An imaging algorithm for a lunar orbit interferometer array

Abstract

Radio astronomical observation below 30 MHz is hampered by the refraction and absorption of the ionosphere, and the radio frequency interference (RFI), so far high angular resolution sky intensity map is not available. An interferometer array on lunar orbit provides a perfect observatory in this frequency band: it is out of the ionosphere and the Moon helps to block the RFIs from the Earth. The satellites can make observations on the far side of the Moon and then send back the data on the near side part of the orbit. However, for such array the traditional imaging algorithm is not applicable: the field of view is very wide (almost whole sky), and for baselines distributed on a plane, there is a mirror symmetry between the two sides of the plane. A further complication is that for each baseline, the Moon blocks part of the sky, but as the satellites orbit the Moon, both the direction of the baseline and the blocked sky change, so even imaging algorithms which can deal with non-coplanar baseline may not work in this case. Here we present an imaging algorithm based on solving the linear mapping equations relating the sky intensity to the visibilities. We show that the mirror symmetry can be broken by the three dimensional baseline distribution generated naturally by the precession of the orbital plane of the satellites. The algorithm is applicable and good maps could be reconstructed, even though for each baseline the sky blocking by the Moon is different. We also investigate how the map-making is affected by inhomogeneous baseline distributions.

arXiv comment15 pages, 10 figures, AJ accepted

References in corpus (14)

• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• LOFAR: The LOw-Frequency ARray
• 21-cm cosmology
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
• The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm
• An Improved Model of Diffuse Galactic Radio Emission from 10 MHz to 5 THz
• Science with a lunar low-frequency array: from the dark ages of the Universe to nearby exoplanets
• Applying full polarization A-Projection to very wide field of view instruments: An imager for LOFAR
• Imprint of Intergalactic Shocks on the Radio Sky
• Software Holography: Interferometric Data Analysis for the Challenges of Next Generation Observatories
• Sky reconstruction from transit visibilities: PAON-4 and Tianlai Dish Array
• Brute-Force Mapmaking with Compact Interferometers: A MITEoR Northern Sky Map from 128 MHz to 175 MHz
• Sky reconstruction for the Tianlai cylinder array

Cited by in corpus (10)

• The Disk Substructures at High Angular Resolution Project (DSHARP): VII. The Planet-Disk Interactions Interpretation
• Discovering the Sky at the Longest wavelengths with a lunar orbit array
• Lunar Orbit Measurement of Cosmic Dawn 21 cm Global Spectrum
• Imaging sensitivity of a linear interferometer array on lunar orbit
• Large-scale Array for Radio Astronomy on the Farside
• On Measuring the 21 cm Global Spectrum of the Cosmic Dawn with an Interferometer Array
• The Electrical Design of a Membrane Antenna for Lunar-based Low-frequency Radio Telescope
• System equivalent flux density of Stokes I, Q, U, V of a polarimetric interferometer
• Synthesis imaging with a lunar orbit array: I. global sky map and its systematics
• System Equivalent Flux Density of a Polarimetric Tripole Radio Interferometer