Large Radio Telescope Research Articles

Light-tracing based surface deformation measurement strategy for large radio telescopes

Light-tracing based surface deformation measurement strategy for large radio telescopes

Design of the tertiary optical system for the Large Latin American Millimeter Array radio telescope

Design of the tertiary optical system for the Large Latin American Millimeter Array radio telescope

Scientific preparation for JRT: Wind pressure prediction model for large radio telescope based on real data from multi-sensors

Jingdong 120-meter radio telescope (JRT) is poised to become the world's largest single-aperture fully steerable medium-low frequency radio telescope. However, like other large-aperture radio telescopes, the JRT is vulnerable to wind loads, which can cause structural deformation and pointing errors. Addressing this challenge requires the ability to predict dynamic winds in real-time. This study developed a wind pressure preprocessing and prediction model using sensor data collected from the Kunming 40-meter radio telescope (KRT), enabling real-time prediction of wind pressure on the telescope. The model employs adaptive noise and Variational Mode Decomposition (VMD) techniques to eliminate random noise from the original wind pressure data. Subsequently, wind pressure predictions are made using a Bidirectional Long Short-term Memory (BiLSTM) model. By conducting predictions under various stabilization conditions and conducting a thorough analysis of measurement data from five sensors, the study has achieved impressive results in predicting wind pressure on the KRT reflector surface. The proposed model demonstrates the lowest MAE, RMSE, and MAPE, while achieving the highest R2 across various data sets. Where the average R2 of the proposed model is 0.9392 at 45° pitch angle attitude and the RMSE, MAE and MAPE values are 1.4923, 1.2377 and 1.82% respectively. This model helps wind load monitoring of real-time wind pressure monitoring of the telescope surface, to study the effects of wind load on pointing accuracy. By adjusting the control parameters to reduce wind load interference, to ensure the high-precision work of a large radio telescope, such as JRT.

Adjustment Method of Main Reflector for a Large Radio Telescope

The performance of the antennas, which plays an important role in millimeter-wave astronomy and space communication, is often limited by their reflector surface accuracy. Microwave holography is a fast and effective technique for measuring the surface profile of reflector antenna. In this paper, the antenna aperture phase profile is obtained by microwave holography to estimate the deviation between the reflector of the Tianma 65 m radio telescope and the ideal paraboloid. The panels of the Tianma 65 m radio telescope is in radial pattern with 14 rings. Each corner of the panel is fixed on the screw of the actuator to move up and down, and the adjacent corners of the four panels share an actuator. We use the method of plane fitting to calculate the adjustment value of every panels corner. But one actuator, which simultaneously controls the common corner of the adjacent panels, will have different adjustment values according to the plane fitting equation based on adjacent panels. In this paper, an adjustment value at the corner of the adjacent panel is obtained by plane fitting and adjustment calculation method with the antenna illumination function as the weight, that is, the optimal adjustment value of 1104 actuators of the Tianma 65 m radio telescope. Through many adjustments and the application of new algorithms, the surface accuracy of the reflector of the Tianma 65 m radio telescope has gradually improved to the current 0.24 mm.

Estimation of Pointing Errors of Large Radio Telescopes under Solar Radiation Based on Digital Twin

The pointing accuracy of large radio telescopes is affected by antenna structure errors, installation errors, servo errors, gravity, and varying environmental factors. Although an on-line pointing model had been developed in the past for several large radio telescopes to correct these effects, it is also valuable to explore new ways to correct these effects. Therefore, in order to estimate the dynamic pointing error of large radio telescopes under solar radiation, a new way based on digital twin (DT) is used in this paper. Digital models of the Wuqing 70-m radio telescope (WRT70) are created based on the DT operational framework. Finally, the reliability of the WRT70’s DT system is verified, and the dynamic pointing error of WRT70 (staying at the position of the elevation angle of 90° and the azimuth angle of 180°) on two sunny days in different seasons is estimated by the created DT system. The research results show that the pointing error of large radio telescopes under solar radiation fluctuates greatly and the seasonal differences are very striking. The maximum elevation pointing error of WRT70 under solar radiation around the winter solstice is over 40 arcsec, which is equal to 4/11 of the beam width for WRT70 operating at 8 GHz. In this paper, it is feasible to estimate the time-varying pointing errors of large radio telescopes at rest under solar radiation by constructing a DT system, but it is not effective to estimate the dynamic pointing errors of large radio telescopes in operation. It is expected to establish a dynamic pointing error model and calibrate the dynamic pointing errors of large radio telescopes in operation by DT technology in the future.

