ILRS Analysis Working Group, Orbit Benchmark

Study NERC Space Geodesy FacilityGraham Appleby

Presentation to AWG, 2002 Oct 3-4, HTSI, MD, USA

Orbit Comparisons

• Took analysis groups’ SolA, B and C geocentric ephemerides X and Xdot

• Formed differences, mainly from nerc, between values of X at each 2-minute epoch

• Resolved differences into along, across and radial directions.

• Plotted as functions of time

Orbit benchmark-comments (1)

• the initial orbits (solA) run off amongst themselves by between zero, 1m and 4m along-track;

• For ausg-jcet, the differences are essentially zero. For the second stage (solB):• some groups (csr, crl, nerc, iaa) appear to solve for all

orbital params;• others (jcet, asi, ausg) probably only solve for corrections

to the initial state vector and initial 4-day along-track accelerations;

• GEODYN groups agree with each other very well;• clear discontinuities at regular (4-day) intervals in the iaa

orbits.

Orbit benchmark-comments (2)

For solC orbits:

• GEODYN groups probably not correcting their orbits as a result of the solutions for stations and EOPs;

• Some good agreements (nerc - csr, crl, iaa; ausg – jcet; nsd – jcet);

• Some cm-level diurnal periodicities present in some differences.

Comparison of EOPs in SolC.snx

For those institutes that submitted SolC.snx files:

• Simple differencing of Xp, Yp and UTsat from a-priori C04 series given in sinex files

• Plots of results show:– asi, jcet apply loose constraints– dgfi apply strong constraints