Open AccessGPS radio occultations with CHAMP: A radio holographic analysis of GPS signal propagation in the troposphere and surface reflections
Author(s) -
Beyerle G.,
Hocke K.,
Wickert J.,
Schmidt T.,
Marquardt C.,
Reigber C.
Publication year - 2002
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd001402
Subject(s) - radio occultation , occultation , global positioning system , troposphere , radio wave , geology , radio propagation , multipath propagation , gps signals , reflection (computer programming) , geodesy , elevation (ballistics) , ray tracing (physics) , remote sensing , physics , environmental science , ionosphere , geophysics , optics , assisted gps , atmospheric sciences , astronomy , telecommunications , statistics , mathematics , quantum mechanics , estimator , computer science , programming language
Within the first nine months following the activation of the GPS radio occultation experiment aboard the low Earth orbiting satellite CHAMP, more than 25,000 occultation events have been observed. A radio holographic analysis of 3783 occultation events, recorded between 14 May 2001 and 10 June 2001, reveals that in about 20–30% of these events the received signal contains contributions from components reflected at Earth's surface. On the basis of geometrical ray tracing and multiple phase screen calculations, characteristic frequency shifts in the radio holograms' power spectral densities are analyzed quantitatively. These frequency shifts are found to be dominated by surface elevation at the reflection point location and ground‐level refractivity. Using temperature and pressure profiles from European Centre for Medium‐Range Weather Forecasting (ECMWF) analyses, ground‐level specific humidities are derived in good agreement with ECMWF values. Complex patterns found in radio hologram spectra within a subset of observations at low latitudes are interpreted in terms of multipath propagation caused by layered structures in the refractivity field.