Pulsar candidate identification using advanced transformer-based models

Rapid and accurate identification of pulsars is a significant topic for large radio telescope surveys. With the enhancement of astronomical instruments, modern radio telescopes are witnessing an exponential increase in pulsar candidate detections. The application of artificial intelligence for the identification of pulsar candidates is an automated and highly effective solution to tackle the challenge of processing and recognizing vast volumes of data. In this work, using the data released by two surveys, the Commensal Radio Astronomy FasT Survey (CRAFTS) and High-Time Resolution Universe (HTRU), we propose a new framework to identify pulsar candidates. Firstly, due to the small number of real pulsars, we compare the performance of different data augmentation methods and find that the pulsar samples generated by the Deep Convolutional Generative Adversarial Network (DCGAN) based on deep learning techniques are closer to real pulsars. Secondly, we use two transformer-based classification models, Vision Transformer (ViT) and Convolutional Vision Transformer (CvT), to classify pulsar candidates, and find that the evaluation indexes of pulsar candidate classification based on two transformers can reach 100%. Finally, we use the t-distributed Stochastic Neighbor Embedding (t-SNE) algorithm to visualize the results of our identification framework. The results showed that pulsar and non-pulsar samples are separated from each other in multidimensional space. Therefore, it is a new attempt to apply transformer technology to pulsar candidate classification, and it could be of great significance to subsequent theoretical research.

A Study on the Mechanical Characteristics and Wheel–Rail Contact Simulation of a Welded Joint for a Large Radio Telescope Azimuth Track

The azimuth track is an important component of the radio telescope wheel–rail system. During operation, the azimuth track is inevitably subject to phenomena such as track wear, track fatigue cracks, and impact damage to welded joints, which can affect observation accuracy. The 110 m QiTai radio telescope (QTT) studied in this paper is the world’s largest fully steerable radio telescope at present, and its track will bear the largest load ever. Since the welded joint of an azimuth track is the weakest part, an innovative welding method (multi-layer and multi-pass weld) is adopted for the thick welding section. Therefore, it is necessary to study the contact mechanical properties between the wheel and the azimuth track in this welded joint. In this study, tensile tests based on digital image correlation technology (DIC) and Vickers hardness tests are carried out in the metal zone (BM), heat-affected zone (HAZ), modified layer, and weld zone (WZ) of the welded joint, and the measured data are used to fit the elastic–plastic constitutive model for the different zones of the welded joint in the azimuth track. Based on the constitutive model established, a nonlinear finite element model is built and used to simulate the rolling mechanical performance between the wheel and azimuth track. Through the analysis of simulated data, we obtained the stress distribution of the track under different pre-designed loads and identified the locations most susceptible to damage during ordinary working conditions, braking conditions, and start-up conditions. The result can provide a significant theoretical basis for future research and for the monitoring of large track damage.

Low-frequency Radio Interferometric Array Imaging Pipeline Optimization Based on Distributed Execution Framework

