Improvements to MASS turbulence profile estimation at Paranal

摘要

The multi-aperture scintillation sensor (MASS) is a widely-used robotic turbulence profiling instrument that measures the turbulence strength in 6 altitude resolution elements centered at 0.5, 1, 2, 4, 8 and 16 km. Paranal Observatory has a facility MASS instrument that is used to support adaptive optics operations. The observatory also has a stereo scintillation detection and ranging (S-SCIDAR) instrument that is typically operated for several nights per month, measuring the full turbulence profile with a resolution of several hundred metres. We make a comparison between concurrent S-SCIDAR and MASS measurements by binning the S-SCIDAR profiles according to the MASS response functions and performing a layer-by-layer comparison of the 6 MASS layers. We show that some layers tend to be significantly over- or underestimated by MASS, compared to S-SCIDAR, but the sum of all 6 layers is quite consistent between the two instruments. We present a detailed Monte Carlo simulation of the MASS instrument, using S-SCIDAR profiles as inputs to reproduce realistic MASS output raw data. By comparing simulated raw data with real measurements we verify the physical operation of the MASS instrument and validate the simulation code as a tool to investigate the profile restoration problem.