Retrieval of Atmosphere Humidity Profiles from GNSS Radio Occultation Observations

Paper number

IAC-16,B1,IP,31,x33889

Coauthor

Dr. Francesco Vespe, Agenzia Spaziale Italiana (ASI), Italy

Year

2016

Abstract

The huge amount of GPS Radio Occultation (RO) observations currently available thanks to space mission like COSMIC, CHAMP, GRACE, TERRASAR-X etc., have greatly encouraged the research of new algorithms suitable to extract humidity, temperature and pressure profiles of the atmosphere in a more and more precise way. For what concern the humidity profiles in these last years two different approaches have been widely proved and applied: the “Simple” and the 1DVAR methods. The Simple methods essentially determine dry refractivity profiles from temperature analysis profiles and hydrostatic equation. Then the dry refractivity is subtracted from RO refractivity to achieve the wet component. Finally from the wet refractivity is achieved humidity. 
The 1DVAR approach combines RO observations with profiles given by the background models with both the terms weighted with the inverse of covariance matrix. The advantage of “Simple” methods is that they are not affected by bias due to the background models.
We have proposed in the past an our  approach to retrieve humidity. Our approach can be classified among the “Simple” methods. Our approach works with dry atmospheric CIRA-Q models which depend on latitude, DoY and height. The dry CIRA-Q refractivity profile is selected estimating the involved parameters in a non linear least square fashion achieved by fitting RO observed bending angles through the stratosphere. our approach as well as all the other “Simple” methods, has as drawback the unphysical occurrence of negative “humidity”. Thus we propose to apply a weighting strategy based on the residuals of the fit just to minimize the effects of this inconvenient. After a proper tuning of the approach, we plan to present the results of the validation.

Abstract document

IAC-16,B1,IP,31,x33889.brief.pdf

Manuscript document

IAC-16,B1,IP,31,x33889.pdf (🔒 authorized access only).

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