Evaluation of CHAMP radio occultation refractivity using data assimilation office analyses and radiosondes
Poli, P. ; Ao, C.-O. ; de la Torre Juárez, M. ; Joiner, J. ; Hajj, G.-A. ; Hoff, R.-M.
Année de publication
2003
The radio occultation experiment on the CHAMP satellite has been <br>collecting observations of the Earth's atmosphere since April 2001. <br>Previous work has shown that diffraction effects not accounted for by <br>geometrical optics processing can be partially corrected by <br>back-propagation and canonical transform methods, such as implemented at<br> the Jet Propulsion Laboratory. In the present paper we evaluate the <br>bias and standard deviation of refractivity differences between Data <br>Assimilation Office global analyses and observations processed by these <br>three methods. In the tropics at 25 km altitude, the refractivity <br>biases range between ?2.5% and ?0.5% for geometrical optics, between ?1%<br> and 0.5% for back-propagation, and between ?0.5% and 1.5% for canonical<br> transform. We also assess the methods by performing one-dimensional <br>variational temperature retrievals and comparing them with close <br>radiosondes. Our final conclusion is that canonical transform is a <br>better candidate than geometrical optics and back-propagation for <br>generating GPS radio occultation datasets for data assimilation.</div>
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