Water vapor, a minor constituent of the earth's atmosphere, plays a major role in the radiation budget and the water cycle with important implications for weather and climate. Due to the heterogeneous distribution of its sources, evaporation, and sinks, condensation and precipitation, and due to the complexity of atmospheric motion and mixing, its distribution in the atmosphere is highly variable. Despite the high relevance of this trace gas, its variability challenges accurate measurements of its concentration. Advanced airborne lidar instruments aid to better observe water vapor and its transport in the atmosphere, in view of an improved understanding of atmospheric processes that are key to weather and climate research. The combination of a water vapor differential absorption lidar and a heterodyne detection Doppler wind lidar on an aircraft is new and allows to measure vertical profiles of the latent heat flux in a convective boundary layer and to portray the small- to large-scale humidity transport and variability along the aircraft flight track with high accuracy and spatial resolution.