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LWA1 is a new radio telescope operating in the frequency range 10–88 MHz, located in central New Mexico. The telescope consists of 258 pairs of dipole-type antennas whose outputs are individually digitized and formed into beams. Simultaneously, signals from all dipoles can be recorded using one of the instrument's “all dipoles” modes, facilitating all-sky imaging. Notable features of the instrument include high intrinsic sensitivity (\approx\6 kJy zenith system equivalent flux density), large instantaneous bandwidth (up to 78 MHz), and four independently steerable beams utilizing digital “true time delay” beamforming. This paper summarizes the design of LWA1 and its performance as determined in commissioning experiments. We describe the method currently in use for array calibration, and report on measurements of sensitivity and beamwidth. [ABSTRACT FROM PUBLISHER]

Very-low-frequency (VLF) electromagnetic wave propagation is modeled for the first time over 1000 km scale distances using a 3-D finite-difference time-domain (FDTD) model of the Earth-ionosphere waveguide. Specifically, propagation paths of 2000 km in length are studied, with each simulation requiring 28k processing cores and over 45 h of real time and using ~3.9 TB. A variety of propagation scenarios are tested, including daytime and nighttime propagation paths, a realistic ground propagation path extending from the NAA VLF transmitter in Cutler, ME, USA, toward New Mexico, and day-to-night ionospheric transitions. The 3-D FDTD model results are compared with 2-D azimuthally symmetric FDTD and the long-wave propagation capability (LWPC) results to both validate the 3-D model and understand the impact a fully 3-D model can have on the propagation predictions. The results in this article identify under what conditions and also at what propagation distances, a fully 3-D model is most beneficial. [ABSTRACT FROM AUTHOR]