Development of a lunar Scintillometer for measuring ground layer turbulence

Abstract

Ground layer turbulence is one of the important site characterization parameters used for assessing the quality of an astronomical sites. Lunar Scintillometer (LuSci) is a simple, yet an effective site-testing device for measuring the ground layer turbulence. The instrument consists of a linear array of photodiodes which record the variations in moon's intensity caused by the lower layers of the Earth's atmosphere. The covariance between all possible pairs of photodiodes can be used to reconstruct the ground layer turbulence profile from the ground up to a maximum height roughly determined by the distance between the furthest pair of detectors. The 6-channel LuSci that we are developing at Indian Institute of Astrophysics is closely based on a similar instrument recently built by the team led by Andrei Tokovinin of CTIO, Chile. We intend to use this device with other site-testing instruments such as Multi Aperture Scintillation Sensor (MASS) and Differential Image Motion Monitor (DIMM), which are at different stages of development. In this work, we present the details of hardware design, signal acquisition and inversion technique used to retrieve the relevant parameters of the atmosphere. Some preliminary results from the on-site measurements and laboratory tests will also be described.