Volume 57 (2020): Issue 1-2 (April 2020)

A project called AntArr as a new application of the DBBC3 (Digital Base Band Converter, 3rd generation) is under development. A group of antennas operating at low frequency, in the range from 10 MHz up to 1500 MHz, are phased up for VLBI, pulsar and more recently for FRB observations. Part of the scientific programme is also dedicated to SETI activities in piggy-back mode. Dedicated elements can even be added to reach still lower frequencies to observe the range down to kHz frequencies. The DBBC3 manages the array operations in a selected portion of the band and the main characteristic is to synthesize a beam with an innovative approach. The final product of the array is a single station standard VLBI data stream for correlation with other antennas, or a synthesized beam for single dish observations. A number of antennas and array prototypes are under test at a location on the Etna volcano slope, with the aim to form a complete radio telescope of up to 1024 elements in 2020 and beyond. This project completes the lower part of the frequency spectrum covered in VLBI by the BRAND EVN project. The project AntArr is hosted and financed by HAT-Lab Ltd., which is the manufacturer of the DBBC family backends.

A novel cluster of sensitive detectors based on silicon photomultipliers (SiPM) is being developed for the Cherenkov gamma-ray telescope TAIGA-IACT (Tunka valley, Republic of Buryatia, Russia). The cluster will be able to detect Cherenkov radiation from extensive air showers in two wide bands: 250–300 nm (UV) and 250–700 nm (visible and UV). Each pixel consists of a Winston cone, 4 SiPMs with the total sensitive area of 144 mm², and readout electronics based on fast analogue memory. During operation in the UV band, a UV-bandpass filter is used to suppress cluster sensitivity in the visible range. In order to evaluate the detection efficiency of the selected SiPMs, a specific software simulator of SiPM output signal has been developed. This simulator takes into account such inherent parameters of SiPMs as total number of microcells, their recharge time, the dark count rate, the effective detection area, the quantum efficiency, the crosstalk between microcells, as well as conditions of SiPM operation, namely, the background noise and the Ohmic load in the readout (front-end) electronics. With this simulator it is possible to determine the expected trigger threshold under given conditions and parameters of selected detectors. Based on preliminary simulations, OnSemi MicroFJ-60035 SiPM chips have been chosen for the novel cluster of TAIGA-IACT. These SiPMs have sensible efficiency in the ultraviolet range (5–20% in the 250–300 nm band) and are distinguished by the presence of a fast output, which allows one to capture a low amplitude signal above a relatively high background noise.

Since 2017, the Institute of Applied Astronomy of the Russian Academy of Sciences in cooperation with the National Astronomical Observatories of the Chinese Academy of Sciences has been conducting observations of the Chang’E-3 lander carrier wave signal. The paper presents the features of observation scheduling and results of data processing. High-precision phase radar measurements have been obtained with an instrumental error of 1–2 mm. The deviation of residuals in model calculations does not exceed ± 1 cm. The estimates of CE-3 lander position have been obtained with an accuracy of 0.5’’, 7.4 m and 3.2 m in celenocentric cylindrical longitude, Px and Py coordinates, respectively.

Various feasible solutions of Irbene RT-32 secondary focus feed antennas are designed and compared in the present study. The examined feed antennas include smooth wall and corrugated horns with linear and shaped profiles. Mode matching technique is employed for simulation of scattering parameters and radiation patterns. Genetic algorithm is used for optimisation of horn profile for the best cross-polarization, and aperture efficiency performance. Although the presented horns are valid for any frequency band, different solutions allow choosing the best combination of factors, such as electrical parameters, bandwidth, physical size and complexity of manufacturing.

Data manipulation of the LOFAR Long-Baseline Calibrator Survey (LBCS) and the Westerbork Northern Sky Survey (WENSS) catalogues are carried out in the present study. The aim of the study is to make calibrator classification statistics plots and estimations for further observations and upcoming stations. First, mean flux densities of LBCS calibrators against declination and observed station baseline length to the tied core station are plotted and the classified sources are marked. Second, we provide the designation – naming it the success rate – for the number of sources with the correlated signal against all the LBCS catalogue sources. Third, there is a trend in mean peak flux densities between stations – longer the baseline, higher mean peak flux density. Finally, estimations for upcoming and recent stations are made and some results are not encouraging.

