Ionospheric Alfvén Resonances (IAR) have been observed in Eskdalemuir induction coil magnetometer data. In order to investigate the harmonic frequency separation, we have modelled the IAR using magnetic field strength and plasma mass density. We have used three models of electron density; the IRI, E-CHAIM and an adjusted IRI model using ionosonde data. We find that the IRI and E-CHAIM models perform best.
The Greenland Telescope (GLT) has been operating in Greenland. It regularly participated in (sub-)mm Very Long Baseline Interferometry (VLBI) observations of the supermassive black hole. This paper summarizes the status and accomplishments of the telescope and its plan for the coming decades.
This paper presents the preliminary results of synthetic aperture radar (SAR) imaging of the Earth’s surface obtained using both passive and active radar sensors at the same time. The measurement was carried out during a dedicated measurement campaign held in Poland. As part of the exercise, selected region(s) of the Earth’s surface were imaged using the C-band frequency modulation continuous wave (FMCW) active radar, and the DVB-T-based passive radar at the same time. Both radars were mounted on the light manned aircraft. The main goal of this measurement was to test a fusion possibility of the data acquired from both the active and passive SAR imaging taken in different frequency bands. Thanks to various properties of these radar systems such as foliage penetration capabilities of the passive radar operating at the low UHF frequency and/or high resolution of the C-band active radar, and based on different scattering phenomena (forward/backward) - the fusion of both technologies might provide new yet unexplored possibilities for target recognition and classification. What is more, thanks to the different reflection properties of the targets at different frequencies, different waveforms and different geometries used (a monostatic one in the case of active radars, and a bistatic-in the case of passive radars), such a combined configuration may open new opportunities for measuring other target features than in the case of the individual systems operated separately.
In this paper, we describe the design and development status of a room-temperature C-band Phased Array Feed (PAF) demonstrator, based on Radio Frequency System-on-Chip (RFSoC) for radio astronomy application, to be installed on the Sardinia Radio Telescope. The instrument is optimized to work across the 4.75-6.00 GHz radio frequency (RF) band. The project of the front-end includes a compact RF module based on an 8×8 array of linear dual-polarization antenna elements integrated with Monolithic Microwave Integrated Circuit (MMIC) Low Noise Amplifiers (LNAs). In the preliminary version of the front-end project, which considers only one linear polarization, a subset of 32 elements are connected to the LNAs, while the rest of them are terminated to 50 Ohm matched loads. A dedicated signal acquisition chain of microwave components, based on two stages of filtering and signal conditioning, permits the injection of the 32 RF signals to the two commercial back-ends based on RFSoC digital boards. Each board is equipped with 16 inputs, with 1.25 GHz instantaneous bandwidth, and performs the frequency channelization, the partial and final beamforming of at least four independent beams (the number of beams may vary depending on the observation requirements). A general description of the front-end design, the back-end hardware, firmware and software development and an optimizer for the whole system performances evaluation, is presented.
In this work, we explore the design and applications of spatially-dispersive beam-steering metasurfaces. Such innovative devices consist of cascaded Huygens meta-atoms optimized to exhibit an engineered profile of their transmission phase vs. the incidence angle of the impinging wave. Differently from conventional beam-steering metasurfaces, the proposed devices exhibit a refraction effect that is strongly angle-dependent and may find application in several scenarios of future wireless systems.
In order to calculate photonic devices with slowly varying structural variation along propagation direction, we develop finite element beam propagation method (FE-BPM) with coordinate transformation. In this approach, converting a longitudinally varying waveguide into equivalent straight waveguide, cumbersome processes in FE-BPM, such as mesh updating process, is avoided. We employ this simulation technique in shape optimization of photonic devices and show a design example of mode converter.
We deduce the cold electron plasma density from NASA Van Allen Probes measurements throughout 2012-2019. We then extract two of the plasmasphere boundaries. We first use the gradient method for locating the plasmapause at Lpp and, then, the $100\mathrm{~cm}^{-3}$ density threshold for the plasmasphere outer edge located at L100. The sharp gradient of the plasmapause is only defined in 53% of cases, while L100 is defined for $\sim 85\%$ of cases. Differences and similarities between Lpp and L100 are discussed. L100 is demonstrated to bound the plasmasphere at large L-shell in the dusk where Lpp gradients often lack. We generate new empirical density models of the plasmasphere boundaries binned by L-shell, magnetic local time (MLT), and the maximum of the Kp index over 24 hours (Kp*).
Equatorial plasma bubbles (EPB) refer to the area of low electron density in the Earth’s ionosphere near the equator during post sunset and post-midnight. They influence the radio communications and GPS signals. In this work, we study the EPB occurrences and characteristics using the VHF radar images observed at the Chumphon station, Thailand, near the magnetic equator.. We develop an EPB image detection system using a hybrid learning technique with convolutional neural network (CNN) and support vector machine (SVM) and evaluate the accuracy of the proposed CNN-SVM model using two kernels: polynomial kernel and radial basis function (RBF) kernel.
