Elevation Axis Research Articles

3D Indoor Mapping System Using 2D LiDAR Sensor for Drones

Most 3D scanners are heavy, bulky and costly. These are the major factors that make them irrelevant to be attached to a drone for autonomous navigation. With modern technologies, it is possible to design a simple 3D scanner for autonomous navigation. The objective of this study is to design a cost effective 3D indoor mapping system using a 2D light detection and ranging (LiDAR) sensor for a drone. This simple 3D scanner is realised using a LiDAR sensor together with two servo motors to create the azimuth and elevation axes. An Arduino Uno is used as the interface between the scanner and computer for the real-time communication via serial port. In addition, an open source Point-Cloud Tool software is used to test and view the 3D scanner data. To study the accuracy and efficiency of the system, the LiDAR sensor data from the scanner is obtained in real-time in point-cloud form. The experimental results proved that the proposed system can perform the 2D and 3D scans with tolerable performance. Â

Functional estimation of bony segment lengths using magneto-inertial sensing: Application to the humerus.

Inertial sensor technology has assumed an increasingly important role in the field of human motion analysis. However, the reliability of the kinematic estimates could still be critical for specific applications in the field of functional evaluation and motor rehabilitation. Within this context, the definition of subject-specific multi-body kinematic models is crucial since it affects the accuracy and repeatability of movement reconstruction. A key step for kinematic model calibration is the determination of bony segment lengths. This study proposes a functional approach for the in vivo estimation of the humerus length using a single magneto-inertial measurement unit (MIMU) positioned on the right distal posterior forearm. The humerus length was estimated as the distance between the shoulder elevation axis and the elbow flexion–extension axis. The calibration exercise involved five shoulder elevations in the sagittal plane with the elbow completely extended and five elbow flexion–extensions with the upper arm rigidly aligned to the trunk. Validation of the method was conducted on five healthy subjects using the humerus length computed from magnetic resonance imaging as the gold standard. The method showed mean absolute errors of 12 ± 9 mm, which were in the estimate of the humerus length. When using magneto-inertial technology, the proposed functional method represents a promising alternative to the regressive methods or manual measurements for performing kinematic model calibrations. Although the proposed methodology was validated for the estimation of the humerus length, the same approach can be potentially extended to other body segments.

Electro mechanical linear actuator using roller screws

Electro Mechanical linear Actuators as the name suggests are linear actuators operated by electric motor. The linear motion is desirable to drive a high inertia weapon system in elevation axis. In this paper, design and development aspects of an Electromechanical linear actuator using Roller screw has been attempted. Initial Comparison with ball screw drive suggests that roller screws are favorable for high dynamic load application. Selection and functional parameters of roller screw had been evaluated to optimize the linear actuator based on roller screw. This paper studies in detail the design aspects of an electromechanical linear actuator. The variation of different parameters with respect to Lead of the roller screw has been studied.

Antipodal Vivaldi Antenna for Passive Imaging Technology in Ka Frequency Band

Passive Millimeterwave Imaging (PMI) Technology is used to view scene in foggy air conditions or to see concealed weapon under clothes that cannot be seen other technology because of the materials of weapon. There are some frequency windows to work with millimeterwave technology as 35, 96 and 220 GHz and it is near 35 GHz frequency for this work. Antenna is one of the most important part in PMI Technology, consequently; major importance has been given to this segment. Antipodal Vivaldi Antenna has 50.07 ohm input impedance for matching to the forward circuit, and -39.23 dB input reflection coefficient, S11, and 6.82 dB gain, is designed for 35.18 GHz in Computer Simulation Technology Studio Suite Program (CST). After the antenna is connected to the other circuits such as amplifier or detector, the created system will be integrated into a scanner which is capable of scanning azimuth and elevation axes. As a result, PMI System will be formed and ready to view the scene or the hidden things in haze air conditions.

Design, manufacture and performance analysis of an automatic antenna tracker for an unmanned aerial vehicle (UAV)

In conducting a disaster monitoring mission, an unmanned aerial vehicle (UAV) has to travel a long distance to cover the region that is hited by a disaster. In the monitoring mission, Air Data and Attitude Heading Reference System (ADAHRS) data are very important to always be displayed on the ground control station (GCS). Unfortunately, the area of monitoring mission is very wide, whereas the usage of an omnidirectional antenna in the disaster monitoring mission is limited to the UAV maximum range. Therefore, a high gain directional antenna is needed. However, the directional antenna has a disadvantage of always being directed to the target. To solve this problem, antenna tracker is made to track the UAV continuously so that the directional antenna can always be directed to the flying UAV. An antenna tracker using a 32-bit microcontroller and GPS with two degrees-of-freedom was developed. It is able to move 360 degrees on azimuth axis (yaw) and 90 degrees on elevation axis (pitch). Meanwhile, the directional antenna is three elements yagi type with a radiation capability of 6 dBi. By using the antenna tracker, larger UAV range was obtained and the connection between the UAV and the GCS could always be maintained with a minimum fluctuation of RSSI signal, compared to those without using antenna tracker.

