM Model for Improving Azimuth Correction of Shipborne HFSWR

Shipborne high-frequency surface wave radar (HFSWR) has a wide range of applications and plays an important role in moving target detection and tracking. However, the complexity of the sea detection environment causes the target signals received by shipborne HFSWR to be seriously disturbed by sea clutter. Sea clutter increases the difficulty of azimuth estimation, resulting in a challenging problem for shipborne HFSWR. To solve this problem, a novel azimuth correction method based on adaptive boosting error feedback dynamic weighted particle swarm optimization extreme learning machine (APO-ELM) is proposed to improve the azimuth estimation accuracy of shipborne HFSWR. First, the sea clutter is modeled and simulated. Then, we study its characteristics and analyze the influence of its characteristics on the first-order clutter spectrum and target detection accuracy, respectively. In addition, the proposed improved particle swarm optimization (PSO) and adaptive neuron clipping algorithm are used to optimize the input parameters of the ELM network. Then, the network performs error feedback based on the optimized parameter performance and updates the feature matrix, which can give a minimum clutter-error estimation. After that, it iteratively trains multiple weak learners using the adaptive boosting (AdaBoost) algorithm to form a strong learner and make strong predictions. Finally, after error compensation, the best azimuth estimation results are obtained. The sample sets used for the APO-ELM network are obtained from field shipborne HFSWR data. The network training and testing features include the wind direction, sea current, wind speed, platform speed, and signal-to-clutter ratio (SCR). The experimental results show that this method has a lower root-mean-square error than the back-propagation neural network and support vector regression (SVR) azimuth correction methods, which verifies the effectiveness of the proposed method.

Contributions to Unsupervised Online Misalignment Detection and Bumper Error Compensation for Automotive Radar.

One of the fundamental sensors utilized in the Advanced Driver Assist System (ADAS) is the radar sensor. Automotive-related functions need highly precise detection and range of traffic and surroundings; otherwise, the whole ADAS performance suffers. The radar placement beneath a bumper or a cover, the age or exposure to accidents or vehicle vibration, vehicle integration, and mounting tolerances will impact the angular performance of the radar sensor. In this research, we present an unsupervised online method for elevation mounting angle error compensation and a method for bumper and environmental error compensation in the azimuth direction. The proposed methods need no specific calibration jig and may be used to replace traditional initial calibration methods; they also enable ongoing calibration throughout the sensor's lifespan. A first proposed standalone method for vertical alignment uses stationary radar targets reflected from the environment to calculate a vertical misalignment angle with a line-fitting algorithm. The vertical mounting error compensation approach delivers two types of correction values: a dynamic value that converges quickly in the case of minor accidents and a more stable correction value that converges slowly but offers a long-term compensation value over the sensor's lifespan. A second proposed solution uses the vehicle velocity and radar targets properties, like relative velocity and measured azimuth angle, to calculate an individual azimuth correction curve. Real-world data collected from drive testing with a 77 GHz series automobile radar was used to analyze the performance of the proposed methods, yielding encouraging results.

Airglow Observation and Statistical Analysis of Plasma Bubbles over China

Airglow observation is a very effective method to investigate plasma bubbles, and can obtain their horizontal structure. In this study, the image processing method was used to process airglow data, including image enhancement, azimuth correction, and image projection, and the clear image products of equatorial plasma bubbles (EPBs) were obtained. Based on the optical data of the airglow imager in Hainan, we investigated the main optical features of EPBs, and statistically analyzed the occurrence of EPBs from September 2014 to August 2015. The observation results show that EPB exhibits plume-shaped structures, usually tilting westward, and EPB extends to a long distance along the geomagnetic field lines. It is found that the west wall of EPB is relatively stable, while there are some bifurcations on the east wall of EPB, and the bifurcation of EPB becomes more pronounced with time. Moreover, the spatial scale of EPB gradually increases with time, which is about several hundred kilometers, and the drift velocity of EPB is in the range of 40–130 m/s (+/−20 m/s). The statistical results show that EPBs mainly occur in the months of September to November and February to April, with a higher occurrence rate. In terms of seasonal occurrence, EPBs tend to appear more frequently in spring and autumn, and the occurrence rate of EPBs is relatively low in winter and summer.

