Based on the steadily growing use of mini-UAVs for numerous civilian and military applications, mini-UAVs have been recognized as an increasing potential threat. Therefore, counter-UAV solutions addressing the peculiarities of this class of UAVs have recently received a significant amount of attention. Reliable detection, localization, identification and tracking represents a fundamental prerequisite for such counter-UAV systems. In this paper, we focus on the assessment of different sensor technologies and their ability to detect mini-UAVs in a representative rural Swiss environment. We conducted a field trial in August 2015, using different, primarily short range, experimental sensor systems from armasuisse and selected research partners. After an introduction into the challenges for UAV detection in regions with strong topographic relief, we will introduce the experimental setup and describe the key results from this joint experiment.