GNSS-LEO radio links from Precise Orbital Determination (POD) and Radio Occultation (RO) antennas have been used increasingly in studying and monitoring the global ionospheric electron density $(N_{e})$. In this study we developed an optimal estimation (OE) method to retrieve Ne profiles from the slant total electron content $(hTEC)$ measurements acquired by the GNSS-POD links at negative elevation angles. The hmF2 and NmF2 from the OE retrieval are validated against ground-based ionosondes and radar observations, showing generally good agreements in NmF2 from all sites. Nighttime hmF2 measurements tend to agree better than the daytime when the ionosonde heights tend to be slightly lower. The OE algorithm has been applied to all GNSS-POD data acquired from the COSMIC-1 (2006-2019), COSMIC-2 (2019-present), and Spire (2019-present) constellations, showing a consistent ionospheric $N_{e}$ morphology. A detailed analysis of the frequency-wavenumber spectra is made for the $N_{e}$ variability at different heights. In the lower ionosphere (~150 km) we found significant spectral power in DE1, DW6, DW4, SW5, and SE4 wave components, in addition to well-known DW1, SW2 and DE3 waves. In the upper ionosphere (~450 km), additional wave components are still present, including DE4, DW4, DW6, SE4 and SW4. The co-exist of eastward and westward propagating WN4 components implies the presence of a stationary planetary wave4 (sPW4), as suggested by other earlier studies.
Methods of measuring the array antenna position of the Meridian II Project at Mingantu Observing Station are discussed.
Polarimetric synthetic aperture radar (PolSAR) has the advantage of all-day and all-weather work, which can obtain high-resolution radar images and polarimetric scattering matrix of the target. The dual polarimetric SAR can obtain a wider observation swath with lower energy budget than quad-pol SAR. In this paper, the pseudo quad-pol SAR data is reconstructed from dual polarization SAR data based on the proposed deep convolutional neural network. The urban damage level mapping index is established based on the co-polarization coherence pattern and the reconstructed quad-pol SAR data. The experiments have been conducted on the multi-temporal ALOS/PALSAR data from the March 11 Eastern Japan earthquake. Compared with the existing quad-pol SAR data reconstructed method, the proposed method has superior reconstruction performance. The quantitative experiment results indicate the proposed method can effectively achieve urban damage level mapping based on the dual polarization SAR data.
We show the basic characteristics of a phased array of dielectric tapered antenna operating at 300-GHz band based on a simulation. We examined antenna gain, radiation pattern, and beam steering characteristics. In the 4-element linear array configuration, we achieved the maximum antenna gain of 17.4 dBi and the beam steering range of ± 31 °.
This paper shows successful demonstration of underwater optical communication underwater optical wireless communication experiments at the transmission bitrate of 1 Gbps x transmission length of 100 m in the sea depth of 900 m off the coast of Sagami Bay using our developed equipment. We also evaluate optical transmission limits in underwater based on experimental results and theoretical optical attenuation in underwater.
We present the first experimental demonstration of a photonic-enabled wireless link using Continuous Phase Modulation in the sub-terahertz (sub-THz) frequency range. A carrier of 90 GHz is photonically generated and modulated by a 2.5Gbit/s signal with spectral efficiency of 1 (bit/s)/Hz. The receiver is placed at a distance up to 1.80 m and relies on an electronic approach.
The Lunar Surface Electromagnetics Explorer, LuSEE-Night, is a low frequency radio astronomy experiment which detects the cosmic Dark Ages signal on the radio-quiet farside of the Moon. The LuSEE-Night carries a radio frequency spectrometer consisting of a set of antennas, analog and digital processing electronics and will be launched in 2025 by the NASA Commercial Lunar Payload Services (CLPS). The initial stage of testing for the engineering model (EM) was performed for the analog amplification and filtering chain of the radio spectrometer. We confirmed that the EM of the preamplifier satisfies all the requirements for LuSEE-Night. The digital data acquisition, digital processing, command/control and telemetry are currently being developed with flight model hardware scheduled to be shipped to the integration site in early 2024.
In recent years, the research and development of high-speed and long-distance underwater optical wireless communication technology using visible light have been encouraged for undersea resource development and shallow-water leisure applications. This paper introduces the fundamentals of underwater optical wireless communication technology, technical issues, recent R&D trends, and the authors’ recent research outcomes.
In the article the method of user terminal position estimation using the broadcast signals transmitted in the downlink of the NB-IoT interface was presented, including the analysis of the radio channel influence on precision of position estimation as well as the eNodeB (Evolved Node B) synchronization. The practical ability to estimate the position in the test area has been verified in the laboratory conditions, using the reference signals with a variable signal-to-noise ratio and different radio channel profiles. Additionally, the method that allows increasing the precision of the terminal position estimation without the need of increasing the sampling frequency of the radio signal is presented.
A holographic optical element (HOE) is proposed as a substitution for the fine pointing mechanism (FPM) in underwater wireless communication. The proposed HOE has a function to couple the receiving beam to the single-mode fiber and stabilize the coupling efficiency. As a result of the experiment simulating an underwater communication environment, the HOE shows the potential to stabilize the coupling efficiency without mechanical feedback systems such as the FPM.
