Urban canyon environments block all sensor modalities for drones flying between buildings

In dense urban environments, drones flying at 10-30m altitude between buildings are masked by structural clutter creating radar multipath reflections, obscured from electro-optical sensors by building shadows, and hidden from acoustic sensors by ambient city noise at 60-80 dB. A drone flying down a city street at rooftop level is effectively invisible until it clears the last building, leaving under 10 seconds for detection-to-engagement. This persists because all C-UAS sensor suites were developed and tested in open-field environments with clear line-of-sight -- urban environments violate every assumption in the sensor design.