OSSE capability for GNSS RadioOccultation RO observations Lidia
OSSE capability for GNSS Radio-Occultation (RO) observations Lidia Cucurull JCSDA
Introduction n n There are several options for a COSMIC follow-on mission (different orbit configuration, number of satellites, etc) What is the optimal “choice”? CEOS action WE-07 -03 on ‘evaluation of the requirements to conduct RO OSSEs’ The action has recently been completed – International Joint OSSE project – 2 -yr full time post-doctoral scientist n Hopefully, we will get funding soon
Radio Occultation concept An occultation occurs when a GPS (GNSS) satellite rises or sets across the limb wrt to a LEO satellite. n A ray passing through the atmosphere is refracted due to the vertical gradient of refractivity (density). n During an occultation (~ 3 min) the ray path slices through the atmosphere n Occulting GPS Ionosphere Neutral atmosphere LEO Earth Raw measurement: change of the delay (phase) of the signal path between the GPS and LEO during the occultation. (It includes the effect of the atmosphere). GPS transmits at two different frequencies: ~1. 6 GHz (L 1) and ~1. 3 GHz (L 2).
Choice of RO products Raw measurements of phase of the two signals (L 1 and L 2) s 1, s 2, Bending angles of L 1 and L 2 a 1, a 2 (neutral) bending angle Clocks correction, orbits determination, geometric delay a Ionospheric correction Abel transfrom Refractivity N Hydrostatic equilibrium, eq of state, apriori information Atmospheric products T, Pw, P
Requirements for RO OSSE n n n Build the interface between the chosen RO simulator and the Nature Run Choose the RO products to be simulated Simulate the observations and tune the error covariance matrix for the selected constellations Conduct the assimilation experiments Evaluate the results Choose the ‘optimal’ constellation
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