Global Navigation Satellite Systems (GNSS) brought navigation to the masses. Coupled with smartphones, the blue dot in the palm of our hands has forever changed the way we interact with the world. Looking forward, cyber-physical systems such as self-driving cars and aerial mobility are pushing the limits of what localization technologies including GNSS can provide. This autonomous revolution requires a solution that supports safety-critical operation, centimeter positioning, and cybersecurity for millions of users. To meet these demands, we propose a navigation service from Low Earth Orbiting (LEO) satellites which deliver precision in-part through faster motion, higher power signals for added robustness to interference, constellation autonomous integrity monitoring for integrity, and encryption / authentication for resistance to spoofing attacks. This paradigm is enabled by the 'New Space' movement, where highly capable satellites and components are now built on assembly lines and launch costs have decreased by more than tenfold. Such a ubiquitous positioning service enables a consistent and secure standard where trustworthy information can be validated and shared, extending the electronic horizon from sensor line of sight to an entire city. This enables the situational awareness needed for true safe operation to support autonomy at scale.

Abstract. 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.

Abstract. 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 density for specific regions of interest. In contrast, in-atmosphere RO platforms can provide much higher spatial and temporal sampling of ROs around regional weather events. This study explores the capability of a low-cost and scalable commercial off-the-shelf (COTS) GNSS receiver on board 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 refractivity profiles between 6 and 19 km, with overall near-zero median difference from colocated ECMWF ERA5 reanalysis data and variability comparable to spaceborne RO missions (∼ 2.3 % median absolute deviation or MAD). Soundings from the ZPM-1 campaign show a relatively large positive refractivity bias (∼ 2.5 %). In summary, low-cost COTS RO payloads on board balloon platforms are worth further engineering and study in order to provide capabilities for dense, targeted atmospheric soundings that can improve regional weather forecasts via data assimilation.

In recent decades, GNSS Radio Occultation soundings have proven an invaluable input to global weather forecasting. The success of government-sponsored programs such as COSMIC is now complemented by commercial low-cost cubesat implementations. The result is access to more than 10,000 soundings per day and improved weather forecasting accuracy. This movement towards commercialization has been supported by several agencies, including the National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Administration (NOAA) and the U.S. Air Force (USAF) with programs such as the Commercial Weather Data Pilot (CWDP). This has resulted in further interest in commercially deploying GNSS-RO on complementary platforms. Here, we examine a so far underutilized platform: the high-altitude weather balloon. Such meteorological radiosondes are deployed twice daily at over 900 locations globally and form an essential in-situ data source as a long-standing input to weather forecasting models. Adding GNSS-RO capability to existing radiosonde platforms would greatly expand capability, allowing for persistent and local area monitoring, a feature particularly useful for hurricane and other severe weather monitoring. A prohibitive barrier to entry to this inclusion is cost and complexity as GNSS-RO traditionally requires highly specialized and sensitive equipment. This paper describes a multi-year effort to develop a low-cost and scalable approach to balloon GNSS-RO based on Commercial-Off-The-Shelf (COTS) GNSS receivers. We present hardware prototypes and data processing techniques which demonstrate the technical feasibility of the approach through results from several flight testing campaigns.

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