GNSS radio occultation soundings from commercial off-the-shelf receivers onboard balloon platforms

The Global Navigation Satellite System (GNSS) radio occultation (RO) technique has proven to be an effective tool for Earth atmosphere profiling. Traditional spaceborne RO satellite constellations are expensive with relatively low sampling rates for individual satellites. Airborne RO platforms can provide much higher spatial and temporal sampling of ROs around regional weather events. This paper explores the capability of a low-cost and scalable Commercial-Off-The-Shelf (COTS) GNSS receiver onboard high-altitude balloons. The refractivity retrievals from balloon-borne RO payloads obtained from two flight campaigns (World View and ZPM-1) are presented. The balloon-borne RO soundings from the World View campaign show high-quality refractivity profiles in the troposphere with near-zero median difference (~2.3% median-absolute-deviation) from the colocated ECMWF ERA5 reanalysis data. Soundings from the ZPM-1 campaign show a relatively large positive bias (~2.5%). In summary, the low-cost COTS RO payloads onboard balloon platforms are worth further improvement for dense targeted atmospheric soundings to improve regional weather forecasts.