Azimuth and Origin Correction Method for Improving Radar Measurement Accuracy

Azimuth and Origin Correction Method for Improving Radar Measurement Accuracy

Correction of the Solar Azimuth Discontinuity at Sunrise and Sunset

Solar azimuth may become indefinite at sunrise and sunset. This discrepancy is corrected in the present work. The correction concerns application of Fourier–series analysis to the solar paths over a site during days when the problem arises. The result is the derivation of a new curve that is fitted with great accuracy to the daily solar azimuth values, thus bridging the gap of the discontinuity. A demonstration for the solar azimuth correction is given for 3 sites around the world (Athens, Stockholm, and Sydney). The correction can be applied to any solar geometry code; in this work the algorithm of the XRONOS code is selected without (XRONOS.bas, a BASIC programme) and with (XRONOS.m, a MATLAB code) the correction proposed. A corrected expression for the atmospheric refractive index at various altitudes is given in Appendix A as the refraction of solar right is treated in XRONOS.

Considerations on envelope design criteria for hybrid ventilation thermal management of school buildings in hot–humid climates

Owing to the impact of global warming, the weather becomes hotter than the past. Responding to the hot–humid climate, the Taiwan government intends to install air-conditioning in classrooms to provide comfort study environment. The thermal management of school buildings is separated into naturally ventilated and air-conditioning seasons based on the strategies of reducing energy use while maintaining thermal comfort. In this paper, the school buildings located in northern and southern Taiwan (Taipei and Kaohsiung) are selected as study objectives to simulate cooling load, thermal comfort, and the natural ventilation potential to discuss the parameters related to building envelope design. Through regression analysis of the 360 simulation cases, the Overall Thermal Transfer Value (OTTV) for Taipei and Kaohsiung are established. Besides, the coefficient of azimuth correction factor and area ratio correction factor are clarified for equivalent ventilation area. Through coupled analysis, the Pareto ranking method is used to obtain numerical solution sets corresponding to the index including OTTV and equivalent ventilation area.Consequently, a school building envelope design criteria for balancing the energy use and thermal comfort is proposed. According to the analysis results and the intersection of OTTV and equivalent ventilation area at Pareto front, it is confirmed that the restriction of the OTTV index is 20 W/m2 in Taipei and Kaohsiung; the equivalent ventilation area which guarantees no overheating risk during natural ventilation season is determined as 9.5 m2 in Taipei and 14.3 m2 in Kaohsiung. Furthermore, the influence level of the parameters is clarified that the area and shading performance of windows make a major influence on sensible cooling load; comparing to external shading, the window insulation performance is considerably less important. Overall, this study seeks the balance between energy use and thermal comfort then provide the efficient strategies at the initial design stage through the proposed criteria.

A transfer alignment method for inertial attitude correction of spherical motor on moving base

Inertial attitude measurement of spherical motor on moving base (SMMB) confronts the problems of unobservable azimuth and acceleration interference. This paper presents a transfer alignment method for inertial attitude correction of SMMB with specific exterior excitation. Because of the low friction torque of the spherical joint in the SMMB, the rotation is not able to be wholly transferred from base to rotor, which is required in the common method of velocity-attitude matching. With an explicit model about the acceleration transfer, the accumulation of unobservable error based on nominal-state is derived. Then the transfer alignment algorithm with innovation-based adaptive filter is proposed. The method brings external acceleration measurement into regular attitude estimation and adopts both estimation of unobservable error and acceleration transfer error into adaptive filter for the balance of azimuth correction and tilt error suppression. The simulation and analysis show that the method can correct the unobservable azimuth angle in high amplitude and frequency excitation as well as better tilt error suppression for transfer error with 20% uncertainty. The method is verified in a prototype platform.

