HR: 08:30h
AN: A51F-03 INVITED     [Abstracts]
TI: Inversion of SAC-C Open-Loop Radio Occultation Signals at UCAR
AU: * Sokolovskiy, S
EM: sergey@ucar.edu
AF: University Corporation for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307-3000 United States
AU: Rocken, C
A51F-03 AF: University Corporation for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307-3000 United States
AU: Hunt, D
A51F-03 AF: University Corporation for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307-3000 United States
AU: Schreiner, W
A51F-03 AF: University Corporation for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307-3000 United States
AU: Johnson, J
A51F-03 AF: University Corporation for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307-3000 United States
AU: Masters, D
A51F-03 AF: University of Colorado, 431 UCB, Boulder, CO 80309-0431 United States
AU: Esterhuizen, S
A51F-03 AF: University of Colorado, 431 UCB, Boulder, CO 80309-0431 United States
AB: In open loop (OL) mode, a radio occultation (RO) receiver produces complex samples in excess of a phase (Doppler) model generated in the receiver without feedback from the signal. The complex samples contain the atmospheric modulation (AM) of the amplitude and phase and the navigation data modulation (DM) of the phase. Inversion of the OL signals requires removal of the DM and extraction and connection of the phase between samples (both these operations are performed in a receiver running in phase locked loop (PLL) mode). In OL post-processing, removal of the DM and connection of the phase is done by additional frequency shifting of the recorded complex signal with a more accurate model than that used in the receiver. In preparation for the COSMIC mission, Jet Propulsion Laboratory (JPL) operated the SAC-C RO receiver in the OL test mode during certain time periods in 2005. JPL provided some OL data to the COSMIC Data Analysis and Archive Center (CDAAC) at UCAR. For high- and mid-latitude occultations the DM is well distinguished and removed from the background of the AM. For some tropical occultations, due to large AM, the DM cannot be distinguished and correctly removed without the use of an externally recorded DM bit sequence. For some occultations the DM bit sequences were collected by a ground-based receiver at Boulder CO and used for inversions of the SAC-C OL RO signals. Currently, CDAAC is deploying a network of ground-based receivers for collecting DM bit sequences for COSMIC. Comparisons of the OL- and PLL-inverted refractivity profiles with ECMWF global analysis show that OL results in significantly better penetration (50% below 1km) than PLL (50% below 4-6km). Also, OL results in substantially smaller negative refractivity bias than PLL in the tropical lower troposphere. It is believed that the remaining bias is caused mainly by propagation effects. The algorithms and software developed at CDAAC during processing of the SAC-C OL test data will be used for COSMIC mission.
UR: http://www.cosmic.ucar.edu
DE: 3360 Remote sensing
DE: 3394 Instruments and techniques
DE: 6964 Radio wave propagation
DE: 6969 Remote sensing
DE: 6974 Signal processing (0674)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005