Azimuth Axis Research Articles

A new calibration model for pointing a radio telescope that considers nonlinear errors in the azimuth axis

A new calibration model of a radio telescope that includes pointing error is presented, which considers nonlinear errors in the azimuth axis. For a large radio telescope, in particular for a telescope with a turntable, it is difficult to correct pointing errors using a traditional linear calibration model, because errors produced by the wheel-on-rail or center bearing structures are generally nonlinear. Fourier expansion is made for the oblique error and parameters describing the inclination direction along the azimuth axis based on the linear calibration model, and a new calibration model for pointing is derived. The new pointing model is applied to the 40m radio telescope administered by Yunnan Observatories, which is a telescope that uses a turntable. The results show that this model can significantly reduce the residual systematic errors due to nonlinearity in the azimuth axis compared with the linear model.

VLBI 전파망원경 기준 신호 전송시스템 안정화

A fiber-optic reference signal transmission system, which transmits the 1.4 GHz reference signal from H-maser to receiver cabin in radio telescopes, was adopted for compensating the phase changes due to temperature variation and antenna movement. At the first experiment, the remote signal's phase changed more than 15 degrees at 1.4 GHz. We found unstable components in sub-system experiments and replaced them. The main cause of unstable phase stability was the unaligned polarization axis between Laser Diode and Mach-Zehnder Modulator (MZM). The improved system stability showed <TEX>$1{\times}10^{-16}$</TEX> allan standard deviation at 1,000 sec integration time with the antenna fixed. When the antenna moves in the azimuth axis, the 1.4 GHz remote signal showed the phase change smaller than 0.2 degrees.

Ship Discrimination Using Polarimetric SAR Data and Coherent Time-Frequency Analysis

This paper presents a new approach for the discrimination of ship responses using polarimetric SAR (PolSAR) data. The PolSAR multidimensional information is analyzed using a linear Time-Frequency (TF) decomposition approach, which permits to describe the polarimetric behavior of a ship and its background area for different azimuthal angles of observation and frequencies of illumination. This paper proposes to discriminate ships from their background by using characteristics of their polarimetric TF responses, which may be associated with the intrinsic nature of the observed natural or artificial scattering structures. A statistical descriptor related to polarimetric coherence of the signal in the TF domain is proposed for detecting ships in different complex backgrounds, including SAR azimuth ambiguities, artifacts, and small natural islands, which may induce numerous false alarms. Choices of the TF analysis direction, i.e., along separate azimuth or range axis, or simultaneously in both directions, are investigated and evaluated. TF decomposition modes including range direction perform better in terms of discriminating ships from range focusing artifacts. In comparison with original full-resolution polarimetric indicators, the proposed TF polarimetric coherence descriptor is shown to qualitatively enhance the ship/background contrast and improve discrimination capabilities. Using polarimetric RADARSAT-2 data acquired over complex scenes, experimental results demonstrate the efficiency of this approach in terms of ship location retrieval and response characterization.

A sensitive method of determining optic axis azimuth based on laser feedback

A sensitive method to determine the optic axis azimuth of the birefringence element is presented, which is based on laser feedback. The phase difference between the two intensities in birefringence feedback changes with the angle between the optic axis of the birefringence element and laser original polarization. The phase difference is highly sensitive to the relative position of the optic axis and the laser original polarization. This method is used to highly precisely determine the optic axis azimuth, and is able to distinguish between the fast axis and the slow axis of the birefringence element. Theoretical analysis and experimental results are both demonstrated.

Design on Embedded Driving and Control System for Direct Current Servo Motor

Analyzed working principle of servo control system and applications of direct current (i.e. DC) servo motor in the two-dimensional (i.e. 2D) digital control system, used embedded PC104 processor as the central processing unit, selected DC servo motor whose model was J320LYX04C as azimuth axis motor, and DC servo motor whose model was J215LYX03E as pitch axis motor, constituted the executive body for servo system, and designed a driving and control system which can control the two-dimension turntable rotating precisely in space and lead CCD image sensor to catch and track target. Tests show that the system positioning accuracy meet the given requirements and the system with high reliability runs smoothly in the real application.