Azimuth correction system of an inclinometer

The paper is devoted to azimuth correction system of an inclinometer used for well drilling in high latitude areas. In these areas, ordinary types of navigation equipment (gyroscopic and magnetic sensors) are ineffective because of small horizontal component of the Earth rotation velocity and significant values of magnetic declination. In the paper, an approach to the correction system study is described. The system consisting of two vibrational sources shifted from the wellhead to a certain distance in the direction of projected drilling and spaced to same distance from the specified direction is characterized.Special attention is given to investigation of a motion model of a flexible shaft, which is proposed as the vibrational source of the system. On the basis of experiments and calculations, it is shown in the paper that in a complex mechanical system with a flexible shaft of vibrational source, a consistent multi-resonant effect can be observed when the shaft starts rotating. Moreover, a simulation model and results of estimation of the vibrational source power are presented. A possibility of use a compact “handheld” vibrational source with flexible shaft for azimuth correction system operation is shown

Optical observation of plasma bubbles and comparative study of multiple methods of observing the ionosphere over China

Ionospheric plasma bubbles and scintillation phenomena often occur at low latitudes in China. The all-sky airglow imager located at Fuke station in Hainan (19.5°N, 109.2°E) is part of the Meridian project in China. In this work, we used mainly the observation data obtained by the imager and a digisonde to study plasma bubbles. Optical image processing—including image enhancement, azimuth correction and image projection—was performed on the original airglow observation images, and clear high-resolution images of the bubbles were obtained. Based on these, the morphological features, spatial and temporal variations, spatial scale, drift velocity of the plasma bubbles in the F region of the ionosphere were investigated and analyzed. The plasma bubbles appeared as long, dark stripes on the bright airglow emission background. Their large-scale structures often bifurcated vertically, and were usually tilted westward with north-south extension along the magnetic field lines. The east-west scale of the plasma bubbles was usually greater than 200 km and these increased gradually with time. Moreover, the distance between the adjacent plasma bubbles also increased over time, and was in the 100–400 km range. Plasma bubbles generally drifted eastward with an average drift velocity of approximately 90 m/s. The occurrence and duration of the plasma bubbles were compared with digisonde observations, and it was shown that plasma bubbles lasted for nearly four hours. Additionally, the main characteristics of the plasma bubbles were obtained using both optical and radio observations and the study of which can be beneficial for monitoring and predicting ionospheric scintillations.

Fuzzy Controller for Autonomous Vehicle Based on Rough Sets

This article presents a fuzzy controller for autonomous vehicle to intelligently recognize running environment and avoid an obstacle, which is constructed by rough sets (RSs) and an adaptive neuro-fuzzy inference system (ANFIS). Firstly, RSs are considered to propose a pyramid normalization (PN) method for normalizing state parameters (SPs) which are defined to recognize relative position such as distance and angle among a vehicle, an obstacle and target pathway, to improve the adaptability of complex environment and optimize the database of driving knowledge. Secondly, ANFIS is employed to design a controller with self-position azimuth correction (SPAC) for performing trajectory tracking and obstacle avoidance. Finally, the proposed methods have been implemented on the model vehicle called “RoboCar”, and compared with various fuzzy control approaches such as the initial SPs with ANFIS, the normalized SPs with fuzzy neural network (FNN), and the initial SPs with FNN. Time, maximum tracking error and mean tracking error are calculated to evaluate the performance. The experimental results with four kinds of target pathways have shown that the PN-ANFIS-based controller has saved time (7.6%), reduced maximum tracking error (8.1%) and mean tracking error (8.5%).

