The High Altitude Lidar Observatory (HALO) is an active remote, airborne lidar developed by NASA Langley Research Center. HALO operates across 4 wavelengths (1645, 1064, 935, 532 nm) and uses a combination of Differential Absorption Lidar (DIAL) and High Spectral Resolution Lidar (HSRL) methods to measure lidar backscatter and depolarization ratio. It provides vertical profiles of aerosol and cloud optical properties, atmospheric water vapor, and methane at a data rate of 2 Hz. HALO has a nominal spatial resolution of 12 km horizontally and 315 m vertically at an altitude of 10 km.