Two distinct shear wave splitting directions in the northwestern Deccan Volcanic Province

The northwestern Deccan Volcanic Province in India has witnessed several tectonic episodes resulting in the formation of rift zones, wide spread magmatism, and deep‐seated faults that are host to some deadly intraplate earthquakes. In this study, we attempt to decipher the mantle deformation beneath the region using the SKS splitting technique applied to high‐quality data from a regional network comprising 44 broadband seismic stations sited on diverse tectonic environments. The first measurements of 461 (312 SKS and 149 SKKS) splitting parameters from 117 earthquake sources reveal two major trends, one coinciding with the absolute plate motion (APM) of the Indian plate and the other roughly oriented in the E‐W direction. Forward modeling of the dependence of the splitting parameters on incoming polarization assuming horizontal axis of symmetry brings out two layers of anisotropy beneath the study region with the fast axis azimuths oriented N22°E in the bottom layer and N77°E in the top layer. While stronger anisotropy (δt∼1.2 s) in the bottom layer is related to asthenospheric flow, a weaker anisotropy (δt∼ 0.5 s) in the upper layer could represent anisotropy frozen in the lithosphere due to deformation related to widespread magmatism in this plume affected region.

Properties of a general azimuth–elevation tracking angle formula for a heliostat with a mirror-pivot offset and other angular errors

The solar field of a central receiver system (CRS) is an array of dual-axis tracking heliostats on the ground beside or around a central tower, with each heliostat tracking the sun to continuously reflect the solar beam onto the fixed tower-top receiver. Azimuth–elevation tracking (also called altitude–azimuth tracking) is the most common and popular tracking methods used for heliostats. A general azimuth–elevation tracking angle formula was developed previously for a heliostat with a mirror-pivot offset and other typical geometric errors. The angular error parameters in this tracking angle formula are the tilt angle, ψt, and the tilt azimuth angle, ψa, for the azimuth axis from the vertical direction, the dual-axis non-orthogonal angle, τ1 (bias angle of the elevation axis from the orthogonal to the azimuth axis), and the non-parallel degree, μ, between the mirror surface plane and the elevation axis (canting angle of the mirror surface plane relative to the elevation axis). This tracking angle formula is re-rewritten here as a series of easily solved expressions. A more numerically stable expression for the mirror-center normal is then presented that is more useful than the original mirror–normal expression in the tracking angle formula. This paper discusses some important angular parametric properties of this tracking angle formula. This paper also gives an approach to evaluate the tracking accuracy around each helistat rotational axis from experimental tracking data using this general tracking angle formula. This approach can also be used to determine the heliostat zero angle positioning errors of the two rotational axes. These supplementary notes make the general azimuth–elevation tracking angle formula more useful and effective in solar field tracking designs.

A correction method of encoder bias in satellite laser ranging system

In a satellite laser ranging telescope system, well-aligned encoders of the elevation and azimuth axes are essential for tracking objects. However, it is very difficult and time-consuming to correct the bias between the absolute-position indices of the encoders and the astronomical coordinates, especially in the absence of a finder scope for our system. To solve this problem, a method is presented based on the phenomenon that all stars move anti-clockwise around Polaris in the northern hemisphere. Tests of the proposed adjustment procedure in a satellite laser ranging (SLR) system demonstrated the effectiveness and the time saved by using the approach, which greatly facilitates the optimization of a tracking system.

Calculation and Simulation Azimuth Hydrostatic Thrust Bearing of a Large Alt-Azimuth Telescope

The use of hydrostatic bearing for support of telescope offers a number of potential performance advantages, but the structure parameter of bearing is the main factor which influence the bearing. The temperature rise of bearing is also important for the stiffnees of the telescope mount.In addition to the known benefit of mount stiffness and tracking accuracy from exceedingly low friction, the hydrostatic bearing provides a wide range of geometric possibilities for large telescopes [1].This paper analyzes various familiar hydrostatic bearing for the azimuth and elevation axes of telescope.Theoretical calculation and simulation show that the performance of bearing meets telescope’s design requirements.The principle and process of this work and Finite Element Analysis (FEA) are introduced in detail. According to the CFX result, the structure parameter and performance of bearing ,temperature field and pressure distribution have obtained.