Structural controls on distribution of dolines on Mount Anamas (Taurus Mountains, Turkey)

Solution dolines are characteristic landforms on the high plateaus of the Taurus Mountains. In this study, the effects of tectonic structures, drainage and slope conditions on the distribution and morphometric properties of dolines in the western part of the Central Taurus are explained. To delimit the dolines, 1/25000 scale topographic maps were used. The uppermost closed contour lines were digitized as polygons and the elevation, long and short axes, elongation ratios, orientation angles of the polygons were calculated. The doline density is compared with drainage density and mean slope values. A total of 111 rose diagrams were created in order to illustrate the superficial distribution of orientation. As a result, a total of 10,652 dolines were detected in a 711 km2 doline area and maximum density reaches 123 dolines/km2. However, according to the doline density, two distinct regions were detected, high density (R1) and low density (R2). Correlations between drainage density, slope angle and doline density are negative in the two regions. According to negative correlations, the drainage density is not a determinant factor in R1, while it is a determinant factor in R2. A 30° slope angle (in km2) limits doline distribution on the plateau surface.The orientation of all doline long axes is NW-SE, which is parallel to the general orographic extent of Mount Anamas. However, different orientations were detected and these orientations were showed in farther sub-regions according to the 111 gridded rose diagrams. The overall result of this study is that the fault and joint systems that developed on the thick-bedded limestone between thrust faults affected the doline density, while lateral strike-slip, normal faults and joint systems in front of the thrust belt were more effective on the geometric shapes of dolines.

FAST in Space: Considerations for a Multibeam, Multipurpose Survey Using China's 500-m Aperture Spherical Radio Telescope (FAST)

Having achieved 'first-light' right before the opening ceremony on September 25, 2016, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) is being busily commissioned. Its innovative design requires ~1000 points to be measured and driven instead of just the two axes of motion, e.g. Azimuth and Elevation for most of the conventional antennae, to realize pointing and tracking. We have devised a survey plan to utilized the full sensitivity of FAST, while minimizing the complexities in operation the system. The 19-beam L band focal plan array will be rotated to specific angles and taking continuous data streams while the surface shape and the focal cabin stay fixed. Such a survey will cover the northern sky in about 220 full days. Our aim is to obtain data for pulsar search, HI (neutral hydrogen) galaxies, HI imaging, and radio transients, simultaneously, through multiple backends. These data sets could be a significant contribution to all related fields in radio astronomy and remain relevant for decades.

Improving pointing of Toru\u0144 32-m radio telescope: effects of rail surface irregularities

Over the last few years a number of software and hardware improvements have been implemented to the 32-m Cassegrain radio telescope located near Toruń. The 19-bit angle encoders have been upgraded to 29-bit in azimuth and elevation axes. The control system has been substantially improved, in order to account for a number of previously-neglected, astrometric effects that are relevant for milli-degree pointing. In the summer 2015, as a result of maintenance works, the orientation of the secondary mirror has been slightly altered, which resulted in worsening of the pointing precision, much below the nominal telescope capabilities. In preparation for observations at the highest available frequency of 30-GHz, we use One Centimeter Receiver Array (OCRA), to take the most accurate pointing data ever collected with the telescope, and we analyze it in order to improve the pointing precision. We introduce a new generalized pointing model that, for the first time, accounts for the rail irregularities, and we show that the telescope can have root mean square pointing accuracy at the level < 8″ and < 12″ in azimuth and elevation respectively. Finally, we discuss the implemented pointing improvements in the light of effects that may influence their long-term stability.

