3 years ago

Antarctic Surface Reflectivity Calculations and Measurements from the ANITA-4 and HiCal-2 Experiments.

D. Saltzberg, D. Z. Besson, E. Oberla, F. Wu, T. C. Liu, B. Hill, S. Stafford, W. R. Binns, P. W. Gorham, J. Lam, A. Novikov, H. Schoorlemmer, J. Nam, J. M. Clem, A. Ludwig, B. Strutt, K. Mulrey, M. Mottram, P. Cao, P. Chen, C. Miki, B. D. Fox, D. Seckel, R. Hupe, O. Banerjee, A. Connolly, K. Tatem, J. Gordon, B. Rotter, R. J. Nichol, K. Belov, M. H. Israel, S. A. Wissel, M. Stockham, B. Dailey, K. Ratzlaff, P. Dasgupta, C. Hast, P. Allison, A. G. Vieregg, A. Romero-Wolf, S. Nande, R. Young, V. Bugaev, C. Deaconu, L. Batten, P. F. Dowkontt, L. Cremonesi, J. Russell, C. Chen, P. Jain, J. Stockham, J. J. Beatty, S. Matsuno, B. F. Rauch, S. Prohira, G. S. Varner

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 O(10) microseconds, to infer the surface power reflection coefficient $\cal{R}$. The first HiCal mission (HiCal-1, Jan. 2015) yielded a sample of 100 such pairs, resulting in estimates of $\cal{R}$ at highly-glancing angles (i.e., zenith angles approaching $90^\circ$), with measured reflectivity for those events which exceeded extant calculations. The HiCal-2 experiment, flying from Dec., 2016-Jan., 2017, provided an improvement by nearly two 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. 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 2a/2b measurements.

Publisher URL: http://arxiv.org/abs/1801.08909

DOI: arXiv:1801.08909v1

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