The planetary boundary layer height (PBLH) is a key parameter for studying global land-atmosphere interactions, weather forecasting, and climate change. However, owing to the limited adaptability of existing detection techniques over complex terrain and the lack of observational consistency across different environments, unified and refined boundary layer observations on a global scale remain a major challenge. To support future spaceborne lidar missions for global boundary layer monitoring, this study establishes a closed-loop framework integrating spaceborne parameter design, theoretical simulation, and airborne experimental validation. As a core technical advance, a scaled airborne prototype was developed, and a synergistic terrain-atmosphere detection regime was introduced. By synchronously acquiring surface elevation and atmospheric backscatter signals, the system can directly retrieve the boundary layer height relative to the actual ground surface, namely above ground level (AGL), thereby fundamentally mitigating the terrain-matching bias of conventional approaches. System performance was primarily validated through the Yulin nighttime flight experiment, where the retrieved BLH showed a median difference of 10 m and a maximum RMSE of 45 m relative to the ground-based reference. The additional Hainan daytime flight experiment indicated the system's detection potential under strong background illumination and complex cloud conditions. This study validates the performance of the airborne prototype and provides empirical evidence for the parameter design of future spaceborne detection systems, supporting the construction of a globally consistent and high-precision boundary layer observation network.