The Ghana Radio Astronomy Observatory

TL;DR

The Ghana Radio Astronomy Observatory (GRAO) transforms a decommissioned 32 m communications dish into a VLBI-capable instrument with wide sky coverage ($-77^{\circ}$ to $+88^{\circ}$ declination) and C-band receivers, enabling time-domain studies, maser spectroscopy, pulsar timing, and intercontinental VLBI. The project integrates a beam-waveguide optical path, dual-polarization feeds, and modern backends (ROACH2/DBBC) with a hydrogen maser timing standard, achieving high aperture efficiency and robust phase stability suitable for standalone science and cross-facility VLBI. Early science demonstrates 6.7 GHz methanol maser spectroscopy, Vela pulsar timing, and successful VLBI fringes on EVN baselines, validating GRAO’s readiness for routine operations and AVN participation. Collectively, GRAO advances Africa’s role in global radio astronomy, supports regional capacity building, and lays groundwork for SKA-era collaboration across the continent and beyond.

Abstract

The Ghana Radio Astronomy Observatory (GRAO) marks a pivotal advance in African radio astronomy through the successful transformation of a decommissioned 32 m satellite communication antenna into a scientifically capable, VLBI-ready radio telescope. Strategically located near the equator at Kutunse, Ghana, the telescope offers nearly full-sky coverage (-77 degrees to +88 degrees declination), making it a valuable asset for time-domain astronomy, transient surveys, and global VLBI networks. This work documents the technical evolution of the facility, including beam-waveguide optics, dual-polarization C-band receivers (5 and 6.7 GHz), and recent backend upgrades culminating in the integration of a hydrogen maser, wideband ROACH2 system, and enhanced control and pointing infrastructure. We report early science results from high-resolution spectral-line observations of 6.7 GHz Class II methanol masers, pulse timing of PSR J0835-4510 (Vela), and successful VLBI fringe detections on intercontinental baselines. Simulations and commissioning tests confirm high aperture efficiency (>77%), low sidelobe levels, and robust time stability across the signal chain. These outcomes validate the GRAO's readiness for both standalone and networked operations. As the first operational node in West Africa contributing to the African VLBI Network, GRAO plays a critical role in advancing the continent's participation in global radio astronomy, capacity building, and the preparatory phase of the Square Kilometre Array.

Figures (5)

• Figure 1: The Ghana Radio Astronomy Observatory
• Figure 2: Antenna performance simulation for the GRAO. Left panel: Normalized beam gain patterns at $5.0$ GHz and $6.7$ GHz, including sidelobe specifications (dashed lines). The simulations assume ideal optical alignment and a surface RMS error of $1.88$ mm. Right panel: Aperture efficiency as a function of elevation angle, incorporating surface deformation, atmospheric opacity, and pointing losses. Dashed vertical lines denote typical operational elevations ($30^\circ$, $45^\circ$, and $70^\circ$). Peak efficiencies match design specifications at zenith, while degradation at low elevation reflects expected structural and atmospheric constraints.
• Figure 3: Methanol maser observation towards Cepheus A HW2 with the Kutunse radio telescope in Ghana on 04 March 2025. The axes are labeled for flux density (Jy) and Velocity of local standard of rest.
• Figure 4: A 61-minute pulse profile of PSR J0835-4510 Vela pulsar taken with the GRAO telescope in August 2018.
• Figure 5: VLBI fringe tests to the GRAO telescope (Kutunse) on baselines to the telescopes in Medicina, Yebes, Zelenchukskaya and HartebeesthoekGurvits2021.