  Communication infrastructure is often severely disrupted in post-disaster
areas, which interrupts communications and impedes rescue. Recently, the
technology of reconfigurable intelligent surface (RIS)-equipped-UAV has been
investigated as a feasible approach to assist communication under such
conditions. However, the channel characteristics in the post-disaster area
rapidly change due to the topographical changes caused by secondary disasters
and the high mobility of UAVs. In this paper we develop a new fading-shadowing
model to fit the path loss caused by the debris. Following this, we derive the
exact distribution of the new channel statistics for a small number of RIS
elements and the approximate distribution for a large number of RIS elements,
respectively. Then, we derive the closed-form expressions for performance
analysis, including average capacity (AC), energy efficiency (EE), and outage
probability (OP). Based on the above analytical derivations, we maximize the
energy efficiency by optimizing the number of RIS elements and the coverage
area by optimizing the altitude of the RIS-equipped UAV, respectively. Finally,
simulation results validate the accuracy of derived expressions and show
insights related to the optimal number of RIS elements and the optimal UAV
altitude for emergency wireless communication (EWC).