Determining glacier flow direction from till fabrics

Field and experimental data indicate that fabrics of sheared basal tills, based on particle orientations and on anisotropy of magnetic susceptibility, are inclined relative to the macroscopic plane of shear. As a result, if this plane is tilted with a transverse component, one of the longest-standing axioms of glacial geology—that particles in basal till are preferentially oriented parallel to the direction of shear—is not strictly true. The resultant correction to the shearing direction increases with the transverse and longitudinal components of shear-plane inclination and with the magnitude of the fabric inclination relative to the shear plane. Azimuthal corrections calculated herein range from being negligible to a few tens of degrees for reasonable ranges of shear-plane tilt. The past success of fabric azimuths as indicators of flow direction, despite the absence of this correction, likely reflects the clustering of shear planes about the horizontal in basal tills. However, on the flanks of accreting subglacial bedforms, shear-plane attitudes may well conform to the local bedform slope. As illustrated with hypothetical fabrics of drumlins and flutes, azimuthal corrections can in that case be sufficiently large and systematic to seriously affect interpretations of bedform genesis.

Azimuth correction of optoelectronic mast based on EO calibrated INS

Azimuth correction of optoelectronic mast based on EO calibrated INS

Note: Vectorial-magneto optical Kerr effect technique combined with variable temperature and full angular range all in a single setup.

Here, we report on a versatile full angular resolved/broad temperature range/vectorial magneto optical Kerr effect (MOKE) magnetometer, named TRISTAN. Its versatility relies on its capacity to probe temperature and angular dependencies of magnetization reversal processes without the need to do any intervention on the apparatus during measurements. The setup is a combination of a vectorial MOKE bench and a cryostat with optical access. The cryostat has a motorized rotatable sample holder with azimuthal correction. It allows for simultaneous and quantitative acquisition of the two in-plane magnetization components during the hysteresis loop at different temperatures from 4 K up to 500 K and in the whole angular range, without neither changing magnet orientation nor opening the cryostat. Measurements performed in a model system with competing collinear biaxial and uniaxial contributions are presented to illustrate its capabilities.

특수목적을 위한 이동형 영상 터미널 장비의 추적안테나 시스템에 적용하기 위한 방위각보정 알고리즘 구현

In this paper, we proposed on the azimuth correction method for a line-of-sight data-link tracking antenna system. Tracking antenna system is essential to maintain line-of-sight between moving object and data-link equipment. In order to calculate the azimuth and elevation between the moving object and antenna system, we used GPS data. also to match the each coordinate systems, we used geomagnetic sensor or beacon. However, the geomagnetic disturbance-prone terrain in places difficult to correct calibration. The first step, finds the location of the strongest RF signal, we should remember the difference between the reference point and the detected position of the antenna. The second step, we could communicate each other. And the azimuth angle is calculated by GPS values. Despite the geomagnetic interference, we can correct the azimuth angle quickly and easily.

Taking into account nonholonomic contraints of SINS output signals in azimuth correction algorithms

Modern strapdown inertial navigation systems (SINS) usually calculate the course angle of aircraft as a sum of two angles: the azimuth angle of the ‘platform’ and the heading determined by a gyro. The values of each of these two angles depend on the initial conditions of the azimuth channel alignment and the flight path of the aircraft at the previous phases of the flight. The paper studies this ambiguity; a method is proposed to take it into account in the algorithms for correction of the SINS heading channel.

Topographic, spectral and thermal inertia analysis of interior layered deposits in Iani Chaos, Mars