The present paper describes reduction procedures and imaging of radio astronomical data from the gravitational lens system CLASS B0631+519 acquired by e-MERLIN interferometer. The source has been previously imaged with VLA, MERLIN and the VLBA interferometers. Data reduction and polarisation calibration procedures will provide data on Faraday effects such as Faraday rotation and depolarization between lensed images that in turn carry information on large and small-scale magnetic fields in the lensing galaxy.

Reduction of data and imaging of the radio astronomical source have been achieved using Astronomical Image Processing System (AIPS) in conjunction with automatic data reduction pipelines that performed specific data processing steps. As a result, the sky map for the gravitational lens system has been successfully acquired and accuracy comparing the generated map to sky maps of the source produced by different authors has been confirmed.

The article discusses the issue of training of telecommunications engineers. The architecture of telecommunications solutions is changing very quickly. Obviously, training programmes must also change. Cybersecurity issues are one of the main drivers of change in telecommunications solutions and, therefore, training programmes. They have become the main issues in all processes related to digital transformation. At the same time, it is clear that the development of education in telecommunications clearly lags behind modern requirements. Such issues come to the fore in relation to the development of digital economy programmes. Cyber security issues for military telecommunications solutions are discussed separately.

Joint VLBI and SLR satellite tracking is a novel tracking approach to explore potential applications and to work out common procedures to coordinate observations between astronomical observatories in Latvia. Global Navigation Satellite System (GNSS) satellites equipped with laser retroreflectors have been chosen as test targets because they are accessible by both measuring techniques – satellite laser ranging (SLR) and Very Long Base Interferometry (VLBI).

The first Joint SLR and VLBI observations of selected GNSS satellites using three of Latvian large-scale astronomical utilities – VIRAC radio telescopes RT32 and RT16 (Ventspils International Radio Astronomy Centre of Ventspils University of Applied Sciences) with L band receivers and SLR station Riga (Institute of Astronomy of University of Latvia) were obtained in 2016 (NKA16) and 2017 (NKA41 and NKA42).

The paper describes the process of training a convolutional neural network to segment land into its labelled land cover types such as grass, water, forest and buildings. This segmentation can promote automated updating of topographical maps since doing this manually is a time-consuming process, which is prone to human error. The aim of the study is to evaluate the application of U-net convolutional neural network for land cover classification using countrywide aerial data. U-net neural network architecture has initially been developed for use in biomedical image segmentation and it is one of the most widely used CNN architectures for image segmentation. Training data have been prepared using colour infrared images of Ventspils town and its digital surface model (DSM). Forest, buildings, water, roads and other land plots have been selected as classes, into which the image has been segmented. As a result, images have been segmented with an overall accuracy of 82.9 % with especially high average accuracy for the forest and water classes.

Two factors of the existing GNSS Real-Time Kinematic (RTK) positioning are as follows: distance-dependence and unreliable ambiguity resolution under bad observation conditions in cities or forests. Use of multi-frequency GNSS signals and systems could possibly redefine RTK services in LatPos, regionally and globally, and more redundant measurements from multiple satellite systems, such as NAVSTAR, Galileo, Glonass and BeiDou, can improve the performance of RTK measurement results in terms of accuracy, availability, reliability and time to fix. The benefits of multiple systems of GNSS services are as follows: 1) savings in the reference station infrastructure costs, and 2) improvement on RTK preciseness and reliability for the professional users. The paper aims at studying how the RTK system, using multiple satellite constellations, performs, adding Galileo signal measurements. Galileo measurements are observed using a field receiver and corrections received from LatPos base station network. Numerical analysis is performed using real-time corrections in field receivers, and results from collected RINEX data are compared by various computing schemes, such as L1/L2 and wide lane signals, NAVSTAR and NAVSTAR with Galileo measurements. The results have preliminary demonstrated the significant improvement using both GNSS satellite signals. Further improvements on the LatPos system have been introduced and the planned improvements shown.