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

• Main Authors: Prohira, S., Novikov, A., Dasgupta, P., Jain, P., Nande, S., Allison, P., Banerjee, O., Batten, L., Beatty, J. J., Belov, K., Besson, D. Z., Binns, W. R., Bugaev, V., Cao, P., Chen, C., Chen, P., Clem, J. M., Connolly, A., Cremonesi, L., Dailey, B., Deaconu, C., Dowkontt, P. F., Fox, B. D., Gordon, J., Gorham, P. W., Hast, C., Hill, B., Hupe, R., Israel, M. H., Lam, J., Liu, T. C., Ludwig, A., Matsuno, S., Miki, C., Mottram, M., Mulrey, K., Nam, J., Nichol, R. J., Oberla, E., Ratzlaff, K., Rauch, B. F., Romero-Wolf, A., Rotter, B., Russell, J., Saltzberg, D., Seckel, D., Schoorlemmer, H., Stafford, S., Stockham, J., Stockham, M., Strutt, B., Tatem, K., Varner, G. S., Vieregg, A. G., Wissel, S. A., Wu, F., Young, R.
• Format: Text
• Language: unknown
• Published: arXiv 2018
• Subjects: Instrumentation and Methods for Astrophysics astro-ph.IM; FOS Physical sciences; Antarctic; The Antarctic; Antarc*
• Online Access: https://dx.doi.org/10.48550/arxiv.1801.08909; https://arxiv.org/abs/1801.08909

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. : submitted to Astropart. Phys