Combining the High Altitude Lidar Observatory (HALO) and Scanning High-Resolution Interferometer Sounder (S-HIS) for Thermodynamic Retrievals during the EcoDemonstrator Campaign

Hyperspectral infrared (IR) sounders, such as the Cross-track Infrared Sounder (CrIS), provide radiance measurements that are a critical source of temperature and water vapor sounding information within the Earth observing system. However, as noted by the 2017 Decadal Survey, these instruments have a limited sensitivity to the planetary boundary layer (PBL), resulting in inadequate estimates of temperature and water vapor within the PBL. Water vapor differential absorption lidars (DIAL) can provide water vapor retrievals at very high vertical resolution and low uncertainty but have yet to be demonstrated in space. The NASA PBL Study Team Report identified IR sounders and water vapor lidars as two essential components to a future space-based observing system designed to improve soundings of the PBL.

In addition to the broad weighting functions limiting the information content of space-based sounders, radiance measurements in many spectral regions are dependent upon both temperature and water vapor. While a DIAL would clearly improve water vapor retrievals, constraining the water vapor results will also improve the temperature retrieval from the IR sounder. This result has been demonstrated from a ground-based perspective in Turner and Löhnert (2021). This presentation will extend those results with a focus on a downward looking perspective for this type of synergy. The High Altitude Lidar Observatory (HALO) and Scanning High-resolution Infrared Sounder (S-HIS) have been successfully demonstrated to provide high quality observations on from airborne platforms. HALO and S-HIS observations from the same aircraft would provide a dataset that would simulate a space-based observing system with a water vapor DIAL and IR sounder. These instruments are set to fly together as part of NASA’s EcoDemonstrator mission over the Pacific Northwest United States in October of 2023. Synthetic information content analyses will quantify the improved degrees of freedom and retrieval uncertainties for a synergy of these two sensors, compared to either sensor operating individually. Furthermore, preliminary observations from the S-HIS and HALO as part of the EcoDemonstrator campaign will be presented.