IGS LEO JASON-1 orbit campaign 2003

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		*CHAMP campaign* *JASON-1 campaign*
	*Orbit comparisons*	*Tracking data analysis*	*Precision estimates*

The JASON Orbit Comparison Campaign is the second campaign run in the framework of the IGS LEO Pilot Project. Based on experience from the earlier CHAMP orbit campaign some changes have been introduced in the campaign set-up:

Some additional analysis will be included, notably the processing of tracking data other than SLR, and a reference frame collocation analysis.
The selected campaign period (29 days) is longer than that for CHAMP (11 days). This makes the statistical results more representative for the absolute orbit precision. At the same time it makes it possible to exclude certain sections of the orbit solutions that coincide with spacecraft attitude events or orbit manoeuvres.
The orbit velocity will also be analysed.
Results will be presented in directions radial, along-track, cross-track and norm. For CHAMP, orbit precision analysis only considered the norm of the error vectors.
If mutliple solutions are available from a single centre, the latest solution will not simply replace the previous contribution (which was the case with CHAMP), but all solutions will remain. However, some analysis will only include the most precise solutions. This will hopefully avoid the confusion that has occassionally appeared in discussions relatred to the CHAMP campaign results.
More information is provided on the nature of the POD solution, to assist in the correct interpretation of the analysis reuslts.

As with CHAMP, the campaign will continue for as long as new contributions are submitted. Updates of the webpages may not always be immediate after submission of a new solution, but a considerable effort is put into keeping these pages up to date. The table below summarizes the solutions that are currently included in the JASON-1 campaign:

*Centre*	ID	*Solution description*
asi	ext	Reduced dynamic solution, external attitude data, GPS
	int	Reduced dynamic solution, internal attitude model, GPS
cnes	poe	Standard POE for geodetic data record, DORIS+SLR
	gps	Reduced dynamics solution, GPS
csr_	_ds	CSR dynamic solution, DORIS+SLR
	gds	CSR dynamic solution, DORIS+SLR+GPS
deos	grm	DEOS dynamic solution from CalVal campaign using GRIM5-c, DORIS+SLR
	jgm	DEOS dynamic solution from CalVal campaign, using JGM3, DORIS+SLR
esoc	ds2	ESOC reduced dynamic solution, DORIS + SLR
grgs	_gs	Dynamic solution, undifferenced GPS + SLR
gsfc	dyn	GSFC dynamic solution, DORIS+SLR
	red	GSFC reduced dynamics solution, DORIS+SLR
	rex	GSFC reduced dynamics solution, DORIS+SLR+Crossovers
	gps	GSFC reduced dynamics solution, GPS
	gs4	GSFC reduced dynamics solution, GPS + SLR
jpl	gps	JPL reduced dynamics solution, GPS
	poe	Early JPL CalVal orbits
ncl_	_ds	DORIS / SLR dynamic solution

Table 1: Solution identifiers used in the comparison results.
NOTE: standard fact sheets per solution are under preparation,
and will provide more detailled information on the POD methods.

The campaign period runs from day 154 of 2002 (June 3, 2002, MJD 52428, GPS week 1169 day 1) to day 182 of 2002 (July 1, 2002, MJD 52456, GPS week 1173 day 1), both inclusive. This corresponds to the cycles 15, 16 and 17 of JASON-1, with the exclusion of the very last day of cycle 17 which has minor data problems. For day 172 (June 21, 2002, MJD 52446) no attitude quaternions were available, and solutions that use quaternions show reduced precision for that day. Nonetheless, this day has not (yet) been excluded, due to other practical problems that arise from such exclusion.

Participating centers are requested to provide orbit solutions for this period, using satellite identifier L08 for JASON-1. Although SP3 format is preferred, contributions in SP1 format or POE formats can also be processed. Solutions either cover an entire JASON cycle with an overlap of about two orbital revolutions at either end (~ 4 hours), or should be provided in daily files with 2 hour overlap at either end (= 28 hour files starting at 22:00). Deviations from these requirements will probably not lead to significant errors, but an attempt is made to limit file conversions and interpolations as much as possible. Velocity values should be included in the SP3 files, but if these are missing they will be added by an numerical interpolation tool at ESOC. The preferred vector interval is 60 seconds or any smaller step that is in phase with 60 second intervals (i.e. 30, 20, 15, 10 seconds).

For any further questions or comments, please contact Henno.Boomkamp@esa.int .

Campaign analysis

The foreseen analysis for the JASON orbit campaign comprises the following;

Tracking residuals will be computed for SLR, DORIS, GPS (double differenced) and if possible altimetry crossovers.
Pairwise orbit comparisons between all solutions
Overlap comparisons, both between consecutive files of a single solution and between consecutive files of different solution, as far as possible
7-parameter transforms are estimated between each pair. this was already done for CHAMP as well, but for JASON an additional reference frame collocation analysis will be applied.
A mean frame will be estimated for SLR, DORIS and GPS. Solutions will be collocated with these mean frames, after which the associated tracking residuals will be recomputed.

Precision estimates will be derived similar as for CHAMP.
Please follow the links to have a look at the various analysis results.