Spatiotemporal contrast enhancement and feature extraction in the bat auditory midbrain and cortex

Navigating on the wing in complete darkness is a challenging task for echolocating bats. It requires the detailed analysis of spatial and temporal information gained through echolocation. Thus neural encoding of spatiotemporal echo information is a major function in the bat auditory system. In this study we presented echoes in virtual acoustic space and used a reverse-correlation technique to investigate the spatiotemporal response characteristics of units in the inferior colliculus (IC) and the auditory cortex (AC) of the bat Phyllostomus discolor. Spatiotemporal response maps (STRMs) of IC units revealed an organization of suppressive and excitatory regions that provided pronounced contrast enhancement along both the time and azimuth axes. Most IC units showed either spatially centralized short-latency excitation spatiotemporally imbedded in strong suppression, or the opposite, i.e., central short-latency suppression imbedded in excitation. This complementary arrangement of excitation and suppression was very rarely seen in AC units. In contrast, STRMs in the AC revealed much less suppression, sharper spatiotemporal tuning, and often a special spatiotemporal arrangement of two excitatory regions. Temporal separation of excitatory regions ranged up to 25 ms and was thus in the range of temporal delays occurring in target ranging in bats in a natural situation. Our data indicate that spatiotemporal processing of echo information in the bat auditory midbrain and cortex serves very different purposes: Whereas the spatiotemporal contrast enhancement provided by the IC contributes to echo-feature extraction, the AC reflects the result of this processing in terms of a high selectivity and task-oriented recombination of the extracted features.

Optic axis determination based on polarization flipping effect induced by optical feedback

For many materials, particularly biological tissues, optic axis orientation directly correlates with the materials performance, such as refractive index. In this Letter, a system measuring the optic axis azimuth was built using the laser feedback method that the polarization state of laser output is linearly polarized when optic axis azimuth is consistent with the initial direction of the laser polarization, otherwise elliptical polarization will be observed. The polarization state of the laser output is highly sensitive to the relative position of the optic axis and the initial direction of the laser polarization. This may be used to determine the optic axis azimuth of a material with a high precision.

Quantitative measurement of the distribution and alignment of collagen fibers in unfixed aortic tissues

Determination of the local amount and direction of collagen fibers during deformation is crucial for an understanding of the mechanical behavior of aortic tissues. Since most conventional methods cannot be used for this purpose, we propose a method to quantify the local amount and direction of fibers by simply measuring the optical properties of the specimen. After confirming the linear correlation between the retardance and thickness of sections of porcine thoracic aortas (PTAs) ranging from 15 to 300μm, we investigated the effects of their structural components, i.e., smooth muscle cells (SMCs), elastin and collagen, on the retardance of whole tissues. Decellularization of SMCs did not change the retardance of PTA sections significantly. Patterns in autofluorescent and immunofluorescent images of elastin purified from bovine nuchal ligaments did not match those in retardance images. Images of collagen in PTA sections stained with picrosirius red were similar to corresponding retardance images. The slow axis azimuth corresponded to the circumferential direction of the aorta. Results indicate that collagen in aortas can be quantified by measuring the retardance and slow axis azimuth of whole aortic tissues. Application of this technique to PTAs showed that retardance was higher in dorsal and distal regions than ventral and proximal regions, respectively, indicating that the aortas contain more collagen in distal and dorsal regions than proximal and ventral regions, respectively. Both results were in accordance with previous findings. Measurement of retardance is useful to quantify the amount of collagen in unfixed aortas.

