SA031-0013
Scintillometry Meets Interferometry: The Deployable Low-band Ionosphere and Transient Experiment (DLITE)

Tuesday, 15 December 2020
Poster
Joseph Helmboldt1, Blerta Bajramaj Markowski1, David Bonanno2, Tracy Clarke3, Jayce Dowell4, Brian C Hicks5, Namir E Kassim6 and Greg B Taylor4, (1)US Naval Research Laboratory, Washington, DC, United States, (2)US Naval Research Laboratory, Information Technology Division, Washington, DC, United States, (3)Naval Research Lab DC, 7200, Washington, DC, United States, (4)University of New Mexico Main Campus, Physics and Astronomy, Albuquerque, NM, United States, (5)Naval Research Lab DC, Washington, DC, United States, (6)Naval Research Laboratory, Washington, DC, United States
Abstract:
Density fluctuations within Earth’s ionosphere complicate radio-frequency astronomical observations, especially in the VHF regime (30—300 MHz). In particular, synthesis-imaging interferometers with baselines longer than a few km can lose coherence and be unable to image sources within this frequency regime. Conversely, these corrupted observations can serve as extremely precise probes of km-scale ionospheric structure on relatively short time scales (~seconds to minutes). It is not surprising then that in the past few decades, several unique investigations of ionospheric disturbances have been undertaken using telescopes such as the Very Large Array (VLA), the Long Wavelength Array (LWA), the Low Frequency Array (LOFAR), and the Murchison Widefield Array (MWA).

While these pioneering efforts have quite successfully elucidated several unique aspects of ionospheric structure, they suffer from a common shortcoming: portability. Establishing similar telescopes within other areas of interest is not economically feasible. Here, we describe efforts to develop a Deployable Low-band Ionosphere and Transient Experiment (DLITE) to address this. The DLITE system is an interferometer consisting of four LWA bent dipole antennas spread out over baselines of 200—400 m. The backend uses commercial off-the-shelf parts, including software-defined radios with the real-time “correlator” at its heart written in GNURadio. DLITE operates in the nominal band of 30—40 MHz, using time difference of arrival (TDOA) and frequency difference of arrival (FDOA) methods and nonlinear fitting techniques to isolate bright cosmic sources on the sky. By monitoring “A-Team” sources (Cygnus A, Cassiopeia A, Virgo A, Taurus A, Hercules A, and Hydra A) with a relatively wide bandwidth, the array can detect intensity and phase fluctuations from irregularities with strength parameters as small as CKL≈1027. We will discuss results from two DLITE systems currently operating in New Mexico and southern Maryland and plans for future deployments.

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