Title: 
 FORMOSAT-3/COSMIC POD Data Processing and Initial Results
 
Authors: 
 Tang, C. 

Affiliation: 
 AA(; p6888102@ccmail.ncku.edu.tw) 

Publication: 
 American Geophysical Union, Fall Meeting 2006, abstract #A21B-0833 

Publication Date: 
 12/2006 

Origin: 
 AGU 

AGU Keywords: 
 1220 Atmosphere monitoring with geodetic techniques (6952), 1225 Global change from geodesy (1222, 1622, 1630, 1641, 1645, 4556) 

Abstract Copyright: 
 (c) 2006: American Geophysical Union 

Bibliographic Code: 
 2006AGUFM.A21B0833T 

Abstract
The six satellites of the collaborative Taiwan-U.S. FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) space program were successfully launched from Vandenberg, U.S.A. on April 15, 2006. As of September 7, 2006, one satellite (FM5) has already been transferred to the 800-km final orbit, while the other five satellites (FM1-4 and FM6) are currently waiting in the ~520-km parking orbit for subsequent orbit raising deployment. There are two GPS antennas with different orientation onboard each satellite whose measurements are used specifically for precise orbit determination (POD). The received GPS signals by the POD antennas were rather sparse and unstable in the initial 5 weeks. Since then, the available GPS measurements have gradually increased from 10-20% in the early stage to almost 90% in 11 weeks after the launch. For the two POD antennas (POD+X and POD-X), one antenna can perform normally and record observations from up to 9 GPS satellites in view; however, the other antenna is programmed to track up to 4 GPS satellites due to onboard memory limitation. For this reason, we first performed orbit computation using zero-difference GPS phases collected by the normal antenna. For each day's orbit computation, we designed a 6-hr (25%) overlap for inner orbital accuracy assessment, and overlap analysis shows that the achievable 3D RMS was around 19 cm, or 11 cm per axis. In a separate effort, orbit computation based on the lesser antenna was also performed. The orbital difference between the results obtained from the two antennas was significant, with a 3D RMS value of 64 cm. The early results indicate that more work is needed in order to incorporate GPS data from both antennas into a unified solution.