Study on simulation and experiment of control for multiple launch rocket system by computed torque method

Poor dispersion characteristics of rockets, due to the orientation of the launcher for multiple launch rocket system (MLRS) departing from that intended, have always restricted the MLRS development for several decades. Orienting control is a key technique to improve the dispersion characteristics of rockets. The purpose of this paper is to propose an orienting control method for launcher of the MLRS in a salvo firing. Because the MLRS is a typical nonlinear system, the major difficulty in designing the orienting controller lies in the nonlinearity. To deal with the nonlinearity, the concept of computed torque control is introduced. The MLRS equation of motion is established using Lagrange method. The inner loop feedforward and the outer loop feedback are adopted to design the controllers for the azimuth and elevation axes of MLRS. By combining the inner and outer control loops together, the PID-computed torque controller is designed. The numerical simulation is implemented to show the control performance, and then, the effectiveness and applicability of the proposed controller are demonstrated by the firing experiment of a salvo of three rockets.

Design and Construction of Prototype Mobile Sun-Tracking System for Concentrator Photovoltaic System

This paper proposes a mobile sun-tracking system, which allows continuous tracking of the sun and effective harvesting of solar energy on mobile platforms. Based on the dynamic sun-tracking algorithm which we previously proposed, the system takes not only the date, time, and geographical information, but also the dynamic changes of coordinates of the mobile platforms into account to calculate the hour angle of sun relative to the ideal azimuth elevation axes in real time. The advantage of this design is that it can be easily duplicated for mass deployment on the land or ocean. Our results show that the accuracy of mobile tracking in stationary state is 8.085 mrad while the accuracy in mobile state is 127 mrad on average.

Sun Tracking Based on Hybrid Control with High Accuracy and Low Consumption

The concentrator photovoltaic (CPV) system needs a dual-axis sun tracking system with high precision to track the sun position. This is because the power generated by small solar multijunction cells with concentrators lens drops dramatically once the pointing angle position error exceeds maximum acceptance angle of less than 1°. In this present paper, a sun tracking unit based on optimized Hybrid control has been realized to improve the tracking accuracy and reactivity of a dual-axis tracking unit in CPV systems. The hybrid control system including two strategies based on closed-loop algorithm to communicate with LDRs sensors as well as an open loop algorithm based on astronomical equations is implemented and tested. The circuit of the hardware part related to the hybrid sun tracker has been carefully designed in such way the sun tracking continues along azimuth axis and the elevation axis in both clear and cloudy sky throughout the day. We first report the results of experimental analyses and comparison of tracking accuracy between the closed and open loop. Based on these results, the strategy of hybrid solution is proposed and implemented. The results of drivers consumption of the developed hybrid solar tracker indicate a low power consumption with a total energy of 3.66Wh along altitude axis and 3.03Wh along azimuth axis in the day. The tracking accuracy of hybrid control is less than ±0.4° along the two axes.

Influence of climatic and geographic factors on the spatial distribution of Qinghai spruce forests in the dryland Qilian Mountains of Northwest China

The effect of climate variables (temperature and precipitation) on forest spatial distribution is more prominent in dryland high mountains, where forest distribution is inherently very sensitive to and strongly limited by the substantial spatial heterogeneity of site conditions. Thus, a more reliable prediction of forest distribution under changing environment depends upon an understanding of the joint influence of climatic and topographic factors and their thresholds. This study was conducted on Qinghai spruce forests as dominant tree species in the Qilian Mountains of northwest China. The spruce forest distribution was surveyed by remote sensing in Dayekou watershed and by field investigation in a nested smaller watershed. Analyses showed that mean annual air temperature and precipitation, which vary with elevation, are the key climatic factors determining forest distribution, but slope aspect also plays an essential role. The potential core distribution area of denser forests and potential distribution area including sparse forests are between the axes of elevation (2635.5–3302.5 and 2603.4–3325.8m a.s.l.) and slope aspect (−74.4–61.2° and −162.6–147.1° deviated from north). The corresponding threshold of mean annual air temperature at the upper elevation boundary is −2.59 and −2.73°C, while the threshold of mean annual precipitation at the lower elevation boundary is 378.1 and 372.3 mm, respectively. Using these thresholds and the elevation gradients of climatic factors, the shifting of elevation boundaries under climate change scenarios can be predicted. However, the forest distribution is also limited by a soil thickness of ≥40cm; and by slope position of lower-, lower- and middle-, and entire-slope within the elevation ranges of <2800, 2800–2900, and >2900m a.s.l., respectively. This study showed that adding geographic factors will greatly improve the prediction of changes in forest distribution area in dryland mountains, in addition to the influence of climatic factors.

