Future IGS & inter-technique SINEX combinations: Issues and challenges

D. Lavallée (aka Peter Clarke), R. Ferland, D. Thaller, T. Herring, R. Biancale.

1 Delft University of Technology, Newcastle University2 Natural Resources, Canada3 Astronomical Institute University of Berne4 Massachusetts Institute of Technology5 Centre National d’Etudes Spatiale

Intro

Discuss SINEX Products at:

Internal interface between internal (AC) products Affects IGS weekly and cumulative combination

External interface with external products Affects other technique services and ultimately IERS

How should the IGS guide the products at these interfaces?

Intro

Internal interface between internal (AC) products IGS guidelines Constraint and de-constraint

SINEX format Discontinuities External interface with external products

IERS Unification Workshop Potential new IERS products Daily versus weekly New products, troposphere and local ties

Preliminary Recommendations

The Internal Interface: Constraint & De-constraint

Numerical Issues Singular Matrices Near Singular Matrices (unpredictable

effects) Unremovable/Unavailable Constraints

Normal equations versus solutions Automation = Unattended

Needs also automated Quality Control Software/procedure Changes:

Ideally, provide parallel solutions Minimally, provide Warning

SINEX 1.0, 2.0, 2.01, 2.02 (Proposal 2.10) -> SINEX 2.x

Extensive format – Blessing and curse Evolving requirements

Multi service Always growing-No going back! Backward Compatibility

SINEX in Use Someone gives a subset (AC) Someone takes a subset (Combination Center/User) Format compliance of a file is never fully checked or

required, and historically is never perfect. SINEX file + format description is not enough!

Requires Agreement on subset of format used The unwritten rules The informally accepted bits IGS guidelines would help here

Multi-technique SINEX software?

SINEX 2.x

Historical/Typical format development cycle

Someone Needs New parameters

They think of away to do it

Proposalmade and

tested

ImplementationAnd use

Official Format Description

(Full documentation)Implementation

and use(informal or

no documentation)

Common or extensive usage by some/all

e.g. discontinuities format (IERS, IGS in use), current proposals (GGOS-D in use)

SINEX:Issues and Challenges

Unwritten rules, missing documentation, informally accepted bits, fully in use but not “official” parameters

Can sometimes make life difficult (particularly combination centers and other users)

Interrupts automation Discourages product use by new groups Allows misinterpretation of SINEX products. Corrupts historical archive

Will we ever move to a format first, implementation second approach?

Would need multi-service working group or panel Would need regular deadlines for proposal consideration,

proposal acceptance and proposal documentation Could consider data center side checking of sinex files

Discontinuities: Error in Rate Due to Known Offsets

Discontinuities

Lots of people have this problem Possibilities for common effort Offset database

Logical extension of site logs database

IGS Discontinuities SINEX Submission (SINEX+Wiki) Agreement/locking of records Offset prediction (e.g. earthquakes)

IERS Unification Workshop Action items 1/2

This is a IGS specific summary! Full details: IERS website -> Organisation -> Workshops

SINEX Extension of Parameterization / Naming

Generation of daily (24-hour) SINEX files (rapid solutions). Coordinates, velocities, EOP’s, troposphere, ionosphere.

Start the reporting of the troposphere parameters in the daily SINEX files

A priori representation of the ERPs: ACs should converge to a unique representation (interpolation) of the a priori ERP values as a linear function (linear interpolation) between the vertices.

Modeling standards for next ITRF : Technique-specific forms (a template) are provided by IVS, IGS, ILRS, IDS.

Generation of a unified form, forms filled and returned by all ACs Atmospheric loading should be reconsidered after tests by van Dam et al.

Recommend 3 receivers at fundamental sites, at least 2, One master station (of the three) should be analyzed by the IGS. The 2 (or 3) antennas may never be changed at the same time. It is not yet clear who will process the local “network”

IERS Unification Workshop Action items 2/2

Optimum solution sinex versus sinex for combination

Investigations Investigate the reason for cut-off angle dependent effects and

elevation-dependent weighting. ACs should freeze their selection of processing options and models between two reprocessing activities

Further studies are required to understand the bias between SLR and microwave GPS orbits

IDS and IGS to investigate improved radiation pressure models and parameterizations to reduce impact on the geocenter estimates, especially the new satellite box- and wing-models from UCL

Study the influence of the arc length and orbit constraints on geocenter estimates

IGS should consider applying the ionospheric corrections of higher order to be more consistent with the other Services’ products

Daily vs weekly products

General issues of consistency Some applications call for daily coordinates. Advantages to linking certain parameters across a

number of day boundaries, or entire week. E.g. Solar radiation parameters and Center of

mass estimate.

The External Interface: Troposphere Combination for GPS and VLBI

Correlation with station coordinates Stabilization (especially if local tie is missing)

Improvement in height repeatability (negative values) for most sites if Trop Zenith delays are combined.

Improvement is independent of agreement/disagreement with theory

The External Interface: Local tie (LT) validation

Including troposphere parameters into the combination provides an independent evaluation of LT

The External Interface: Local tie (LT) validation

Using UT for GPS-VLBI local ties

Recommendations: Internal products

COMBI-1: Define and maintain IGS conventions/procedure/guidelines document

COMBI-2: Use agreed set of models (currently IERS 2003) Essential for both internal (GNSS) and external (other services, IERS) product interface.

Recommend that SINEX files detail applied models and procedure. A SINEX block could be defined specifically to include this information.

COMBI-3: Report all apriori constraints, ensure they are removable. Unconstrained solutions are preferred. Loose (2-3 order of magnitude than the estimates

uncertainty) may be used. Inner (origin, orientation, scale) constraints acceptable.

COMBI-4: Minimize equipment changes due to GNSS modernisation The modernization should be coordinated to minimize equipment changes. Multiple

receivers and antennas should be used in parallel at core sites, there should be a clear procedure for handling the processing in these cases.

COMBI-5: Mechanism to contribute and share station discontinuity information

All users of station coordinates time series can potentially contribute to and benefit from this.

Recommendations: External products

COMBI-6: AC’s and hence IGS combination includes as many of the co-location sites as possible.

COMBI-7: Include troposphere parameters in the SINEX files. Natural extension to the existing coordinates parameters, to which they are

correlated. They can be combined with estimated troposphere from other techniques such as VLBI and DORIS to good effect. This should be done in conjunction with an upgrade to SINEX Version 2.x

COMBI-8: Provide rapid combined IGS SINEX Product. Include a selected set of stations (important: Wettzell, Kokee Park, Tsukuba)

and pole positions to help to improve VLBI UT rapid solution.

COMBI-10: That the mechanism to extend the SINEX format ensures backward compatibility, full documentation and encourages use of the official format

COMBI-9: Provide mechanism to stream extended products for inter-technique combinations via IGS

Where IGS AC’s can provide extended products (e.g. daily sinex, or normal equations of extended parameterisations) for inter-technique combinations, AND these products are directly related to the IGS products, that these products are streamed via IGS.