Abstract
Abstract. Airborne differential absorption lidar (DIAL) offers a uniquely capable solution to the problem of measuring water vapor (WV) with high precision, accuracy, and resolution throughout the troposphere and lower stratosphere. The High Altitude Lidar Observatory (HALO) airborne WV DIAL was recently developed at NASA Langley Research Center and was first deployed in 2019. It uses four wavelengths near 935 nm to achieve sensitivity over a wide dynamic range and simultaneously employs 1064 nm backscatter and 532 nm high-spectral-resolution lidar (HSRL) measurements for aerosol and cloud profiling. A key component of the WV retrieval framework is flexibly trading resolution for precision to achieve optimal datasets for scientific objectives across scales. An approach to retrieving WV in the lowest few hundred meters of the atmosphere using the strong surface return signal is also presented. The five maiden flights of the HALO WV DIAL spanned the tropics through midlatitudes with a wide range of atmospheric conditions, but opportunities for validation were sparse. Comparisons to dropsonde WV profiles were qualitatively in good agreement, though statistical analysis was impossible due to systematic error in the dropsonde measurements. Comparison of HALO to in situ WV measurements aboard the aircraft showed no substantial bias across 3 orders of magnitude, despite variance (R2=0.66) that may be largely attributed to spatiotemporal variability. Precipitable water vapor measurements from the spaceborne sounders AIRS and IASI compared very well to HALO with R2>0.96 over ocean.
Highlights
Water vapor (WV) is a key component of the Earth’s atmosphere and water cycle, playing major roles in cloud, weather, and climate processes, including radiative balance as the most dominant greenhouse gas (Trenberth et al, 2007)
This paper provides an overview of implementation and retrieval methodology for the new High Altitude Lidar Observatory (HALO) airborne WV differential absorption lidar (DIAL) system and comparison to other instrumentation from its five maiden flights, serving to inform the community of a new capability within the suborbital portfolio
The HALO instrument and WV retrieval were designed based on decades of legacy of related DIAL efforts at NASA Langley Research Center (LaRC) and in the global community
Summary
Water vapor (WV) is a key component of the Earth’s atmosphere and water cycle, playing major roles in cloud, weather, and climate processes, including radiative balance as the most dominant greenhouse gas (Trenberth et al, 2007). Spaceborne passive sounders have the great advantage of daily global coverage, and their column and cloud products are important contributors to operational forecasting and climate research (Wulfmeyer et al, 2015). Their WV retrieval vertical resolution is roughly 1–2 km at best in the troposphere, and accuracy is closely tied to the observed scene as well as the prior inputs to the retrievals. Raman lidar systems provide the advantageous capability of monitoring multiple gas species simultaneously, but this comes at the cost of requiring large, high-peak-power ultraviolet lasers to overcome small Raman scattering cross sections, as well as a need for frequent calibration.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
