  Hybrid Reconfigurable Intelligent Surfaces (HRISs), which are capable of
simultaneous programmable reflections and sensing, are expected to play a
significant role in future wireless networks, enabling various Integrated
Sensing and Communication (ISAC) applications. In this paper, we focus on
HRIS-enabled Unmanned Aerial Vehicle (UAV) networks and design the HRIS
parameters (phase profile, reception combining, and the power splitting between
the two functionalities) for jointly estimating the individual UAV-HRIS and
HRIS-base-station channels as well as the Angle of Arrival (AoA) of the
Line-of-Sight (LoS) component of the UAV-HRIS channel. We derive the Cram\'er
Rao lower bounds for the estimated channels and evaluate the performance of the
proposed approach in terms of the channel estimation error and the LoS AoA
estimation accuracy, verifying its effectiveness for HRIS-enabled ground-to-UAV
wireless communication systems.
