OSSE capability for GNSS Radio-Occultation (RO) observations

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OSSE capability for GNSS Radio-Occultation (RO)
observations

• Lidia Cucurull
• JCSDA

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Introduction

• 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
• Hopefully, we will get funding soon

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Radio Occultation concept

• An occultation occurs when a GPS (GNSS)
  satellite rises or sets across the limb wrt to a
  LEO satellite.
• A ray passing through the atmosphere is
  refracted due to the vertical gradient of
  refractivity (density).
• During an occultation ( 3min) the ray path
  slices through the atmosphere

• 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 (L1) and 1.3 GHz (L2).

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Choice of RO products
Raw measurements of phase of the two signals (L1
and L2)
s1, s2,
Bending angles of L1 and L2
a1, a2
(neutral) bending angle
Clocks correction, orbits determination,
geometric delay
Refractivity
a
Ionospheric correction
Atmospheric products
N
Abel transfrom
T, Pw, P
Hydrostatic equilibrium, eq of state, apriori
information
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Requirements for RO OSSE

• 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