We present an analysis of Interior Layered Deposits (ILDs) in Iani Chaos using visible, infrared, hyperspectral and topographic datasets acquired by instruments aboard NASA’s Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and ESA’s Mars Express spacecraft. We focus on four main regions where ILDs outcrop in Iani Chaos. Deposits span a ∼2km range of elevations and exhibit moderate to high albedos, layering at sub-decameter scales, thermal inertias of 300–800Jm−2K−1s−1/2 and a range of surface textures. Thermal inertia calculations use slope and azimuth corrections from High Resolution Stereo Camera (HRSC) topography. Spectral features in hyperspectral data acquired by NASA’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) suggest that gypsum (CaSO4·2H2O) and kieserite (MgSO4·H2O) are present in most deposits. We report absorptions typically exhibited by alunite (KAl3(SO4)2(OH)6) and jarosite KFe33+(OH)6(SO4)2 as well as a number of features that may be attributable to a wide range of mono- and polyhydrated sulphates and hydroxyl-sulphates bearing a number of cations, including Mg2+, Fe2+, Fe3+ and Ca2+. Spectral features similar to those of ammonium sulphates may also be present.Analysis of a HiRISE stereo DEM shows planar layering in some ILDs, favouring a sedimentary deposition origin. Stratigraphic mapping of hydration and sulphate spectral features in flat ILDs in central Iani Chaos suggest that specific elevation intervals in the stratigraphic column were subject to different levels of hydration, perhaps during episodes of water table elevation. This is consistent with formation models for ILDs and hydrological modelling. Geomorphic characteristics of deposits in northern and southern Iani Chaos suggest their relatively recent exhumation and significant erosion by aeolian processes. We conclude that any formation theory for ILDs in Iani Chaos should support mechanisms for different hydration states at different stratigraphic elevations and subsequent significant aeolian erosion, burial and re-exposure.

Relative INS/GNSS aerial control in integrated sensor orientation: Models and performance

In this paper we present the models and discuss the performance of relative position and attitude INS/GNSS aerial control observations in integrated sensor orientation. In relative aerial control, we use the relative position and attitude of the IMU at the exposure times of successive images instead of the usual absolute position and attitude for each image. With relative aerial control, the GNSS shift correction parameters and the IMU-to-camera boresight matrix vanish from the functional models and so does the problem of their selection. The presented models are formulated with the usual original INS/GNSS attitude parameterisation (heading, pitch and roll) to avoid unnecessary and error-prone intermediate re-parameterisation steps. Furthermore, we present a rigorous model formulation, for both aerial control and photogrammetric observations, in local mapping coordinate systems that eliminate the need of the so-called height and azimuth corrections and that guarantee geodetic correctness and consistency. The overall resulting modelling scheme allows for a direct incorporation of INS/GNSS aerial control observations into the integrated sensor orientation processing chain in a simple and robust way. The performance of the new models is evaluated with three independent data sets and the results show a comparable to better performance.

Slowness–azimuth corrections of teleseismic events for IMS primary arrays in China

The seismic arrays at Hailar (HILR) and at Lanzhou (LZDM) in China are both primary stations of the International Monitoring System for verifying compliance with the Comprehensive Nuclear Test Ban Treaty. These two stations became operational in 2002 and have since then provided continuous data. In this study, the so-called slowness–azimuth station corrections (SASC) were derived and used to improve the location accuracy of the two arrays. The SASC are found by comparing the back-azimuth and slownesses obtained from array processing to the theoretical values calculated from the reported event locations and the corresponding seismic velocity model. Events reported by the National Earthquake International Center in the time period 2002 to 2006 were used as reference events, and the IASP91 was used as the theoretical velocity model. Small correction vectors with random orientation were found for HILR. Larger correction vectors with systematic vector biases were found for LZDM. The LZDM correction vectors seem to point to the same direction in a large part of the slowness space and may be attributed to local structure. After introducing the SASC for HILR, the standard deviations of back-azimuth and slowness residuals drop from 7.1° to 4.6° and from 1.0 to 0.6 s/°, respectively. For LZDM, these values drop from 22.3° to 10.2° and from 2.9 to 1.1 s/°, respectively. The variations of back-azimuth and slowness residuals were reduced by 32% and 30.2%, respectively, for HILR after SASC and the reductions were 21% and 40.2% for LZDM. The improvements were 77% in back-azimuth and 67% in slowness location for HILR and were 79% and 81% for LZDM after SASC.