Atmospheric Radio Occultation Observation from Spire CubeSat Nanosatellites

The Radio Occultation (RO) technique is based on the atmospheric bending of radio waves transmitted by GPS satellites. Measurement of the bending angle allows one to retrieve the air refractivity, which depends on air temperature and water vapor. The occultation observations provide high vertical resolution and don’t require calibration. Previous missions have demonstrated the high value of RO data for numerical weather models.

Spire Global Inc. is the first commercial company to obtain high-quality RO data from GPS receivers onboard nanosatellites. A high-gain antenna and software receiver allowed us to implement open-loop tracking of RO signals. The open-loop tracking technique is critical for deep penetration into the atmosphere and the ability to observe both rising and setting occultations. We also developed state-of-art software for precise orbit determination and RO data processing.

From late March to the end of April 2017 we delivered RO profiles to NOAA in accordance with the Commercial Weather Data Pilot program. The profiles were retrieved by the Spire Processing Center. Our estimate shows that the quality of raw data, precise orbit determination, and atmospheric temperature retrieval are comparable with those of the COSMIC program.

We present an outline of the Spire RO program, the latest results of our atmospheric profiling, and a statistical comparison with the GFS model. We demonstrate the potential of using a constellation low Earth orbiting 3U CubeSat satellites for the observation of radio occultations. We believe that commercially available, high-quality real-time RO data are critical for improving global and regional weather models.