Do Leonardo Da Vinci’s Drawings, Room Acoustics And Radio Astronomy Have Anything In Common?

After introducing Leonardo da Vinci’s (LdV) predecessors in the field of light propagation research, his drawings on the topic of focussing light through a spherical mirror are analysed. The discovery of LdV is presented, according to which, at an infinitely distant source of rays, a small fragment of the canopy is enough to generate a focus, while the rest of the mirror forms caustics for which LdV did not indicate an application. An analytical description of the energy concentration in the focus and on the caustics is given, together with its reference to the geometric representation of the acoustic field in rooms. Using symmetry in the description of energy relations in acoustics and electromagnetism, the interference that occurs on the caustics produced by the acoustic and electromagnetic wave is discussed. It is explained why in the sound field in existing halls, instead of a whole caustic only its cusp is observed, which is perceived as a point-like sound focus. The size of the mirror aperture, shown graphically by LdV, is determined. How the development of receiving techniques increased the mirror aperture compared to the LdV estimate is also shown. The implementation of these improvements is presented via the example of the Arecibo and FAST radio telescopes.

Monitoring the brightness temperature of the Moon throughout the lunar cycle from radio observations in the Ku band

Within the spectrum of radio waves, the Ku band (12 - 18 GHz ) stands out for the wide range of instruments available and for its relative ease of acquisition, given that satellite television operates in this band. This situation offers a great opportunity for the development of radio astronomy in countries with unfavorable climatic conditions for optical astronomy, since this band is only affected by dense masses of water vapor. In this article we present a methodology for the calibration of the receiver system of compact Ku-band radio telescopes, and its application in the determination of the brightness temperature of the Moon. Our methodology involves modeling the influence of the atmosphere of the Earth on the response of the radioreceptor, which minimizes the error in the calculation of the brightness temperature of the observed object. We applied the proposed methodology in the monitoring of the Lunar cycle using the Ku-band radio telescope of the Observatorio Astronomico of Universidad Tecnológica de Pereira, Colombia (OAUTP). After observing during May, June, and July of 2021, we obtained an average temperature of 213.15 K, with maximum and minimum values of 275.55 K and 150.75 K, respectively. In addition, we evidenced a delay of 5.75 days between the phase in which the maximum temperature is presented and the phase of the full Moon, which is consistent with the frequency of observation. The results show that our methodology is useful to optimize the calibration of compact Ku-band radio telescopes, and expand the potential of this type of instrument for the scientific study of radio sources other than the Sun, in this case the Moon.

New design of large fully-steerable radio telescope reflector based on homogenized mesh structure

The self-weight of a large fully-steerable radio telescope is one of the important factors affecting its performance. In the existing reflector system scheme, the problem of surface accuracy caused by its large and heavy structure has seriously restricted the application and implementation of large radio telescopes. Therefore, a new mesh structure scheme for a large fully-steerable radio telescope reflector is proposed in this paper. This scheme is based on a homogenized mesh back-up structure in the form of a quasi-geodesic grid and regular quasi-tri-prism or tetrahedron, which can significantly reduce the structural complexity and self-weight of the reflector under the condition that the reflector can meet the desired performance requirements. Finally, the feasibility and rationality of the scheme are evaluated by numerical simulation analysis, which has significant advantages and provides a new design for the reflector of a large fully-steerable radio telescope.

Constraining the axion–photon coupling using radio data of the Bullet cluster

Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near $$m_a \sim 20$$ m a ∼ 20 μeV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency $$\nu \sim 1{-}3$$ ν ∼ 1 - 3 GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion–photon coupling constant can be constrained to $$g_{a \gamma \gamma } \sim 10^{-12}{-}10^{-11}$$ g a γ γ ∼ 10 - 12 - 10 - 11 GeV$$^{-1}$$ - 1 for $$m_a \sim 20$$ m a ∼ 20 μeV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).

Short-baseline interferometry local-tie experiments at the Onsala Space Observatory

We present results from observation, correlation and analysis of interferometric measurements between the three geodetic very long baseline interferometry (VLBI) stations at the Onsala Space Observatory. In total, 25 sessions were observed in 2019 and 2020, most of them 24 h long, all using X band only. These involved the legacy VLBI station ONSALA60 and the Onsala twin telescopes, ONSA13NE and ONSA13SW, two broadband stations for the next-generation geodetic VLBI global observing system (VGOS). We used two analysis packages: $$\nu $$ ν Solve to pre-process the data and solve ambiguities, and ASCOT to solve for station positions, including modelling gravitational deformation of the radio telescopes and other significant effects. We obtained weighted root mean square post-fit residuals for each session on the order of 10–15 ps using group-delays and 2–5 ps using phase-delays. The best performance was achieved on the (rather short) baseline between the VGOS stations. As the main result of this work, we determined the coordinates of the Onsala twin telescopes in VTRF2020b with sub-millimetre precision. This new set of coordinates should be used from now on for scheduling, correlation, as a priori for data analyses, and for comparison with classical local-tie techniques. Finally, we find that positions estimated from phase-delays are offset $$\sim +3$$ ∼ + 3 mm in the up-component with respect to group-delays. Additional modelling of (elevation dependent) effects may contribute to the future understanding of this offset.

GNSS-based water vapor estimation and validation during the MOSAiC expedition

Within the transpolar drifting expedition MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate), GNSS was used among other techniques to monitor variations in atmospheric water vapor. Based on 15 months of continuously tracked GNSS data including GPS, GLONASS, and Galileo, epoch-wise coordinates and hourly zenith total delays (ZTD) were determined using a kinematic precise point positioning (PPP) approach. The derived ZTD values agree to 1.1 ± 0.2 mm (RMS of the differences 10.2 mm) with the numerical weather data of ECMWF’s latest reanalysis, ERA5, computed for the derived ship’s locations. This level of agreement is also confirmed by comparing the on-board estimates with ZTDs derived for terrestrial GNSS stations in Bremerhaven and Ny Ålesund and for the radio telescopes observing Very Long Baseline Interferometry in Ny Ålesund. Preliminary estimates of integrated water vapor derived from frequently launched radiosondes are used to assess the GNSS-derived integrated water vapor estimates. The overall difference of 0.08 ± 0.04 kg m−2 (RMS of the differences 1.47 kg m−2) demonstrates a good agreement between GNSS and radiosonde data. Finally, the water vapor variations associated with two warm air intrusion events in April 2020 are assessed.