ROSA: The Italian Space Agency GPS Radio Occultation Receiver. Signal Tracking Characteristics and Terrestrial Measurement Campaign

In the framework of an Italian Space Agency (ASI) contract, Alenia Spazio — Laben developed a new GPS radio occultation receiver: the ROSA receiver. It will manage both “rise” and “set” occultation events, tracking signals coming from the stratosphere in closed-loop and switching to the open-loop when they emerge from the troposphere. It is well known that the open-loop signal tracking needs a good Excess-Doppler prediction, and that it has to be evaluated in advance (and in quasi real time) by the occultation on-board software. The adopted prediction strategy is a simplified and optimized version of the technique suggested by Sokolovskiy (2001). This work provides the results of the validation of this technique, carried on through comparisons with about 200 Excess-Doppler observations collected by the CHAMP Radio Occultation GPS receiver during the winter season 2002/2003 above Europe. Some insights about the prediction of the end occultation time for setting events (or start occultation time for rising events) are also given. The strategy implemented by the on-board ROSA occultation manager for the open-loop tracking is quickly introduced. Also a mountain top measurement campaign with the ROSA breadboard receiver is discussed. It is planned for 2006. This experiment is encouraged by ASI in order to test and to validate the ROSA tracking capabilities and the algorithms necessary for the extraction of the GPS occultation observables from raw data.

[1]  Sergey Sokolovskiy,et al.  Tracking tropospheric radio occultation signals from low Earth orbit , 2001 .

[2]  M. E. Gorbunov,et al.  Canonical transform method for processing radio occultation data in the lower troposphere , 2002 .

[3]  A. Zin,et al.  On the prediction of the Excess-Doppler evolution for the bandwidth optimization of the LAGRANGE RO receiver , 2003 .

[4]  H. H. Benzon,et al.  Full Spectrum Inversion of radio occultation signals , 2003 .

[5]  W. G. Melbourne,et al.  The application of spaceborne GPS to atmospheric limb sounding and global change monitoring , 1994 .

[6]  Anthony J. Mannucci,et al.  Lower troposphere refractivity bias in GPS occultation retrievals , 2003 .

[7]  Steven Businger,et al.  GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results , 1996 .

[8]  P. Crosta,et al.  Gnss Radio Occultation From Leo: Occultation Management And Open-Loop Tracking Aspects , 2004 .

[9]  Gottfried Kirchengast,et al.  Occultations for Probing Atmosphere and Climate , 2004 .

[10]  J. Wickert,et al.  Atmospheric sounding by global navigation satellite system radio occultation: An analysis of the negative refractivity bias using CHAMP observations , 2004 .

[11]  W. Bertiger,et al.  A technical description of atmospheric sounding by GPS occultation , 2002 .

[12]  S. Sokolovskiy.  Open Loop Tracking and Inverting GPS Radio Occultation Signals: Simulation Study , 2004 .

[13]  Ernest K. Smith,et al.  The Constants in the Equation for Atmospheric Refractive Index at Radio Frequencies , 1953, Proceedings of the IRE.