Spatial distribution of Qinghai spruce forests and the thresholds of influencing factors in a small catchment, Qilian Mountains, northwest China

Forest restoration in dryland mountainous areas is extremely difficult due to dry climate, complex topography and accelerating climate change. Thus, exact identification of suitable sites is required. This study at a small watershed of Qilian Mountains, Northwest China, aimed to determine the important factors and their thresholds limiting the spatial distribution of forests of Qinghai spruce (Picea crassifolia), a locally dominant tree species. The watershed was divided into 342 spatial units. Their location, terrain and vegetation characteristics were recorded. Statistical analysis showed that the potential distribution area of Qinghai spruce forests is within an ellipse with the axes of elevation (from 2673.6 to 3202.2 m a.s.l.) and slope aspect (from −162.1° to 75.1° deviated from North). Within this ellipse, the forested sites have a soil thickness ≥40 cm, and slope positions of lower-slope, lower- or middle-slope, anywhere if the elevation is <2800, 2800–2900, >2900 m a.s.l, respectively. The corresponding mean annual air temperature at upper elevation boundary is −2.69 °C, while the mean annual precipitation at lower elevation boundary is 374 (331) mm within the small watershed (study area). The high prediction accuracy using these 4 factors can help to identify suitable sites and increase the success of afforestation.

Basic study on ultrasonic monitoring using 1.5-dimensional ultrasound phased array for ultrasound-guided high-intensity focused ultrasound treatment

We have been studying a real-time detection method for tissue changes induced by high-intensity focused ultrasound (HIFU) treatment using ultrasonic RF signals. It has been difficult to track the target region when the tissue to be treated deviates from the imaging plane along the elevation axis of the probe. In this study, a new 1.5-dimensional (1.5D) prototype phased array probe consisting of transducer elements along both the lateral and elevation axes was developed to track tissue motion along the elevation axis of the probe, and the elevational displacement range where the tracking is effective was investigated. The complex cross-correlation coefficient based on a block matching algorithm was applied to 2.5D volumetric RF images acquired by the 1.5D probe and the displacement vector along the elevation axis was calculated. From the results, it was found that the effective tracking range using this prototype probe was up to 3 mm, about 3 times that of a conventional 1D imaging probe. The proposed 1.5D phased array probe has the potential to track target tissue with intrafractional motion.

System Identification &amp; Modelling of GMRT (Giant Meter Wave Radio Telescope)

AbstractGMRT is a unique Indian facility for radio astronomical research to support precision tracking of celestial objects. Currently a type II position servo at GMRT provides ∼1 arc min tracking accuracy. The tracking accuracy deteriorates in the presence of wind gusts. To improve the tracking accuracy, it is proposed to upgrade GMRT servo system with modern high performance controllers, e.g., a Linear Quadratic Gaussian (LQG) controller. However, in order to design a LQG controller, accurate telescope model is required which can be obtained through an experimental approach based on response measurements (System Identification). This paper presents the experimental setup, test conditions and results of system identification experiments carried out for the Elevation axis of one of the telescopes of GMRT. The model was then validated through simulation experiments. The response of the identified system closely matches that of the physical telescope, setting the stage for designing an optimum controller for GMRT.

Acceleration feedback of a current-following synchronized control algorithm for telescope elevation axis

This paper proposes a dual-motor configuration to enhance closed-loop performance of a telescope control system. Two identical motors are mounted on each side of a U-type frame to drive the telescope elevation axis instead of a single motor drive, which is usually used in a classical design. This new configuration and mechanism can reduce the motor to half the size used in the former design, and it also provides some other advantages. A master-slave current control mode is employed to synchronize the two motors. Acceleration feedback control is utilized to further enhance the servo performance. Extensive experiments are used to validate the effectiveness of the proposed control algorithm in synchronization, disturbance attenuation and low-velocity tracking.

Stabilization of the Two-Axis Gimbal System Based on an Adaptive Fractional-Order Sliding-Mode Controller

ABSTRACTThis paper introduces an adaptive fractional-order sliding-mode controller for stabilization of a two-axis gimbal platform in the presence of the torque disturbance effects. To tend the angular velocities of the inner gimbal in the elevation and azimuth axes to zero, an adaptive fractional-order sliding-mode approach is utilized. To achieve this goal, fractional-order sliding surfaces in both azimuth and elevation axes and the corresponding adaptive controllers with adjustable parameters tuned according to Lyapunov-based adaptation mechanisms are employed. The optimal value of the fractional order is obtained through an integral square error performance index minimization. The moments products uncertainties are incorporated in the design procedure. The numerical simulations demonstrate that the proposed control approach is robust against the moments products variations.