Morphometric analysis of sinkholes in a karst coastal area of southern Apulia (Italy)

Salento, the southern portion of Apulia region (SE Italy), is a narrow and elongated peninsula in carbonate rocks, with prevailing low coastlines, locally interrupted by high rock cliffs. The long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes. As observed in many other karst coastal settings worldwide, development of sinkholes may be particularly severe along the coasts, where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes, even influencing the coastline evolution. Following a previous study, where the main features of sinkholes at Torre Castiglione (Taranto province) were investigated and described, and a preliminary susceptibility map produced, at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes. The main morphometric parameters generally used for sinkhole characterization have been considered in this study: shape of the sinkhole, azimuth and length of maximum and minimum axes, depth, elongation ratio, and distance from the shorelines. Each of them is described, both as individual parameter and in conjunction with the others, in the attempt to identify the main factors controlling development of sinkholes in the area, and their evolution as well. With regard to this latter aspect, beside simple morphometry of the sample of sinkholes at Torre Castiglione, we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities. To investigate the matter, a three-stage analysis has been carried out in this study by means of: field measurements of the fractures bounding the sinkholes, field measurement of the long axes azimuth of the elongated sinkholes, comparison of the previously described sets with the strikes of the main regional geological structures. The obtained results show, in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes, a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays. Eventually, the approach here presented may be applied in other karst coastal sinkhole-prone areas, to gain new knowledge on the genesis and evolution of coastal sinkholes, and to properly evaluate the hazard they pose to the anthropogenic environment.

1P161 方位と倒れの構造変化を1分子レベルで検出する偏光スイッチングを用いた新しいTIRFM(11.分子モーター,ポスター,日本生物物理学会年会第51回(2013年度))

1P161 方位と倒れの構造変化を1分子レベルで検出する偏光スイッチングを用いた新しいTIRFM(11.分子モーター,ポスター,日本生物物理学会年会第51回(2013年度))

A Fast and High-Accuracy Compass Alignment Method to SINS with Azimuth Axis Rotation

Azimuth axis rotating modulation was introduced to improve the alignment accuracy of strapdown inertial navigation system (SINS) through compass algorithm, in which the limit accuracy was determined by equivalent sensor errors in the eastern and northern direction. In this modulation, horizontal sensor errors were modulated into zero mean periodic variables. Furthermore, two methods were introduced to ensure alignment accuracy and speed: (1) shortened rotating cycle and redesigned compass parameters were selected to eliminate or ease the amplification to low-frequency senor error inputs in compass loop caused by rotation and (2) a data repeated calculation method was designed to shorten prolonged alignment time caused by the above redesigned parameters. Based on a certain SINS, turntable test proves that alignment accuracy and time were significantly improved and slightly shortened in comparison with the classical compass alignment.

Heterogeneity of deformation of aortic wall at the microscopic level: Contribution of heterogeneous distribution of collagen fibers in the wall

There is growing evidence of heterogeneous distribution of collagen fibers in the aortic wall. To investigate the effects of collagen microstructure on local aortic wall deformation, porcine thoracic aortas were sliced into 100 μm-thick sections perpendicular to their radial direction and stretched biaxially with a laboratory-made tensile tester under a microscope equipped with a birefringence imaging system. Strain tensor components were calculated from fluorescent images of the cell nuclei for each 50 × 50 μm² area. Retardance Ret and slow axis azimuth θ were measured as indices of collagen density and fiber direction, respectively. Aortic wall deformation was highly heterogeneous: standard deviations of strains were significantly larger, by 3-5 times, in aortic slices than in homogeneous silicone sheets. A significant negative correlation was found between maximum principal strain and Ret (R=-0.077), and a positive correlation between minimum principal strain direction and θ (R=0.345). These indicate that the aorta is less distensible in areas with higher collagen density and in the direction of collagen fiber alignment. Microscopic heterogeneity may induce heterogeneous responses of smooth muscle cells and have crucial effects on mechanical homeostasis in the aortic wall.

스텝핑 모터 특성에 따른 2축 짐발 안테나 시스템의 미소진동 측정 시험

A 2-axis gimbal system is one of main disturbance sources affecting image jitter response of a satellite. The gimbal system comprises azimuth stage and elevation stage, and these pointing mechanism can be rotated by stepping motors about its azimuth and elevation axes simultaneously. Because of the complex and coupled dynamic motion of the gimbal system, its moment of inertia and structural modes can be changed according to the system configuration, and thus the gimbal system generates complicated and non-linear disturbance characteristics. In order to improve the jitter response of a spacecraft, it is an indispensable process to reduce the micro-vibration disturbance level of the antenna system. In the present research, a 2-axis gimbal system was manufactured and then its micro-vibration test was performed in terms of two types of stepping motors(2-phase and 5-phase). The test results show that the disturbance level of the gimbal system can be reduced by replacing the 2-phase stepping motor with the 5-phase one, and the average disturbance attenuation ratio is 56 % in peak level and 48 % in standard deviation level. The experimental results confirm that it is an efficient jitter reduction method to adopt a high-phase stepping motor.

