Ground-layer turbulence profiling using a lunar SHABAR

Abstract

Profiling the ground layer turbulence for daytime seeing applications using an array of photodiodes has been documented in literature, in particular by Beckers who coined the term "SHABAR" for the instrument, short for Shadow Band Ranger. In this case the photodiodes measure the variation of solar intensity as a function of time and the correlation of scintillation between spatially separated scintillometers can be used to derive structure constant values for the lower 100m or so. More recently SHABARs have been applied to night time atmospheric profiling using the moon as the extended source, such as the Pan-STARRS lunar SHABAR, a more challenging venture given the lower structure constant values and therefore higher sensitivity required. We present a summary of the lunar SHABAR currently operating at the Antarctic site of Dome C, one of the three Gattini site testing instruments for the Italian-led IRAIT project. The SHABAR was designed with low noise performance in mind and for low temperature operation. Ground layer profiling is of particular importance at the Dome C site during winter-time as it is known the majority of the integrated seeing measured at ground level is created in a turbulent layer very close to the ground.