Volume Height Estimation based on Fusion of Discrete Fourier Transform (DFT) and Least Square (LS) in a Tomographic SAR Application

Tomographic-SAR (Synthetic Aperture Radar) is a 3D Radar imaging technique, based on spectral estimation tools. This technique is used to estimate the distribution of the backscattering signal in the elevation axis, for each azimuth-range resolution cell of the SAR image. Spectral estimation algorithms belong to two families, non parametric estimation algorithms which include DFT (Discrete Fourier Transform), SVD (Single Value Decomposition), MUSIC (Multiple Signal Classification), CAPON and parametric estimation algorithms such as LS (Least Square) and ESPRIT (Estimation of signal parameters via rotation invariance techniques). In this paper we present an inversion algorithm based on the fusion of DFT and LS for the estimation of the reflectivity signal along the elevation axis. With an appropriate combination of these two algorithms and a realistic modeling of the signal distribution, we obtain a high resolution estimate of the reflectivity signal with medium computational effort. The inversion algorithm is tested on a forested area (Vasterbotten in northern Sweden), with multibaseline data set acquired in L-band (BioSAR-2008 project). Results are promising with the proposed algorithm. We used MUSIC and RVoG (Random Volume over Ground) inversions for comparison and LIDAR (Laser Imaging Detection And Ranging) image as datasets for validation of the results.

Tahtalı Dağları (Orta Toroslar) karst platosu üzerinde dolin ve uvala gelişiminin CBS tabanlı analizi

Dolines and uvalas which are characteristic landform of karstic areas displays intensive development in Taurus Karstic Zone In this study, dolines and uvalas on karstic plateau located at southwest of Tahtali Mountains (Central Taurus), on borderline between Kayseri-Adana were investigated. Totally 992 karstic dissolution pits including 846 dolines and 146 uvalas have been identified on karstic plateau as result of investigation of 1/25000 scale topographic map. Center X and Y coordinates, elevation (m), area (m2), perimeter (m), long and short axis length (m), azimuth of long axis (o), ratio of long axis to short axis, density, circularity and nearest neighbor index values of each pit are calculated by GIS. By examining relationships among obtained data, factors controlling development of doline and uvalas were attempted to reveal. Most of the forms are found on Upper Cretase limestone at between 2200 to 2350 meters. Areas of the forms vary between 16 m2 - 230000 m2, while their maximum length changes between 192 - 816 meters. Mean density of the forms is 22 pit/km2 while maximum density of them is reach to 46 depression/km2. Circularity index and long/short axis ratios of dolines show that depressions don’t have an important elliptical shape and they protect their circularity characteristics. Also nearest neighbour index and value of nearest distance indicate that distribution of the forms is random. This situation arises from absence of a tectonic factor affecting doline distribution on plateau surface. But rose diagrams show that long axis of the dolines extend along NE-SW direction in parallel with the general direction of extension of mountains. Also it indicates that there is a significant relationship between long axis of the uvalas and lineaments obtained from satellite images and paleovalley axis. These relationships display that karstic dissolution start with the gaps between the inclined layer surfaces and continue following paleovalley axis.

Scattering Centers Detection and Tracking in Refocused Spaceborne SAR Images for Infrastructure Monitoring

Infrastructure monitoring applications can require the tracking of slowly moving points of a certain structure. Given a certain point from a structure to be monitored, in the context of available spaceborne synthetic aperture radar (SAR) products, where the image is already focused in a slant range—azimuth grid, it is not obvious if this point is the scattering center, if it is in layover or if it is visible from the respective orbit. This paper proposes a scattering centers detection and tracking procedure based on refocusing a set of SAR images on a provided high-resolution grid of the structure. The refocusing procedure is designed for high-resolution spotlight and sliding spotlight SAR images and consists of an azimuth defocusing followed by a modified back-projection algorithm on the given set of points. The scattering centers of the refocused image are detected in the 4-D tomography framework by testing if the main response is at zero elevation in the local elevation–velocity spectral distribution obtained using the Capon estimator. The mean displacement velocity is estimated from the peak response on the zero elevation axis, whereas the displacements time series for detected single scatterers is obtained as phase difference of complex amplitudes. The algorithm is tested by simulations with an emphasis on its behavior for a low number of satellite passes and applied on real data acquired with the TerraSAR-X satellite over the Puylaurent dam. The relative displacements between scattering regions show very good agreement with in situ measurements.