The boulder berm of Punta Saguerra (Taranto, Italy): a morphological imprint of the Rossano Calabro tsunami of April 24, 1836?

An extended berm of calcarenitic boulders is recognisable at Punta Saguerra, few kilometres south of Taranto (Apulia, Italy) while isolated boulders are sparse in other near localities. The berm is at 2–5 m above present sea level (a.p.s.l), on a rocky headland gently sloping toward the sea; it is separated from the coastline by a large terrace. A detailed study of its stratigraphy and its morphology has been performed in order to define its depositional mechanism; in particular, integrated DGPS and Laser Scanner surveys have provided precise details of each boulder: position, size and distance from the shoreline. The accumulation is constitute of boulders up to 30 tons, which locally are arranged in rows of embricated patterns. The surfaces of the biggest boulders are characterised by biogenic encrustations and by solution potholes that indicate their intertidal/adlittoral/spray zone provenience. Based on direct observations of each boulder (size, shape, weight and long axis azimuth), together with hydrodynamic equations it is possible to hypothesize the extreme event—geodynamic or meteorological— which was responsible for this singular accumulation. AMS age determinations on Vermetid sp. sampled on boulder surfaces and chronicle suggest that the accumulation may be attributed to the tsunami generated by the strong earthquake that occurred on April 24, 1836, the epicentre of which has been localised near Rossano Calabro, along the Ionian coast of northern Calabria.

Effect of plane-mirror installation errors on pointing errors in periscope-type satellite optical communication terminals

In a satellite optical communication system, the pointing error is an important factor that strongly influences the system performance. For periscope-type satellite optical communication terminals, installation errors of 45° plane mirrors in the coarse point apparatus (CPA) can lead to pointing errors. In this respect, we classify the installation errors of two 45° plane mirrors in the system and derive the corresponding “transfer” matrices to describe them. Furthermore, we establish mathematical models of the pointing error caused by installation errors of 45° plane mirrors. These models allow one to calculate and compensate the pointing errors in periscope-type satellite optical communication terminals. The results of our simulations show that the pointing errors vary with the elevation axis angle but do not depend on the azimuth axis angle. Compared to the side-angle error, the slope-angle error brings a larger pointing error. However, the mathematical model we developed allows one to compensate more than 99.9 % of the overall pointing error. The present work provides a theoretical basis for the design of periscope-type satellite optical communication terminals.

Determination of the angular parameters in the general altitude–azimuth tracking angle formulas for a heliostat with a mirror-pivot offset based on experimental tracking data

A set of general altitude–azimuth tracking angle formulas for a heliostat with a mirror-pivot offset and other geometrical errors were developed previously. The angular parameters with respect to the geometrical errors are the tilt angle, ψt, and the tilt azimuth angle, ψa, of the azimuth axis, the bias angle, τ1, of the altitude axis from the orthogonal to the azimuth axis, and the canting angle, μ, of the mirror surface plane relative to the altitude axis. In view of the importance the zero angle position errors of the two rotational axes (α0 is for the zero angle position error of the altitude axis and γ0 for the zero angle position error of the azimuth axis), the original general tracking angle formulae have been slightly modified by replacing the tracking angles in the original tracking formulas with the difference between the nominal tracking angles and the zero angle position errors. The six angular parameters (ψa, ψt, γ0, τ1, α0, μ) for a specific altitude–azimuth tracking heliostat could be determined from experimental tracking data using a least squares fit and the classical Hartley-Meyer solution algorithm. The least squares model is used on data for a specially designed heliostat model with two sets of laser beam tracking test data to show the effectiveness of the least squares model and the Hartley-Meyer algorithm.