GPS Orbits Jim Rohde Bob Dulaney Bill Kass

GPS Orbits Jim Rohde, Bob Dulaney, Bill Kass, Steve Hilla National Geodetic Survey 2005 Convocation October 24 -28, 2005 Silver Spring, Maryland Holiday Inn 8777 Georgia Avenue

Improvements to Orbit Processing in 2004/2005 • Stars Procedure – Added redundant baselines by processing sub-networks and combining their normal equations • Integer phase ambiguity fixing • Moved production from HP to SUN x 86 platform • Orbit adjustment done more rigorously (ADJEPH) • Fixed pole tide sign error • Improved sub-daily EOP model • Absolute Antenna Phase Center Offsets and PCVs • Monuments as Reference Points (future) • Updated Ocean Tide Loading Model (future)

Multiyear CORS • Motivation – To provide long-term consistent solution of all data – Results used for CORS coordinates and velocities – realization of NSRS – Implement recent improvements in GPS Data Processing • Time Span – 1994 through 2005 • Reference Frame IGb 00 – IGS realization of ITRF 00

Multiyear CORS (cont. ) • Procedure – Streamline processing to fit with routine operations and avoid repeated reprocessing – Step 1: Daily Global Solution – orbits, EOPs, IGS and some CORS site positions; solutions stacked weekly for the IGS – Step 2: Daily CORS Solution – CORS and some North American IGS site positions; solutions stacked weekly for NAREF – Step 3: Daily Multiyear Solution – combination of all normal equations for orbits, EOPs, and all IGS and CORS site positions

Multiyear CORS (cont. ) – Step 4: Weekly Multiyear Solution – Stack 7 daily multiyear solutions and archive results – Step 5: Full Multiyear solution – Stack all weeks together to solve for site velocities • Schedule – Begin processing January 2006, complete in 3 -6 months