The Square Kilometre Array (SKA) project is an international collaboration to build the world’s largest radio telescope, whose sensitivity and measurement speed will be an order of magnitude higher than those of all current radio telescopes. Radio continuum survey is one of the main observation mode of the SKA, and the establishment of a standard map of the survey area based on continuum imaging will provide an important foundation for subsequent astronomical science. The GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended (GLEAM-X) is a project of the SKA pilot telescope Murchison Widefield Array (MWA) in 2018—2020. GLEAM-X is a new radio continuum survey project to be carried out with the MWA Phase II expansion array in 2018—2020. The experience of optimizing the imaging pipeline based on the distributed execution framework will help to solve the problem of massive data processing. In this paper, we describe the process steps of GLEAM-X imaging pipeline, integrate and improve it, and realize parallel processing of multiple pipelines on the China SKA Regional Centre Prototype (CSRC-P), and verify the deployment and test the correctness of the imaging pipeline system using GLEAM-X observation data. The GLEAM-X observations were used to validate the deployment of the imaging pipeline system and test its correctness. Then, to optimize the pipelines and improve the processing efficiency, the Data Activated Liu Graph Engine (DALiuGE) was used to integrate the imaging pipelines into the DALiuGE execution framework to automate the distributed parallel processing of the pipelines. Performance tests and results’ analysis show that the optimized imaging pipeline based on the DALiuGE execution framework has better performance, more flexible adaptability, and scalability than the traditional parallel approach, and can support future large-scale continuum imaging experiments during the first phase of SKA commissioning.

Analysis of Temperature Field of Very Large Aperture Radio Telescope

With the increase of antenna aperture and frequency, the influence of solar heat on its performance becomes more and more serious. In this paper, the thermal model of the 110 m aperture radio telescope to be built in Xinjiang is established to study its temperature field characteristics on the summer solstice. The results are as follows: during the day, the highest temperature of the main reflector can reach 42.86∘C, which appears at 14 o’clock, and the temperature of the legs also reaches the peak of 41.74∘C at the same time. The horizontal temperature difference of the back frame will exceed 1∘C at 5, 18, and 19.5 o’clock, the antenna pointing performance will be greatly affected. The temperature field at night is also not uniform, and the temperature difference of the pitching structure is significantly higher than that of other components, with the maximum temperature difference of 6.42∘C. Through the method of numerical simulation and test, it is proved that the wall thickness difference of components is the main reason for the large temperature difference at night.

Modeling the effects of power efficient approximate multipliers in radio astronomy correlators

Large scale Radio Telescopes for Radio Astronomy highly depend on the availability of large (digital) processing capacities for imaging. Estimates concerning power efficiency for future Radio Telescopes lead to anticipated power consumption numbers beyond feasibility. To reduce the power budget, the use of approximate multipliers within the correlator is explored. A baseband equivalent executable model of a radio synthesis telescope is constructed to assess the effects of approximate multipliers. Besides ideal multipliers with floating point accuracy, the use of accurate 8-bit multipliers and 4 different types of approximate multipliers is explored. For each of these multipliers, the energy efficiency of an individual multiplier is known and used to determine the energy efficiency improvement of a correlator when using approximate multipliers. The effects of approximation are quantified by 3 metrics (Signal-to-Noise-Ratio (SNR), Spurious-Free-Dynamic-Range (SFDR) and Root-Mean-Square (RMS) level) derived from maps constructed by the executable model based on an empty sky with only a single point source. This is considered to be the worst case scenario. For illustration purposes, a more realistic input is processed by the model as well. The metrics have been determined based on different SNR levels at the input of each antenna element. For input SNR levels up to 10 dB, all types of approximate multipliers used in this paper can be exploited to improve energy efficiency of correlators, leading to a maximum energy reduction of 19 %. For input SNR values up to 30 dB an energy improvement up to 12 % can be achieved. These percentages are based on implementations in a 40nm low power IC technology at 1 GHz.

Learning-based surface deformation recovery for large radio telescope antennas

Abstract The surface deformation of the main reflector in a large radio telescope is closely related to its working efficiency, which is important for some astronomical science studies. Here, we present a deep learning-based surface deformation recovery framework using non-interferometric intensity measurements as input. The recurrent convolutional neural network (RCNN) is developed to establish the inverse mapping relationship between the surface deformation of the main reflector and the intensity images at the aperture plane and at a near-field plane. Meanwhile, a physical forward propagation model is adopted to generate a large amount of data for pre-training in a computationally efficient manner. Then, the inverse mapping relationship is adjusted and improved by transfer learning using experimental data, which achieves a 15-fold reduction in the number of training image sets required, which is helpful to facilitate the practical application of deep learning in this field. In addition, the RCNN model can be trained as a denoiser, and it is robust to the axial positioning error of the measuring points. It is also promising to extend this method to the study of adaptive optics.

