Advancing In-Atmosphere GNSS Radio Occultation for Supplemental Observations and Improved Data Assimilation Aboard Multiple Observing Platforms

Spaceborne GNSS radio occultation (RO) soundings have long demonstrated a large positive impact on global weather and climate monitoring and prediction by providing high vertical resolution thermodynamic profiles under all weather conditions. In addition, the RO profiling from in-atmosphere platforms such as airplanes and high-altitude balloons has attracted much more attention in recent years. In-atmosphere RO can offer unprecedented temporal and spatial sampling density over targeted regions of interest. Here we detail results from two in-atmosphere GNSS RO platforms that were tested across multiple years.

First, we show results from a balloon-borne RO (BRO) platform comprised of parts that are all available commercial off-the-shelf (COTS). A highly-compact, low-cost GNSS receiver developed by the Night Crew Labs (NCL) was successfully deployed on several airplane and high-altitude balloon platforms for testing. The bending angle and refractivity retrievals from two balloon flight campaigns (e.g., World View and ZPM-1) are analyzed and compared to the colocated ERA5 global reanalysis. BRO results indicate that the COTS platform can observe atmospheric refractivity through radio occultation compared to colocated ERA5 with near-zero median refractivity difference when platform yaw control is present, and within ~3% when platform control is absent.

Second, we show results from a series of airborne (ARO) flights using the positioning technology installed on various Airbus aircraft. RO cases extracted from Airbus flights across Europe and the Middle East from 2017 to 2019 are processed. The ARO refractivity retrievals show overall near-zero median difference in the middle troposphere. Therefore, ARO soundings from commercial flights have the capacity to drastically improve the number and quality of observations in the atmosphere, particularly over areas with sparse in-situ observations. In the future, in-atmosphere COTS RO payloads are worth further improvement for dense regional atmospheric soundings. Additionally, the acquisition and application of ARO profiles akin to upper-air data from commercial aircraft will likely improve regional and global weather forecasts.