Ultra-high energy cosmic rays produce extensive air showers of secondary particles upon entering the atmosphere. Sampling the footprint of these particles with surface detectors is a widely used detection technique. In this data set, the reconstruction of cosmic-ray properties like the shower maximum using the measured particle footprint can be investigated. The Observatory features 9 x 9 stations arranged in a Cartesian grid with a spacing of 1500 m. Each station can measure the time-dependent signals in a window of 80 bins a 25 ns. The data were simulated using a modified version of https://git.rwth-aachen.de/DavidWalz/airshower and used in https://arxiv.org/abs/2107.00656.