This article presents the design of the Radio Neutrino Observatory Greenland (RNO-G) and discusses its scientific prospects. Using an array of radio sensors, RNO-G seeks to measure neutrinos above 10 PeV by exploiting the Askaryan effect in neutrino-induced cascades in ice. We discuss the experimental considerations that drive the design of RNO-G, present first measurements of the hardware that is to be deployed and discuss the projected sensitivity of the instrument. RNO-G will be the first production-scale radio detector for in-ice neutrino signals.

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The balloon-borne HiCal radio-frequency (RF) transmitter, in concert with the ANITA radio-frequency receiver array, is designed to measure the Antarctic surface reflectivity in the RF wavelength regime. The amplitude of surface-reflected transmissions from HiCal, registered as triggered events by ANITA, can be compared with the direct transmissions preceding them by Oð10Þ microseconds, to infer the surface power reflection coefficient R. The first HiCal mission (HiCal-1, Jan. 2015) yielded a sample of 100 such pairs, resulting in estimates of R at highly glancing angles (i.e., zenith angles approaching 90°), with measured reflectivity for those events which exceeded extant calculations [P. W. Gorham et al., Journal of Astronomical Instrumentation, 1740002 (2017)]. The HiCal-2 experiment, flying from December 2016-January 2017, provided an improvement by nearly 2 orders of magnitude in our event statistics, allowing a considerably more precise mapping of the reflectivity over a wider range of incidence angles. We find general agreement between the HiCal-2 reflectivity results and those obtained with the earlier HiCal-1 mission, as well as estimates from Solar reflections in the radio-frequency regime [D. Z. Besson et al., Radio Sci. 50, 1 (2015)]. In parallel, our calculations of expected reflectivity have matured; herein, we use a plane-wave expansion to estimate the reflectivity R from both a flat, smooth surface (and, in so doing, recover the Fresnel reflectivity equations) and also a curved surface. Multiplying our flat-smooth reflectivity by improved Earth curvature and surface roughness corrections now provides significantly better agreement between theory and the HiCal-2 measurements. DOI: 10.1103/PhysRevD.98.042004 PHYSICAL REVIEW D 98, 042004 (2018) 2470-0010=2018=98(4)=042004 (19) 042004-1 © 2018 American Physical Society I. OVERVIEWThe NASA-sponsored ANITA project [1][2][3][4] has the goal of detecting the highest-energy particles incident on the Earth. Although designed for measurement of ultra-highenergy neutrinos interacting in-ice, the first ANITA flight also demonstrated (unexpectedly) excellent sensitivity to primary ultra-high-energy cosmic rays (UHECR) with energies exceeding 1 EeV (10 18 eV) [5] interacting in the Earth's atmosphere. These are assumed to be charged nuclei (likely protons), given the lack of efficient acceleration mechanisms for electrically uncharged particles, and the long lifetimes required to traverse megaparsec-scale distances. Through interactions with terrestrial matter, both neutrinos and charged cosmic-rays produce observable radio-frequency (RF) emissions via the Askaryan effect [6][7][8], with three important distinctions between the two experimental signatures:(1) as viewed from the airborne ANITA gondola, charged primary cosmic ray interactions in the atmosphere generally produce down-coming signals, which subsequently reflect off the surface and up to the gondola, whereas neutrinos interacting in-ice produce up-coming signals which refract through the surf...

The primary science goal of the NASA-sponsored ANITA project is measurement of ultra-high energy neutrinos and cosmic rays, observed via radio-frequency signals resulting from a neutrinoor cosmic ray-interaction with terrestrial matter (atmospheric or ice molecules, e.g.). Accurate inference of the energies of these cosmic rays requires understanding the transmission/reflection of radio wave signals across the ice-air boundary. Satellite-based measurements of Antarctic surface reflectivity, using a co-located transmitter and receiver, have been performed more-or-less continuously for the last few decades. Our comparison of four different reflectivity surveys, at frequencies ranging from 2-45 GHz and at near-normal incidence, yield generally consistent maps of high vs. low reflectivity, as a function of location, across Antarctica. Using the Sun as an RF source, and the ANITA-3 balloon borne radio-frequency antenna array as the RF receiver, we have also measured the surface reflectivity over the interval 200-1000 MHz, at elevation angles of 12-30 degrees. Consistent with our previous measurement using ANITA-2, we find good agreement, within systematic errors (dominated by antenna beam width uncertainties) and across Antarctica, with the expected reflectivity as prescribed by the Fresnel equations. To probe low incidence angles, inaccessible to the Antarctic Solar technique and not probed by previous satellite surveys, a novel experimental approach ("HiCal-1") was devised. Unlike previous measurements, HiCal-ANITA constitute a bi-static transmitter-receiver pair separated by hundreds of kilometers. Data taken with HiCal, between 200-600 MHz shows a significant departure from the Fresnel equations, constant with frequency over that band, with the deficit increasing with obliquity of incidence, which we attribute to the combined effects of possible surface roughness, surface grain effects, radar clutter and/or shadowing of the reflection zone due to Earth curvature effects. We discuss the science implications of the HiCal results, as well as improvements implemented for HiCal-2, launched in December, 2016.

The Radio Neutrino Observatory Greenland (RNO-G) is planned to be the first large-scale implementation of the in-ice radio detection technique. It targets astrophysical as well as cosmogenic neutrinos with energies above 10 PeV. The deep component of a single RNO-G station consists of three strings with antennas to capture horizontal as well as vertical polarization. This contribution shows a model-based approach to reconstruct the arrival direction of the neutrinos with an RNO-G station. The timing of the waveforms is used to reconstruct the vertex position. The shape and amplitude of the waveform are used to reconstruct the viewing angle. Together with the signal polarization it will add up to the neutrino arrival direction. We present the method used and the achieved angular resolution using the deep component of an RNO-G station.