Airborne Lidar Observations of Water Vapor Profiles and Planetary Boundary Layer Heights—Prospects for Future SmallSat Missions

Water vapor is the most dominant short-lived greenhouse gas in the atmosphere and plays a key role in many atmospheric processes critical to driving Earth’s weather and climate systems. Recently, the National Research Council identified accurate and high vertical resolution measurements of water vapor profiles in the planetary boundary layer as a most important target observable in the 2017 report on Earth Science Applications from Space (ESAS). NASA Langley Research Center has developed the High Altitude Lidar Observatory (HALO) lidar system to address the observational needs of NASA’s weather, climate, carbon cycle, and atmospheric composition focus areas. HALO is a compact and module lidar designed as an airborne simulator for future space-based greenhouse gas differential absorption lidar (DIAL) missions called out by the 2017 ESAS and also serves as testbed for risk reduction of key technologies required to enable those missions. To respond to a wide range of airborne process studies, HALO can be rapidly reconfigured to provide either, H₂O DIAL+HSRL, CH₄ DIAL+HSRL, or CH₄ DIAL+H₂O DIAL measurements using three different laser transmitters and a single multi-channel and multi-wavelength receiver. This paper will provide an overview of the HALO instrument including emerging transmitter and receiver technologies that allow for operation on high altitude aircraft as well a future affordable SmallSat platforms. We will present results from three recent airborne field campaigns demonstrating HALO’s water vapor profiling capabilities as well as methane column and aerosol/cloud profiling capabilities that are also identified as most important targeted observables in the 2017 ESAS. We will conclude with an outlook on a future cross-cutting DIAL mission concept adapted from the HALO airborne simulator that should be capable of rideshare launch on an Evolved Expendable Launch Vehicle Secondary Payload Adapter (ESPA), drastically reducing mission costs over a dedicated launch vehicle.