Quantum radio astronomy: Quantum linear solvers for redundant baseline calibration

The computational requirements of future large scale radio telescopes are expected to scale well beyond the capabilities of conventional digital resources. Current and planned telescopes are generally limited in their scientific potential by their ability to efficiently process the vast volumes of generated data. To mitigate this problem, we investigate the viability of emerging quantum computers for radio astronomy applications. In this a paper we demonstrate the potential use of variational quantum linear solvers in Noisy Intermediate Scale Quantum (NISQ) computers and combinatorial solvers in quantum annealers for a radio astronomy calibration pipeline. While we demonstrate that these approaches can lead to satisfying results when integrated in calibration pipelines, we show that current restrictions of quantum hardware limit their applicability and performance.

Surface shape detection methods for large radio telescopes

Surface shape detection methods for large radio telescopes

The measurement and modeling of gravitational deformation for large radio telescope based on wavefront perturbation method

The measurement and modeling of gravitational deformation for large radio telescope based on wavefront perturbation method

Active Disturbance Rejection-based Double-loop Control Design for Large Antenna's Servo System

Radio astronomical observations put stringent requirements on the tracking and pointing accuracy of radio telescope antennas. High inertia, low stiffness, underdamped, and multi-resonant frequencies of a large aperture radio telescope’s antenna make the high-accuracy control difficult. It is not easy to satisfy control performance using only conventional PID controllers. A low-order Active Disturbance Rejection-based double-loop controller for large antenna is designed in this paper and tested on the Green Bank Telescope model. First, the first-order Linear Active Disturbance Rejecting Controller (LADRC) cascading a first-order low-pass filter and a notch filter is designed for the antenna’s velocity loop to achieve the dual-objective optimal velocity tracking. Second, the position loop controller is designed to realize the antenna’s position-tracking control by combining the PD controller and a low-pass filter. Further optimization of the position-loop controller helps improve the dynamic performance of the system. The simulation results indicate that the response curves of the proposed PD-LADRC control are smother than those of the Quantitative Feedback Theory (QFT) based controller; the settling time of the PD-LADRC system is 10.1 s and reduces by about 8.2 s than that of the QFT. While using a better position controller reduces settling time to 5 s. The PD-LADRC system also has better wind-disturbance rejection; the worst disturbance response reduces at the gearbox by 68.3% and 60% at the dish, and the recovery time reduces by more than 15 s than the QFT-based controller. In addition, besides easier parameter tuning, the proposed PD-LADRC has better robustness to systematic parameter perturbations and minor tracking error rms in position tracking.

Antenna Pattern Modeling Accuracy for a Very Large Aperture Array Radio Telescope With Strongly Coupled Elements

Modern radio telescopes strongly rely on accurate computational electromagnetic tools for “beam” models. Especially for densely-packed aperture array radio telescopes, the only feasible way to produce accurate models of the individual embedded element patterns is by using electromagnetic codes. In this paper, the accuracy of two models computed by different commercial codes is evaluated for one station of the SKA-Low radio telescope. Except for a couple of critical frequencies, the amplitude and phase errors are low enough to allow a beamformer efficiency higher than 99%.

Measurements and Evaluations of the Atmospheric Transparency at Short Millimeter Wavelengths at Candidate Sites for Millimeter- and Sub-Millimeter-Wave Telescopes

Radio astronomical observations at millimeter and submillimeter wavelengths are a very important tool for astrophysical research. However, there is a huge area in northeastern Eurasia, including the whole Russian territory, which lacks sufficiently large radio telescopes effectively operating at these wavelengths. In this review, we describe our long-term efforts to find suitable sites for such radio telescopes in this area, that is, sites with good atmospheric transparency at millimeter and submillimeter waves. We describe methods and instruments used for measurements and evaluations of the atmospheric opacity. They include special radiometric systems, which are used for estimations of the atmospheric opacity in the transparency windows from the sky brightness measurements. Evaluation of the precipitable water vapor from such measurements by the artificial neural network is discussed. Other approaches use water vapor radiometers, global atmospheric models and signals of the Global Navigation Satellite Systems. To date, long-term radiometric monitoring has been performed at several candidate sites, and atmospheric conditions for many sites have been evaluated using global atmospheric models. Several sites with the best atmospheric transparency at millimeter and submillimeter wavelengths have been selected. They can be effectively used for astronomical observations, at least in the major atmospheric transparency windows at 1.3 mm and 0.85 mm. In general, the results show that northeastern Eurasia is a promising area for submillimeter astronomy. These results can also be used for space communications and radar systems.

