Understanding the Performance of Radio Occultation Weather Observations

Weather forecasters have come to rely on Global Navigation Satellite System (GNSS) radio occultation (RO) data to improve and calibrate data inputs to weather prediction models used for daily forecasts. GNSS RO technology has improved greatly since its initial inception two decades ago, a heritage which continues to mature. NOAA is preparing for a second generation RO system, COSMIC-2, while commercial vendors are now entering the market offering solutions using CubeSat-form satellites, with the potential for per-RO cost reductions due to economies of scale, as multi-satellite constellations are established. These developments raise questions of tradeoffs between cost and quality. This paper identifies a number of the technical factors that contribute to the value of RO data. Clarifying these factors will encourage further research leading to a deeper understanding of the value of RO observations using both current and future technology and eventually leading to superior system design, signal processing and assimilation.

Since RO was first demonstrated on GPS/MET in 1995, significant strides have been made in understanding the technology and enabling more useful occultation data. However, underlying questions that guide system design are still unresolved. The RO scientific community has identified challenges including data quantity; occultation quality; spatial distribution; and data latency. This paper presents quality questions that need to be further explored. For example, the assumption that more RO data is always better is overly simplistic. Assessment of the value of each RO system must consider data quantity; occultation quality; spatial distribution; and data latency factors. Each consideration is reviewed in this paper, hoping to improve the quality of the conversations regarding RO data so that all participants can more fully grasp what really matters to the forecaster. This paper is in support of NOAA’s objective to promote research to improve National Weather Service operations, and likewise fulfill the cycle of operations to research.