The Value of Research Satellites in Contributing to the Climate Record Established by GNSS Radio Occultation

The first operational weather constellation based on the radio occultation (RO) technique is planned for launch in 2017, using signals transmitted by the Global Navigation Satellite Systems (GNSS) GPS and GLONASS. While this new FORMOSAT-7/COSMIC-2 mission is expected to improve upon the successes originally established by FORMOSAT-3/COSMIC (a demonstration constellation launched in 2006) and MetOp-A (the first operational RO satellite, also since 2006), it is not widely appreciated that a variety of research satellites besides COSMIC routinely contribute data to operational weather forecasts. These same satellites have established a heritage of providing information for observing long-term climate change, despite their heterogeneous implementations. In this talk, we discuss the numerous contributions made by research satellites to climate science, focusing primarily on missions carrying NASA-designed RO receivers. Value accrues from increased global sampling, increased continuity or time span of data, and establishing upper limits to instrumental bias by comparing retrieved geophysical quantities from diverse instruments and platforms. Whereas value to numerical weather prediction (NWP) is best achieved by an uninterrupted operational “backbone” RO constellation providing more than 20,000 globally distributed profiles daily, research satellites play a critical role in climate research, and augment NWP in proportion to the additional number of observations they provide. We will show how a diversity of RO missions has contributed to observing long-term climate change and to understanding climate processes. We will suggest ways that RO research satellites can continue to provide significant value as this new era of operational RO constellations is about to begin.