Aircraft avoidance for laser propagation at the Large Binocular Telescope Observatory: life under a busy airspace

A key aspect of LGS operations is the implementation of measures to prevent the illumination of airplanes flying overhead. The most basic one is the use of “aircraft spotters” in permanent communication with the laser operator. Although this is the default method accepted by the FAA to authorize laser propagation, it relies on the inherent subjectivity of human perception, and requires keeping a small army of spotters to cover all the nights scheduled for propagation. Following the successful experience of other observatories (Keck and APO), we have installed an automatic aircraft detection system developed at UCSD known as TBAD (Transponder-Based Aircraft Detection). The system has been in continuous operation since April 2015, collecting detection data every night the telescope is open. We present a description of our system implementation and operational procedures. We also describe and discuss the analysis of the TBAD detection data, that shows how busy our airspace is, and the expected impact on the operation efficiency of the observatory.