The non-stationarity of the atmospheric boundary layer (ABL) limits the usefulness of static lidar systems in measuring the ABL height. To address this issue, the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE), a scanning aerosol backscatter lidar, was used to spatially sample the atmosphere during the International H2O Project (IHOP). The boundary-layer height is estimated from HARLIE backscatter data using an automated algorithm based on a Haar wavelet transformation. A comparison of the algorithm output with radiosonde- and model-derived boundary-layer heights reveals good agreement between the methods, thus validating the algorithm. Spatial sampling also yields the spatial variability of the boundary-layer height and a case study is used to illustrate the benefits of this spatial variability measurement.