The SBIR Phase I proposal outlines the approach of Night Crew Labs (NCL) in assessing the feasibility of performing GNSS radio occultations (GNSS-ROs) from a balloon platform. In Phase I, NCL will perform appropriate trade studies and sensitivity studies to identify key design requirements for the balloon-based GNSS-RO payload and the balloon platform. A lowcost, proof-of-concept GNSS-RO payload will then be designed and developed based around these requirements. Once developed, the payload will collect GNSS-RO sounding measurements from two balloon flights, and then the data will be analyzed for quality. The first, more environmentally benign demonstration flight will use a crewed hot air balloon to lift the payload to a target altitude of 5 km on a stabilized platform. The second, more ambitious demonstration flight will use an unmanned weather balloon to lift the payload to a target altitude of 30 km. After collecting GNSS-RO sounding measurements on these test flights, the measurements will be converted to bending angles and refractivity values. The data will be analyzed for quality and sensitivities to balloon parameters such as vertical altitude, balloon platform stability, and velocity. In addition, a study on using higher performance GNSS receivers and state estimation equipment will be performed.SUMMARY OF ANTICIPATED RESULTS Ground-based and in-flight GNSS measurements will be recorded and combined to achieve estimates of balloon position and velocity during the flight. In tum, these estimates will be used with raw GNSS measurements to produce bending angle and refractivity profiles from the top of the planetary boundary layer (PBL: - 2.0 km) up to the balloon altitude. Because the PBL is one of the most difficult atmospheric layers to be sensed by spacebased RO missions due to increased multipath, low signal-to-noise ratio occultations and atmospheric ducting, we will also analyze the raw GNSS-RO data within the PBL to investigate potential use.