A High-Temperature Superconducting Wideband Bandpass Filter at the L Band for Radio Astronomy

In order to ensure the normal operation of radio astronomy observations, an extremely sensitive receiver system needs to be equipped in front of the large radio telescope. An 8-pole wideband high-temperature superconducting (HTS) filter using a Coplanar Spiral Resonator Structure with a passband of 1160∼1670 MHz is developed to suppress strong radio interference. The filter is fabricated on a 36 mm × 14 mm YBCO HTS film, which is deposited on a 0.5 mm thick MgO substrate. The minimum insertion loss measured in the liquid nitrogen temperature region is 0.03 dB, and the first parasitic passband appears at 2600 MHz. The measured results are in good agreement with the simulations. The filter can be used in radio telescope receivers for the observation of neutral hydrogen and pulsars, as well as in high-sensitivity satellite navigation instruments.

The second data release from the European Pulsar Timing Array

Pulsar timing arrays offer a probe of the low-frequency gravitational wave spectrum (1–100 nHz), which is intimately connected to a number of markers that can uniquely trace the formation and evolution of the Universe. We present the dataset and the results of the timing analysis from the second data release of the European Pulsar Timing Array (EPTA). The dataset contains high-precision pulsar timing data from 25 millisecond pulsars collected with the five largest radio telescopes in Europe, as well as the Large European Array for Pulsars. The dataset forms the foundation for the search for gravitational waves by the EPTA, presented in associated papers. We describe the dataset and present the results of the frequentist and Bayesian pulsar timing analysis for individual millisecond pulsars that have been observed over the last ~25 yr. We discuss the improvements to the individual pulsar parameter estimates, as well as new measurements of the physical properties of these pulsars and their companions. This data release extends the dataset from EPTA Data Release 1 up to the beginning of 2021, with individual pulsar datasets with timespans ranging from 14 to 25 yr. These lead to improved constraints on annual parallaxes, secular variation of the orbital period, and Shapiro delay for a number of sources. Based on these results, we derived astrophysical parameters that include distances, transverse velocities, binary pulsar masses, and annual orbital parallaxes.

Moon Imaging Performance of FAST Radio Telescope in Bistatic Configuration with Other Radars

Ground-based radar has been used for Moon imaging for more than 60 years. Five-hundred-meter Aperture Spherical radio Telescope (FAST), as the largest radio telescope on Earth, holds significant potential for celestial imaging missions with its exceptional sensitivity. A bistatic Synthetic Aperture Radar (SAR) Moon imaging model that incorporates FAST and other transmitting radars is presented. The objective of this paper is to design the imaging parameters of this bistatic configuration based on the required resolution, and to estimate the resolution performance based on a given bistatic system capability. Considering the ultra-far range and the ultra-long observation time between the radars and the Moon, the geometric relationship involved in this bistatic configuration is significantly distinct from the bistatic configuration of airborne and spaceborne radars. Therefore, this paper accurately derives the two-dimensional resolution on the Moon’s surface. First of all, the models of the Earth’s surface and the Moon’s surface, and the celestial motion of the Earth and Moon are established using WGS-84 and JPL-DE421, given by STK. Secondly, the bistatic range history within the observation time is calculated in terms of continuous celestial motion instead of the popular ‘stop-and-go’ assumption. Thirdly, no approximation is used in the resolution derivation process, and, in addition to the two-dimensional resolutions, the incident angle and the included angle are also given to describe the imaging performance. This method can also be extended to other bistatic-station and single-station celestial imaging, providing support for radar location and parameters design, for observation time span selection, for observation area selection, and for imaging performance estimation. The echo generation and imaging for point targets set on the Moon are shown. The simulation results prove the validity and accuracy of the proposed method in the paper.